UNIVERSITY OF KANSAS EL MISCELLANEOUS MUSEUM OF NATURAL HISTORY MAR 1 cere se HERP a 69 F553 98] Sexual Size Differences in Reptiles By Henry S. Fitch UNIVERSITY OF KANSAS LAWRENCE 1981 UNIVERSITY OF KANSAS PUBLICATIONS MUSEUM OF NATURAL HISTORY The University of Kansas Publications, Museum of Natural History, beginning with volume 1 in 1946, was discontinued with volume 20 in 1971. Shorter research papers formerly published in the above series are now published as Occasional Papers, Museum of Natural History. The Miscellaneous Publications, Museum of Natural History, began with number 1 in 1946. Longer research papers are pub- lished in that series. Monographs of the Museum of Natural History were initiated in 1970. All manuscripts are subjected to critical review by intra- and extramural specialists; final acceptance is at the discretion of the Director. Institutional libraries interested in exchanging publications may obtain the Occa- sional Papers and Miscellaneous Publications by addressing the Exchange Librarian, University of Kansas Library, Lawrence, Kansas 66045. Individuals may purchase separate numbers of all series. Prices for all publications of the Museum may be obtained from the Publications Secretary, Museum of Natural History, University of Kansas, Lawrence, Kansas 66045. THE UNIVERSITY OF KANSAS MusEuM OF NATURAL History MISCELLANEOUS PUBLICATION No. 70 February 27, 1981— Sexual Size Differences in Reptiles By Henry S. Fircu Museum of Natural History and Department of Systematics and Ecology University of Kansas Lawrence, Kansas 66045 UNIVERSITY OF KANSAS LAWRENCE 1981 UNIVERSITY OF KANsAs PuBLICATIONS, MusEuM oF NaTurRAL History Editor: E. O. Wiley Managing Editor: Joseph T. Collins Miscellaneous Publication No. 70 pp. 1-72; 9 figures Published February 27, 1981 MuseuM oF NaTuRAL History UNIVERSITY OF KANSAS LAWRENCE, KANsAs 66045 U.S.A. Printed by University of Kansas Printing Service Lawrence, Kansas CONTENTS MUN TER COPY GTB LIN es Pac es a | TG VDT) GUN 2 a ee ee 2 IVIPMIBETOIDS CAIN NEA EVLAUGS: 25.2 oo oe a 2 FEROS SO Nie bcs Se 0 Dee ae ee Ee eee ee 5 Onto mene tie (Cia eck Se et 6 rea CLON den ee 7 NmmOtated OVSteMiatiC MLASE go se i ial SIRS UCI S038 ne Oe te oe ee ee bf eG UEETOG 01 22 Ea 2 ee RO et Pe 13 DUA SCLP CLC ts ae ok ek ee 21 (O16 16:01 € hi) 72 Pe eee eles ee eae ee ee EE RE eR 31 OES CRS SON a a 32 IPSN ODES MR rex eNe UC) usher DBE TO) ee ies deta SNR a oe 42 APEENDLX 2. ROR ae see uta avo ese roe ne ere ere 53 JaNi PAE} Chin) 2119, Ge 0 [ae el ee ee On Ea WSR peer nar ere eel ee eee ea 67 INTRODUCTION The kinds of vertebrates that have males and females of just the same aver- age size are a minority. More often one sex or the other is larger. There are varying degrees of size difference, with a relatively large number of kinds hav- ing only slight sexual differences and relatively few kinds having major differ- ences between the sexes. The present study was undertaken to clarify these relationships in reptiles. Sexual size differences are better known in other groups of vertebrates than in reptiles. In fishes and amphib- ians females are usually larger than males, but there are noteworthy excep- tions. In both birds and mammals males are usually larger than females. In birds the most outstanding exceptions are the raptors, both Falconiformes and Strigi- formes, in which females are larger in varying degrees (Hill, 1944; Amadon, 1959). However, those raptorial birds that are mainly carrion-eaters or insecti- vores tend to have similar sized sexes, and the size difference is greatest in those kinds that take relatively large prey. In these predators the female takes larger kinds of prey, on the average and as a result the pair jointly occupying a territory, utilizes a wider range of prey which facilitates the securing of sufh- cient food, particularly during the critical period when nestlings are being fed. In accipitrine hawks Reynolds (1972) showed that the small male provides prey for the female during incubation and for the nestlings during the early stages of their growth, allowing the fe- male to spend her time at the nest, pro- tecting the brood against extremes of weather and predators; in the late stages of nestling growth, when the nestlings’ need for food is maximal, the female is active in hunting, and provides relatively large prey items. In mammals 84 species of 12 orders and about 30 families are known to have females larger than males (Ralls, 1976). Mammalian groups that consistently have females larger include vespertilio- nid bats, rabbits (leporids), three families of baleen whales, lobodontine seals, and cephalophine and neotragine antelopes. These diverse groups seem to have no common traits such as_ polyandry, strongly developed female aggression, development of female weapons, or fe- male dominance or matriarchy, that would account for the larger size of females. Presumably the mean adult size of each species and the size relationships of its sexes are the products of a com- plex of selective pressures that change through time. Optimum adjustment to available food, shelter, and other en- vironmental factors is involved. Some selective factors that might cause one sex or both sexes to deviate from modal adult size are: 1) need for the male to dominate potential mates and/or rivals; 2) need for the female to alter her re- productive strategy; 3) need for the spe- cies to reduce intraspecific (intersexual) competition for food and perhaps for other resources. Each species, in its unique ecological niche, has presumably been influenced by its own peculiar set of selective pressures. The present study is a preliminary attempt to show general trends of sexual size differences in living species of the class Reptilia, and to determine causes and correlations for them. Most previous studies (e.g., Klauber, 1943; Shine, 1978b) have not undertaken to show the amount of sexual size difference, but have merely stated that one sex or the other was the larger. No survey for the group as a whole has been made hereto- fore, but a number of authors have in- dicated sexual size differences in indi- vidual species. In the iguanid lizard genera Anolis and Sceloporus I deter- mined sexual size differences for a large number of species (Fitch, 1976, 1978) and indicated various ecological factors 2 MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY that affected them; Schoener (1970) and Schoener and Schoener (1971la, 1971b) likewise determined sexual size relation- ships in many species of Antillean Anolis. However, my present study is a prelimi- nary one because all figures obtained are in need of revision and/or refine- ment. Some data are based on inade- quately small samples. Literature rec- ords are sometimes based upon different kinds of data, hence widely disparate figures have been obtained for the same kind of animal in a few instances. As data have accumulated, it has become evident that the sexual size difference of a species is subject to variation in time and space, and perhaps cannot be rep- resented adequately by a single figure. ACKNOWLEDGMENTS The data that are the basis for this report were accumulated in the course of field work and museum studies over a 30-year period. W. Frank Blair (Uni- versity of Texas, Texas Natural History Collection), Charles M. Bogert (Ameri- can Museum of Natural History), W. E. Duellman (University of Kansas, Mu- seum of Natural History), and Robert C. Stebbins (University of California, Mu- seum of Vertebrate Zoology) kindly per- mitted examination of specimens in the collections under their care. Many per- sons assisted me in capturing the animals measured alive in the field, and in other ways; special thanks are due to Anthony A. Echelle, Alice Fitch Echelle, Chester W. Fitch, David C. Fitch, Virginia R. Fitch, Robert R. Fleet and Robert W. Henderson. My wife, Virginia R. Fitch, also helped me in various stages of gath- ering and analyzing the data and prepar- ing the manuscript. Richard Shine shared with me the early planning of the study. Richard A. Seigel kindly contributed unpublished data concerning sizes in Malaclemys, Lawrence E. Hunt likewise contributed measurements for two kinds of Anniella. The following authors gen- erously made available material from their unpublished manuscripts: Hugo Hidalgo, Tsutomu Hikida, John B. Iver- son, D. R. Jackson and R. Franz, Michael V. Plummer and D. B. Farrar. Alan E. Leviton kindly advised me concerning the correct names of various Asiatic species. W. E. Duellman kindly made available his measurements of Ecua- dorian snakes and lizards, including sub- stantial series of many species from Santa Cecilia and other localities in the Amazon Basin. These are indi- cated in Appendix I by the abbrevia- tion “WED ms.” METHODS AND MATERIALS Data pertaining to sexual size differ- ences were collected during the course of field studies of several dozen local populations, in Kansas, Mexico and Costa Rica, and by examining museum specimens in the University of Kansas Museum of Natural History, the Univer- sity of California Museum of Vertebrate Zoology, the American Museum of Nat- ural History and the University of Texas Natural History Museum. Also, figures for many species were obtained from published literature. Most publications contained pertinent information on only one or a few species but some had rela- tively large amounts of information. Much information about African snakes was obtained from Laurent (1956, mostly maxima), FitzSimons (1962, maxima only), and Pitman (1974, maxima only). Likewise M. Smith (1943) presented much information about Indian snakes (maxima only) as did Wright and Wright (1957) for North American species (max- ima and minima). Useful papers on en- tire herpetofaunas were those of Fuhn and Vancea (1961) for Romania (means), Dixon and Soini (1975 and 1977) for Amazonian Pert (maxima and minima), Duellman (1978) for Amazonian Ecuador and Hoogmoed (1973) for Surinam (means for some). Two exceptionally useful papers were those of Kopstein (1941) on Malayan snakes and Schwaner (1980) on Samoan skinks and geckos, both providing large series of individual SEXUAL SIZE DIFFERENCES IN REPTILES 3 measurements for many species. Ernst and Barbour (1972) provided the source of much information on turtles. Infor- mation on specific groups of reptiles was obtained from the works of Blanchard (1921) on king snakes (with individual measurements), Dixon and Huey (1970) on South American geckos of the genus Phyllodactylus (means), and Klauber (1937) on rattlesnakes (means) and espe- cially Schoener (1970) and Schoener and Schoener (197la and 1971b) on West Indian anoles (means). Male and female size was compared in the species studied by averaging all the adult measurements available for each sex. For snakes, lizards and croco- dilians the measurements used were those of snout-to-vent (S-V) in nearly all instances, but a few figures from the literature were based on total lengths in- cluding tail. Tails are relatively longer in male reptiles than in females, so in- clusion of the tail measurement would increase the apparent sexual size differ- ence in kinds having relatively large males but would reduce or nullify it in kinds having relatively large females. Many authors indicated total lengths for individual specimens, and the ratio of tail length to total length. In such in- stances I calculated snout-vent length for each specimen by subtracting tail length, assuming its tail ratio was the same as the mean for the series, but doubtless with loss of precision. Some authors showed the lengths S-V of in- dividuals or classes in histograms with- out presenting actual figures; I undertook to convert data from these graphs to the original figures. In turtles the length measurements used were those of the carapace for most species and those of the plastron for some others. Females of different reptile species investigated ranged from about % to 2% times mean male length. Since bulk increases as the cube of linear dimen- sions, it is implied that females weighed from about one-fourth to about 15 times as much as their male counterparts. Differences between the sexes in specific gravity and in bodily proportions, which might affect the accuracy of relative weight calculations based on_ linear measurements, are probably of minor significance in most instances. Rela- tively few authors have recorded actual weights for reptiles, but such data are highly desirable. Determining the lower limits of adult size was critical. In females, pregnancy or production of yolked follicles was considered adequate proof of sexual ma- turity. Likewise in males production of sperm was a valid criterion. However, in practice it was often not possible to check live animals or museum specimens for eggs or sperm. Instead, the develop- ment of various secondary sexual char- acters were relied upon. Also, the maxi- mum size for each sex and the size dis- tribution of a series were taken into account in deciding upon the minimum size to be included as adults. Inasmuch as small (younger) adults were usually much more numerous than large (older) adults whose cohorts had been reduced by normal mortality factors, the curve for each series tended to be skewed, with mean nearer the lower end. Even a small change in the minimum size in- cluded might have had important effect on the mean. The following abbreviations have been used: SSD = sexual size difference FMR = female-to-male ratio The latter was the linear measurement of snout-vent length, or shell length al- ways expressed as a per cent; for ex- ample male S-V = 350 mm, female S-V = 400 mm, FMR = 400/350 = 114; or, as a second example, male S-V = 400 mm, female S-V = 360 mm, FMR = 360/ 400 = 90. The figure for FMR has in all instances been rounded to the nearest whole number. Under Results such figures, based on averages for series of adult males and females, are presented for many species. 4 MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY These figures, obtained from a variety of sources, mostly from published litera- ture, represent four degrees of reliability. The most reliable are those figures based on the means of large statistical series (sometimes several hundred). Such rec- ords are distinguished in the lists by having both the name of the species and the figure representing its FMR set in bold face. Less reliable are figures based on means from fewer than ten measure- ments for either sex. These are distin- guished by the symbol x following the FMR figure. Thirdly, there are figures based on the FMR for the modes, when the author had indicated only the maxi- mum and minimum measurements for adults of each sex. For example: male S-V = 250 to 350 mm (mode 300), fe- male = 300-400 (mode 350), FMR = 350/ 300 = 117. Such records are designated by the letter “m” following the FMR figure. Even less reliable are ratios ob- tained from maximum measurements for each sex. Such figures are included only where it is believed that the author measured a substantial series of each sex, but often the number of specimens was not mentioned. Eliminating all such instances would have assured more con- sistent trends, but also would have elimi- nated many important groups for which no information was available otherwise. In order to avoid a spurious impression of accuracy, the actual FMR figures ob- tained from maximum measurements have not been presented, but instead a code has been substituted, as follows: FMR > 1385: ++++ FMR 126-135: +++ FMR 116-125: ++ FMR 106-115: + FMR 96-105: X FMR_ 86-95: — FMR 76-85: —— FMR 66-75: ——— PONE 007 9 The 548 taxa for which only maximum measurements for each sex are available are listed in Appendix II. In general these figures are considered to be useful at least for showing which sex is the larger, and whether SSD is large or small. They show significant trends in groups for which, otherwise, little infor- mation is available. For instance in the Asiatic Trimeresurus, 13 species were shown to have females larger, three spe- cies had the sexes about equal and only one was shown to have the male larger, in records mostly obtained from Smith (1943). Most samples that were used consist of statistical series of each sex reported in the literature, and usually the series represent a single locality or area. In a few instances it was necessary to com- bine measurements published by two or more authors; for several species of African snakes, means were obtained by combining figures of several authors in- cluding Broadley and Cock (1975), Fitz- Simons (1962), Laurent (1956), Loveridge (1953), Pienaar (1966), Pitman (1974), Schmidt (1923) and de Witte (1953), in various combinations. Each of these au- thors published the maximum figures for the series available to him, and the means for these maxima are, of course, relatively high, compared with means from randomly selected series that are available for most other species. Like- wise for several Asiatic snakes, averages were obtained from maximum measure- ments published by Pope (1935), Smith (1943), Malnate (1962), and others. In general, however, the figures in Appendix I are believed to be repre- sentative for each of the species in show- ing the approximate mean sizes of adults of both sexes and the usual range. Ap- pendix I will no doubt have some use- fulness in showing typical sizes for vari- ous species, since definitive statements about size are remarkably scanty in the literature. Even revisionary studies which treat lepidosis and body propor- tions in great detail usually contain no useful information concerning size. Often the only statement about size is that of the total length of the largest specimen SEXUAL SIZE DIFFERENCES IN REPTILES 5 examined (sometimes with no indication of its sex). Herpetologists have been prevented from fully utilizing size in systematic studies by the dogmatic con- viction that in reptiles growth is “in- determinate.” Actually the genetic size differences between species and subspe- cies could, in my opinion, provide some of the most useful taxonomic characters. In general, adult size in a reptile species is more variable than it is in a bird or mammal, but less so than in a fish. Adult size tends to be relatively homogeneous in turtles and lizards, less so in snakes; but within each of these groups there is much difference between families, gen- era and species in homogeneity of adult size. In the annotated systematic listing, under Results, binomials are used (re- gardless of subspecies) when only one population of a species was sampled, or for the nominate subspecies if other pop- ulations of the species are listed sepa- rately. The maximum sizes listed in the ap- pendices include few “world records” if any. They merely represent the largest male and female in the particular series utilized, and almost inevitably larger specimens will be found if they are not already known. Although most FMR figures were ob- tained from random samples of adults, there were several important exceptions. The figures for many West Indian anoles, from Schoener (1970) and Schoener and Schoener (1971a and 1971b) were based on the one-third of the adults of each sex that were the largest in each sample. The figures for Conant’s (1969) Mexican Nerodia were based on the 10 largest males and females of each sample. In a few instances, disregarding trinomials and minor geographic variants, I aver- aged the maxima for several geograph- ical populations to obtain a series (e.g., Schwartz, 1970). In a few instances as for the several African snakes the maxi- mum measurements for each sex pub- lished by various authors were combined to average for FMR. A series of specimens showing a sex- ual size difference usually has more dif- ference between the maxima than be- tween the means, that is, the difference between the male and female means tends to be magnified in the maxima. The trend of relationship between means and maxima are shown in Table 1. Even if the means are just the same, one sex or the other may grow to a larger max- imum size. RESULTS The large amount of data obtained bearing on sexual size differences in rep- tiles has revealed some significant trends within and between various taxonomic groups. Also it has raised many prob- lems that are not readily answered. For most reptile species knowledge of life history and ecology is still insufficient to interpret SSDs in terms of reproductive strategies, r and K selection or other ap- propriate concepts. Ontogenetic changes in sexual size differences are revealed for several spe- cies. For several others, geographic vari- ation in SSD is shown. In some cases SSD can be strongly correlated with be- havioral or reproductive traits or with climatic preferences. Table 1 shows FMR figures for 30 species of turtles, lizards and snakes for which large series of adults were avail- able. It compares various other param- eters with the FMR means, showing that in most instances the mode, median, and means for the 10 largest of each sex (or 5 largest, or 3 largest) approximate the series mean, but the ratio of maxi- mum male and female measurements is more variable. Except where otherwise indicated, by asterisk, the species in Table 1 are those measured by me in field studies of live animals or in studies of museum specimens. Excluding those 548 taxa for which only maximum measurements for each sex were available, 770 kinds of reptiles 6 MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY were checked for size difference between the sexes. Twenty-five had males and fe- males of approximately the same size, 371 had females averaging larger than males, and 374 had males averaging larger than females. For the whole group average female size was 104% of male size (66%-248%). ONTOGENETIC CHANGE Sexual size differences are discussed throughout most of this paper as if they were constant and species-specific. On- togenetic changes have been shown for a few kinds, but figures are less refined than could be desired. Although some studies were based on large-scale mark- ing of individuals, the survivors in the older age groups were generally so few that their means were subject to fairly wide margins of error. The usual trend seems to be growth at comparable rates in juveniles of both sexes, with divergence in size at adoles- cence, and little change in SSD during the period of slowing growth after aver- age adult size is attained. Table 2 shows male and female sizes (S-V) in successive TABLE 1. FMR (= ratio of female length to male length expressed as per cent). maxi- 10 5 3 Species N N x(FMR) mode median mum largest largest largest Turtles 3} 2 Gopherus agassizii* 59 32 92 89 79 95 90 92 92 Pseudemys scripta® 98 48 140 146 125 103 109 107 106 Terrapene ornata 78 163 101 100 102 103 103 103 104 Lizards Ameiva undulata 44 69 85 84 85 92 88 91 92 Cnemidophorus deppei 152 260 93 87 88 88 88 88 88 Cnemidophorus sexlineatus 88 96 101 101 100 102 102 103 102 Cnemidophorus tigris 46 ie 93 95 96 89 93 90 89 Eumeces fasciatus 120 180 99 100 100 96 98 98 98 Eumeces obsoletus 146 128 102 102 104 106 104 104 105 Ophisaurus attenuatus 733 420 95 95 96 92 92 92 91 Sphenomorphus cherriei 39 61 100 102 101 109 103 106 109 Snakes Agkistrodon contortrix 116 98 93 94 95 76 85 80 cif Bothrops atrox 59 53 115 111 116 116 122, 122 119 Carphophis vermis 90 re) 117 116 114 113 119 116 114 Coluber constrictor 181 177 110 109 107 109 ies iT 116 Diadophis punctatus 906 408 BE 114 1 Wy 126 119 123 123 Dipsas catesbyi 99 105 96 101 101 109 126 105 108 Elaphe obsoleta 253 168 98 94 103 87 88 89 89 Lampropeltis calligaster 78 75 91 93 91 90 88 89 90 Lampropeltis triangulum 47 35 97 99 97 85 93 92 91 Leptodeira annulata 45 51 108 103 107 110 108 108 109 Liophis miliaris* 123 244 124 123 130 134 141 139 139 Micrurus fulvius* 46 92 119 122 116 158 142 144 158 Nerodia sipedon 55 46 132 134 134 137 138 137 134 Pituophis melanoleucus 59 55 101 104 104 91 100 99 96 Sonora episcopa* 347 302 100 100 100 100 100 100 100 Thamnophis ordinoides PAL 28 123 124 124 130 128 128 128 Thamnophis sirtalis 215 282 123 PAR 160 182 VAT 180 180 Tropidoclonion lineatum* 137 175 117 15 132 131 130 124 129 Virginia striatula* 90 55 116 119 123 119 123 127 117 * Clark, 1964, for Virginia striatula; Force, 1936, for Tropidoclonion lineatum; Gans, 1964, for Liophis miliaris; Kassing, 1961, for Sonora episcopa; Moll and Legler, 1971, for Pseudemys scripta; Quinn, 1979, for Micrurus fulvius; Woodbury and Hardy, 1948, for Gopherus agassizii. SEXUAL SIZE DIFFERENCES IN REPTILES i annual age classes of seven reptile spe- cies including one lizard and six kinds of snakes. In the account of Alligator mississip- piensis based on a large scale field study by Chabreck and Joanen (1979), it is shown that juvenile males grow faster than females, and although there is some slowing of growth at adolescence, adult males continue to grow faster than adult females. Hence, in the oldest alligators SSD is extreme. Ernst (1977) presented figures on the sizes of adult Clemmys muhlenbergii of different ages that seemed to indicate little change in the size ratio of the sexes as the turtles grew older. In series that were 6, 7, 8, 9, 10 and 11 years of age the female-to-male size ratios were, respectively, 93, 92, 93, 93, 94 and 93 per cent. Both sexes increased in size by 31% from the 6- to 1l-year-old class. There were 10 to 17 turtles of each sex in each year class, except 1l-year-olds with 4 males and 7 females. In the large Neotropical iguanid, Basiliscus basiliscus, both sexes grow at approximately the same rate for nearly a year, to about 2.5 times hatchling size of 42 mm (S-V). Thereafter, approach- ing adolescence, the females grow more slowly than males. In the oldest basilisks (6+ years) female to male ratio has de- creased to about 72% (8 229mm, ¢? 165) but SSD is less in some localities (Van Devender, 1978). GEOGRAPHIC VARIATION Polytypic species have shown geo- graphic change in the size ratio of the sexes in every case tested, and it may be speculated that such change is the rule. Several examples are presented in Tables 3 to 5. Uta stansburiana, being abundant and widespread, provides one of the best examples, and the data for 19 local populations are compared in Table 3. The first 10 populations are from the western United States and Mex- ico from 45° N in Oregon to 28°20’ N in west-central Sonora, and FMRs range from 87.5 to 100.1. There is not a clear- cut latitudinal gradient, but in all six of the more northern populations (north of latitude 35°) FMR exceeds 93 (x = 95.7) whereas in the four more southern pop- ulations FMR is consistently less than 93 (x = 90.0). Nussbaum and Diller (1976), who studied the northernmost popula- tion in north-central Oregon, found that male aggression was little developed, compared with that of more southern populations. The nine populations rep- resented in the lower half of Table 3 are from various islands in the Gulf of California. Their sexual size dimorphism is comparable to that of mainland popu- lations. Both in having males relatively large in insular populations and in hay- ing males relatively larger in southern than in northern populations, Uta stans- buriana follows trends that are wide- spread in lizards. Cnemidophorus tigris is another wide-ranging, polytypic lizard species and samples from the northern and southwestern parts of the range showed the sexes to be approximately equal in size with males averaging slightly larger. However, in samples from the southeast- ern part of the range, south-central New Mexico (Medica, 1967) and Reeves County, Texas (Fitch, 1970) males aver- aged markedly larger than females (FMRs 87 and 94). Table 5 shows sexual size differences in geographic populations of Chrysemys picta. This wide-ranging species is typi- cal of many freshwater turtles in having females much larger than males, the latter maturing at relatively small size and early age. In this table, for each population, the length (plastral) shown is the minimum at sexual maturity, rather than the adult average, as in most other instances. Although no well defined gra- dient is discernible, there seems to be a general trend toward having relatively much larger females in the southern half of the United States than in the northern half. Extreme size differences in the sexes results from early sexual MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY S96BT “YOU FPOGT “epeyny GO6T “epeyxny SLOT “YOU C96T “UA LET ‘TeYVWN O96T “Yd AYLOYINY AYUNYUL TENXIS ,. 86 ie —= 99% yyysry 066 Bib Sa 196 bL6 Sil St8 qyqwadaas SLL Sel YOL =. 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In more northern re- gions male maturity is delayed until somewhat larger size is attained, at four or five years, and female maturity re- quires six to ten years. Iverson (ms) studied SSD in the Mex- ican mud turtle, Kinosternum hirtipes. In a sample of 306 adult males and 237 adult females FMR was 92.3. However, the species has many discrete popula- tions isolated from each other in separate drainage basins and differing in various TABLE 3. Geographic Variation in Sexual Size Ratios in Uta stansburiana. FMR (Female to male length ratio Authority per cent) S-V 6 N S-V@ N Geographic origin 93.9 48.4 45.4 North Central Ore. 95.0 47.55 (47) 45.04 (25) Hart Mtn. Antelope Refuge, Ore., 42°25/ 100.1 48.56 (107) 48.72 (104) 3-4km W Grantville, Utah, 40°36’ 96.5 48.26 ( 27) 46.53 ( 36) 8 kmN Lovelock, Nev. 40°12’ 93.5 48.22 (18) 45.15 ( 26) Kyle Canyon, Nev. 36°15! 95.6 51.85 (55) 49.56 ( 69) 8 kmN Mojave, Calif. 35°06’ 91.5 51.71 (102) 47.38 (114) S Mtn, Phoenix, ATIZ OOS 20% 92.4 55.34 (101) 51.11 (91) 16km NW Casa Grande, Ariz. 32°57’ 88.6 50.39 (18) 47.44 ( 16) Dona Ana and Luna Cos, NM 31°50’ 87.5 53.29 (17) 47.05 (21) 7kmE Estero de Tastiota, Sonora 28°20’ 94.0 44.59 ( 32) 41.83 ( 24) Isla San Francisco 91.0 50.88 (16) 46.28 ( 25) Isla San José 88.6 45.95 (20) 40.67 (18) Isla Partida Sur 91.1 44.88 (17) 40.89 (18) Isla San Marcos 91.1 51.50 ( 34) 46.85 ( 34) Isla Carmen 93.1 49.56 (25) 46.04 ( 26) Isla Tortuga 91.5 48.50 (18) 44.39 ( 26) Isla Tiburon 92.2 52.48 (27) 48.36 (47) Isla Partida Norte 94.4 47.21 ( 39) 44.60 ( 30) Isla San Esteban Nussbaum and Diller, 1976 Parker & Pianka, 1975 Parker & Pianka, 1975 Parker & Pianka, 1975 Parker & Pianka, 1975 Parker & Pianka, 1975 Parker & Pianka, 1975 Parker & Pianka, 1975 Parker & Pianka, 1975 Parker & Pianka, 1975 Dunham & Tinkle, 1978 Dunham & Tinkle, 1978 Dunham & Tinkle, 1978 Dunham & Tinkle, 1978 Dunham & Tinkle, 1978 Dunham & Tinkle, 1978 Dunham & Tinkle, 1978 Dunham & Tinkle, 1978 Dunham & Tinkle, 1978 TABLE 4. Geographic Variation in Sexual Size Ratios in Cnemidophorus tigris. FMR 2 to ¢ ratio, percentage S-V ¢ S-VrangeN 9 S-V range N Region 99.8 94.8 (93-97 in 10) 94.6(91-102 in 10) SW Idaho 99.4 77.6 (97-66 in 22) 77.1(88- 69in 9) L. Colorado River 97.7 85.6 (79-95 in 52) 83.7(71- 98in 43) Test Site, S Nevada 93.6 83.5 (79-95 in 44) 78.1(71- 87in 79) Reeves Co., Texas 87.1 82.24(64-97) 71.6(54- 88) S-Central New Mex. Authority Burkholder & Walker, 1973 Fitch, 1970 Medica, 1967 Vitt & Ohmart, 1977b Tanner & Banta, 1966 10 MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY TABLE 5. Relative Lengths of Males and Females of Chrysemys picta at Sexual Maturity. Male at sexual maturity age FMR length (yrs.) length LS 70 120-125 175 60-65 2-3 100 162 65 2-3 105 158 80-85 34 130 153 80-90 130 147 85+ 125 -= 144 80 5 110-120 141 95-100 4-5 135-140 139 90 120-130 118 80-90 4 100 1 i 95-100 4-5 135-140 characters including SSD. Drainage basins in Mexico that yielded substantial series, and the FMRs obtained from them were as follows: Papigochic 85.9 (22 males, 23 females), Conchos 86.5 (56 males, 42 females), Nazas 92.0 (20 males, 13 females), Santa Maria 92.3 (39 males, 25 females), Aguanaval 95.8 (28 males, 22 females), Mezquital 100.2 (28 males, 29 females). Seven other populations represented by only small samples had FMRs exceeding 100. Iver- son found a trend for the smaller drain- ages and those containing lakes to have populations of relatively small turtles in which there was little size dimorphism or else female-favored size dimorphism. In the Neotropical lizard, Anolis cupreus, massive samples are available to show geographic variation in sexual size differences over the range. The males are markedly larger. In A. c. cupreus and A. c. spilomelas of the low- lands of northwestern Costa Rica, FMRs are 88 and 84, respectively, and 82 in macrophallus of Guatemala. But in A. c. hoffmanni at the upper altitudinal limit, on the Meseta Central of Costa Rica, FMR is 97. The intraspecific trend in A. cupreus conforms with interspecific trends in the large genus Anolis. Those kinds in severely seasonal climates where cold or drought prevent reproduc- tion over part of the year, with a rela- Female at sexual maturity age Region (yrs.) (state in USA) Authority Ss. DE Cagle, 1954 4 La., Ark Moll, 1973 4-5 Tenn Moll, 1973 4-6 Cent. Ill Moll, 1973 New Mex Christiansen and Moll, 1973 S. Minn Legler, 1954 7-10 S. Mich Gibbons, 1968 7-8 Wisc Christiansen and Moll, 1973 N. Mich Cagle, 1954 4-6 Penn. Ernst, 1971 7-8 S. Mich Wilbur, 1975 tively concentrated and stressful breed- ing season, have relatively larger males than do kinds living in climates that tend to be aseasonal, such as rain forests and montane cloud forests. Ameiva auberi is a small terrestrial teiid lizard that is widely distributed over the West Indies, with named sub- species on many islands. There is much intraspecific variation in size and also, apparently, in size ratios of the sexes, but figures are available only for maxi- mum sizes of each sex (Schwartz, 1970; McCoy, 1970). Excluding small samples (those in which less than 28 specimens were available) there were 15 population samples from Cuba and neighboring is- lands, and 7 samples from the Bahamas, with from 28 to 123 specimens. FMRs ranged from 95.7 (auberi, N coast of Cuba) to 59.6 (multilineata, Berry Is- lands, Bahamas). For the entire group of 22 populations, FMR averaged 79.3, but it averaged much lower (70.3) for the 7 Bahamian subspecies than for the 15 from Cuba and vicinity (82.6). De- spite this regional difference, the sub- species showed no obvious correlation with size of island, body size, or any other obvious factor in the trend of their sexual size difference. In West Indian anoles presence or absence of congeneric competitors seems to be a major factor affecting SSD. SEXUAL SIZE DIFFERENCES IN REPTILES it Schoener (1970) and Schoener and Schoener (1971a, 1971b) have published figures for many populations, in sym- patry and allopatry, showing varying de- grees of character displacement. For each species I arbitrarily selected one FMR figure when several were available, to include in Appendix I and the anno- tated list. SSD in anoles is further dis- cussed below in the annotated list. ANNOTATED SYSTEMATIC LIST In the following list the various groups of reptiles are treated in the usual systematic sequence. Under each major group, genera and species are listed alphabetically, with a figure or symbol indicating FMR of each species, followed by brief comments on the trends within the group, and possible explanations for them. The groups first tested were fam- ilies but some were combined into larger systematic units or divided. Data were obtained for relatively few kinds of tur- tles, hence there is only one list for the order Testudines, but there are many lists for the order Squamata and its main subdivisions, the snakes and lizards. In the large ophidian family, Colubridae, 24 subfamily units are separately listed, because substantial series of species were available in some, with distinctive trends setting them off from other sub- families. Similarly, the large family Iguanidae is divided into seven subfam- ily units to treat with the 226 taxa for which definite FMR figures are avail- able. I follow Etheridge (1964, 1965, 1966) in the iguanid subfamilies recog- nized, except that I have also included “crotaphytines” and “phrynosomines” not formally designated by Etheridge but implied by him in dissociating Crota- phytus and Phrynosoma from the scelo- porine genera. Both are sufficiently dis- tinctive in the trends of their SSD to merit separate treatment. Testudines Chelonia mydas 106 m, Chelydra ser- pentina 100 x, Chersina angulata ———, Chrysemys picta 139, Clemmys guttata 100, C. marmorata 100 m, C. muhlen- bergii 107, Deirochelys reticularia 194 m, Emydoidea blandingii 95, Emys orbicu- laris 106 m, Eretmochelys imbricata 104 m, Geochelone elephantopus ephippium 82, G. e. vicina 99, G. pardalis +++, G. p. babcocki +, G. radiata 93 x, Gopherus agassizii 92, G. polyphemus 106 m, Grap- temys barbouri 195 m, G. geographica 196, G. kohni 182 m, G. nigrinoda 143 m, G. oculifera 184 m, G. ouachitensis 167, G. pseudogeographica 169, G. pulchra 248 m, Homopus areolatus ++, H. bou- lengeri X, H. femoralis ++, Kinixys bel- liana +, K. b. nogueyi X, K. erosa ———, K. homeana X, Kinosternon bauri 101 x, K. b. palmarum 121 m, K. flavescens 98, K. subrubrum 118 m, K. s. hippocrepis 100, Lepidochelys olivacea +, Macro- chelys lacertina 86, Malaclemys terra- pin 158 m, M. t. centrata 144 x, M. t. tequesta 141, Malacothoerus tornieri ++, Psammobates oculifer +, P. tentorius ++++, P. t. verroxi ++, Pseudemys concinna 117 m, P. floridana 139, P. f. “suwanensis” 143 m, P. f. texana +, P. rubriventris 116 x, P. scripta 140, P. s. troosti 108 m, Rhinoclemys annulata +, R. areolata +, R. funerea —, R. nasuta +, R. pulcherrima +, R. p. incisa 117 x, R. p. manni ++, R. p. rogerbarbouri +++, R. punctularia +, R. p. diademata +++, R. rubida ——, R. r. perixantha +, Sternotherus carinatus 98, S. minor 105, S. odoratus 105, Terrapene carolina 91 x, T. coahuila 93, T. ornata 102, Testudo graeca 97 m, T. kleinmanni +, Trionyx muticus 158, Trionyx spiniferus emoryi 236 m, T. s. ferox 168, T. s. pallidus 182 m. The FMR samples, representing 50 taxa (all cryptodiran) averaged 129.8 + 5.68. Females were larger in 70%, males in 22% and sexes were equal-sized in 82%. The most striking aspect of these figures is the relatively large size of females in most species, and especially in those of highly aquatic habits. In those kinds having the males larger, the 12 MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY difference is usually small, and most such species have terrestrial tendencies. Al- though precise figures are not available for any pleurodiran, Roze (1964) wrote of the giant South American river turtle Podocnemis expansa that adult females averaged about two feet in shell diam- eter, males about 1%, hence FMR prob- ably approximates 133. Relative large female size is most extreme in the emydid genus Graptemys. In G. pulchra of Alabama adult male size is 80-120 mm, whereas adult females are 212-285 mm (Shealy, 1976). Males mature in their third or fourth year, but females require about 14 years to mature. In soft-shelled turtles the SSD is almost as great. Plum- mer (1977) found FMR of 158 in Trionyx muticus. Associated with this great size difference there was striking difference in habits and behavior. Males spent more time in basking and tended to keep in shallow water in relatively small home ranges, but in contrast the large females spent their time in deep water in the main channel of the river, with relatively long movements upstream and down- stream. Plummer and Farrar (ms) stud- ied food habits of T. muticus from the stomach contents of 105 adults of this same population. The diet of males was found to be more diverse than that of females, and significantly different nu- merically and volumetrically. Approxi- mately 71% of the food volume taken by females consisted of aquatic organisms, of which larvae of the trichopteran Hy- dropsyche were by far the most numer- ous, whereas approximately 67% of the food volume taken by males consisted of terrestrial items. The most important items for males, in order of decreasing volume, were: mulberries 34.3% (48), cottonwood seeds 15.3% (892), trichop- teran larvae 10.4% (456), dipterans 6.3% (139), beetles 4.2% (206), fish 1.7%, lepi- dopterans 1.2% (9). In contrast, the most important items for females were: tri- chopteran larvae 43.7% (2430), fish 20.1%, mulberries 16.3% (28), crayfish 4.9% (7), beetles 2.3% (17) and ephemeropteran larvae 1.9% (59). No significant relation- ship was evident between prey size and turtle size, nor between prey size and sex of turtle. Males are larger than females in the tortoises Geochelone species and Go- pherus agassizii, the box turtle Terra- pene carolina, the emydids Clemmys muhlenbergii and Emydoidea blandingii, the chelydrids, Chelydra serpentina and Macrochelys lacertina, and the kinoster- nid, Kinosternon flavescens. In all of these and in many other kinds of turtles male aggression is known to occur. Har- less (1978) summarized the literature on agonistic behavior in turtles. Eleven ac- counts pertained to Terrapene and 11 others to testudinids (Chersine, Geo- chelone, Gopherus); 8 were of chelydrids, 8 were of Clemmys, 5 were of kinoster- nids (Kinosternon, Sternotherus), 4 were of cheloniids (Chelonia, Eretmochelys), 2 were of Chrysemys, 2 were of Trionyx and 1 was of Graptemys. Male combat is prominent in some species in which the sexes are nearly the same size, or in which the female is a little larger. In Chelonia mydas Booth and Peters (1972) described attacks on the mating male by “attendant” males. In captive turtle groups, including tortoises, box turtles, and Clemmys in- sculpta, males are known to form domi- nance hierarchies. Agonistic behavior consists of biting and ramming. Threat- ening posture, rapid approach, hissing, and odors including those of the feces, reinforce dominance. Dominant males may inhibit the feeding and mating ac- tivities of other males. Under natural conditions turtles are not known to have polygynous mating systems, and males rarely, if ever, maintain discrete terri- tories. It should be noted that much differ- ent FMRs have been obtained for the same species of turtles in a few instances when two or more authors have pub- lished different sets of figures. For in- stance, for Chelydra serpentina an FMR of approximately 100 is indicated both SEXUAL SIZE DIFFERENCES IN REPTILES 13 from White and Murphy’s (1973) plastral measurements and Christiansen and Burken’s (1979) carapace measurements, whereas Mossiman and Bider’s (1960) carapace measurements of a Quebec pop- ulation indicate FMR of 88. For Kino- sternum subrubrum Mahmoud’s (1967) figures indicate FMR of 100 whereas Iverson’s (1979a) indicate FMR of 118. It needs to be determined how much such differences actually reflect geographic or ontogenetic variation vs. authors’ biases in collecting, or in their criteria for set- ting the lower limits of adults of each Sex. Squamata: Sauria GECKONIDAE. Aristelliger george- ensis ——, A. hechti ——, A. lar ——, A. praesignis ——, Coleodactylus amazoni- cus 105, Coleonyx brevis X, C. elegans X, C. mitratus X, C. variegatus 107, C. v. utahensis 114, Cosymbotus platurus 99, Cyrtodactylus malayanus 109, C. pubis- culus 110, Eublepharus angramainyu 89 x, Garthia dorbignyi X, G. penai X, Gecko japonicus ———, G. vittatus X, Gehyra australis 104 x, G. oceanica 97, G. variegata 99 x, Gonatodes albogularis 100, G. annularis 101 x, G. concinnatus 99 x, G. humeralis 106 m, Hemidactylus frenatus 96, H. mabouia 106 m, H. turci- cus 106, Heteronotia binoei 108, Lepido- dactylus lugubris 102 x, Lygodactylus angolensis X, L. capensis X, L. picturatus —, Pachydactylus punctatus +, P. tuber- culosus —, Palmatogecko rangei ++, Peropus mutilatus 99, Phelswma_lati- cauda ——, P. lineata ——, P. madagas- carensis —, Phyllodactylus angustidigi- tatis 95, P. europaeus 98 x, P. gerrhopygus 98, P. inaequalis 100, P. interandinus 105, P. johnwrighti 103, P. kofordi 102, P. lepidopygus 115, P. microphyllus 100, P. reissi 97, P. tuberculosus 102 m, P. ventralis 100, Pseudogonatodes guianen- sis 102 x, Ptenopus garrulus 101 x, Sphae- rodactylus argivus 99, S. argus 113, S. a. bartschi 106, S. cinereus X, S. copei astreptus X, S. c. pelates X, S. c. websteri X, S. lewisi 108, S. oxyrhinus 111, S. o. dacnicolor 102, S. rosaurae X, S. semasi- ops 110, Tarentola americana —, T. mau- ritanica 84, Thecadactylus rapicaudus 106 x. Among 43 species of geckos tested, FMR ranged from 84 to 115, and aver- aged 101.9. Males were larger in 13 species; females were larger in 26, and the sexes were equal in four. Eleven of these geckos were members of the large genus Phyllodactylus and in all but one of these males and females averaged nearly equal in size. The exception was P. lepidopygus having a FMR of 115. The remaining 32 species of geckos were in 15 genera representing Europe, Africa, Asia, Australia and South and Central America. The species having relatively largest males, Tarentola mauritanica (FMR 84) and Eublepharis angramainyu (FMR 89) are from the temperate-zone climate of Spain and Iran, whereas most of those with relatively large females were from equatorial regions. Geckos are known to maintain terri- tories, with visual cues and vocalizations playing important roles. Males are more aggressive, and in some instances there is dimorphism, with males more conspic- uously marked. Large males would seem to have a selective advantage in defend- ing territories and securing mates. Espe- cially where there is a relatively short and concentrated, and therefore stressful breeding season, large size might confer selective advantage. Oviparity is the rule (except in New Zealand) with a two- egg clutch (or one egg, in sphaerodacty- lines and a few small geckonines). The hatchlings are relatively large. Large hatchlings probably have better chances of survival than small ones. Doubtless there is selective pressure for females to produce larger young, counteracted by selection for light weight, in these small scansorial lizards dependent on their digital lamellae to cling to surfaces that are sometimes smooth and vertical. IGUANIDAE. This is a large and diverse family of lizards, mostly of the Western Hemisphere. They range from 14 MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY small to large. They are vision-oriented, and there are usually special display organs in the males, less developed or lacking in the females. The displays are stereotyped and species-typical, and serve both in territorial aggression and defense and in courtship. Most iguanids are oviparous but several genera of basiliscines, sceloporines, phrynosomines and tropidurines have some viviparous species. Average clutch size ranges from just one in anolines to several dozen in large mainland iguanines. ANOLINAE. Anolis aeneus 71, A. ahli ———, A. allisoni 74, A. allogus 75, A. alumina —, A. alutaceus 92, A. an- gusticeps 88, A. aquaticus 89 x, A. argil- laceus 81, A. attenuatus 95, A. auratus 104 x, A. a. sipaliwinensis 104, A. baleatus ——, A. b. litorisiloa ——, A. b. multi- struppus —, A. b. scelestus ——, A. ba- horucoensis southerlandi ——, A. bara- honae —, A. barkeri ——, A. bimaculatus 71, A. biporcatus 102, A. biscutiger 106, A. bombiceps 110 m, A. bourgaei 103, A. bremeri 70 x, A. brevirostris 89, A. capito 106, A. carolinensis 79, A. car- penteri 105 x, A. chlorocyaneus 76, A. christophei 92, A. chrysolepis 105, A. coelestinus 78, A. concolor 74, A. cooki 70, A. crassulus 88 xX, A. cris- tatellus 79, A. cupreus 88, A. c. hoff- manni 97, A. c. macrophallus 82, A. c. spilomelas 84, A. cuprinus 73, A. cuvieri 92, A. cybotes 77, A. damulus 110 x, A. distichus 87, A. d. biminiensis 90 x, A. dolichocephalus sarmenticola ——, A. d. portusalus ——, A. dollfusianus 94, A. equestris 93, A. evermanni 74, A. ex- tremus ——, A. frenatus 82, A. fuscoau- ratus 108, A. f. kugleri 102 x, A. gadovii 89, A. garmani 75, A. gemmosus 94, A. grahami 68, A. g. aquarum 73, A. gund- lachi 69, A. hendersoni 84, A. h. ravidor- mitans —, A. heteropholidotus 109 x, A. homolechis 78, A. h. cuneus ———, A. h. jubar ———, A. h. oriens ———, A. h. quadriocellifer ———, A. humilis 105, A. intermedius 99, A. isthmicus 89 x, A. kemptoni 104, A. krugi 79, A. lemurinus 104, A. limifrons 103 (Costa Rica), A. limifrons 99 (Pan.), A. lineatopus 69, A. lionotus 85, A. lividus ——, A. loysiana 89 x, A. luciae ———, A. lucius 84, A. mega- pholidotus 98, A. mestrei -——, A. monti- cola ———, A. nebulosus 100, A. nigro- lineatus 94, A. nubilus ———, A. occultus 100, A. oculatus ———, A. o. cabritensis ——, A. o. montanus ———, A. o. winstoni ——, A. olssoni 91, A. opalinus 82, A. ortoni 96 x, A. pachypus 101, A. penta- prion 81 x, A. peraccae 93 x, A. petersi +, A. pinchoti 90, A. poecilopus 96 x, A. polylepis 93, A. poncensis 87, A. por- catus 72, A. pulchellus 80, A. punctatus 88 x, A. p. boulengeri 103 m, A. quer- corum 89, A. quadriocellifer ———, A. richardi 81, A. ricordi subsolans X, A. r. viculus —, A. rodriguezi 101, A. roquet 77, A. rubribarbis ———, A. rupinae ———, A. sabanus ——, A. sagrei 73, A. s. stejnegeri 79, A. semilineatus 86, A. sericeus 90, A. smaragdinus 78 x, A. subocularis 76, A. stratulus 86 x, A. taylori 79, A. trachyderma 115, A. tropidogaster 96, A. tropidolepis 99, A. tropidonotus 81, A. uniformis 98, A. valencienni 86, A. villai 89, A. vittigerus 125 x, A. wattsi 87, A. woodi 87 x, Chamaeleolis chamaeleonides 99, Enya- lioides laticeps 108 m, Enyalius biline- atus ++, E. boulengeri +, E. catenatus X, E. iheringii ++, Polychrus marmora- tus 124 x, Urostrophus ornatus X. Because the lizards of the genus Ano- lis are numerous in species and often extremely abundant, much information has accumulated concerning their sexual size relationships. Schoener (1967) noted that in Anolis conspersus, isolated from other species on Grand Cayman Island of the West Indies, males are much larger than females, and are able to take larger prey items of different kinds, with the result that there is partial partition- ing of food resources between the sexes, and the potential carrying capacity of the habitat is increased. Later, Schoener (1970) discerned consistent patterns in the size relationships of insular West Indian species of Anolis of which there are several score. He found that wher- SEXUAL SIZE DIFFERENCES IN REPTILES 15 ever a small island is inhabited by a single species, that species is small-sized (often 40-70 mm snout-vent), with males much larger than females. Thus the rela- tionships found in A. conspersus were repeated in many other species. On is- lands that had two or more species, char- acter displacement in size occurred to varying degrees. Depending on the ex- tent of habitat overlap, species occurring in sympatry were altered from their size relationships in allopatric situations, be- coming less similar, with SSD reduced so that size overlap with competing spe- cies was minimized. Schoener found that in solitary kinds, the males col- lectively are larger than the males on the island having the richest anole fau- nas. With increasing species diversity, the species size distribution of males irregularly decreases in median, but in- creases in range of skewness. He found greater SSD in larger species. In a later study of mainland anoles I found (Fitch, 1976) correlation between climate and SSD; species living in rela- tively aseasonal climates of tropical rain forests or cloud forests tended to have the sexes nearly equal in size, or else the females were larger, but species liv- ing in sharply seasonal climates with drought or cold limiting reproduction to a concentrated short and stressful breed- ing season had males much larger than females (Table 6). In Anolis species, SSD has a range TABLE 6. Mean Female to Male Ratios (FMR) in Anolis. Num- Species ber Mean grouping oftaxa FMR at Range All species tested TOG: = 89:21)" =21.17 | (68-125) Insular species 48 80.90 +1.15 (68-100) Mainland species (all) 58 96.09 +1.35 (73-125) Humid tropical lowlands 29 100.41 +1.78 (81-125) Montane 15 97.27 +1.84 (87-110) Xeric 12 85.00 +2.12 (73-100) nearly as wide as that in all other liz- ards combined, with FMR from a mini- mum of 68 in A. grahami to 125 in A. vittigerus. Males are consistently larger than females in the insular species (mean FMR 81) whereas in about 40% of the mainland species females are larger (mean FMR 96). For 106 anole taxa FMR averages 89. It is noteworthy that no rainforest species of the mainland have males much larger than females. Similarly, in the giant rainforest anolines Enyalioides, Enyalius, Polychrus, and Urostrophus, females are relatively large. BASILISCINAE. Basiliscus basiliscus 78, B. vittatus 86, Corythophanes cristatus 109 x. In these amphibious and arboreal iguanids, SSD is large, and is accom- panied by marked dimorphism, with dor- sal crests developed in the male. Terri- toriality is highly developed in basilisks and males fight fiercely at times. In a study of Costa Rican populations of B. basiliscus, Van Devender (1978) found that SSD differed greatly, sometimes even between the populations of neigh- boring stream courses, and was highly responsive to such environmental factors as population density, and food supply. CroraPHYTINES. Crotaphytus collaris 93, Gambelia wislizenii 115. C. col- laris is a fairly typical iguanid, having the male markedly larger than the fe- male, territorial with bright colors and conspicuous display, whereas G. wislize- nii is highly atypical, having the female much larger than the male, and the male lacking territoriality and display. G. wislizenii is nomadic, and a lizard may wander widely rather than remaining in a small and relatively permanent home range or territory such as found in most iguanids. Wandering tendencies are probably correlated with predatory hab- its; in addition to insects, leopard lizards regularly prey upon smaller lizards such as Uta, Sceloporus, Phrynosoma and Hol- brookia. The large females are more saurophagous than the males. The allo- patric G. silus of the San Joaquin Valley 16 MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY in California differs from G. wislizenii in being largely insectivorous, in being ter- ritorial, and in having relatively large males. IcuANINAE. Amblyrhynchus cristatus 85, Conolophus subcristatus 91 x, Cte- nosaura similis 80, Cyclura carinata 82, C. cornuta 92, C. cychlura 93, C. pinguis 86, Dipsosaurus dorsalis 95, En- yaliosaurus clarki 93, Iguana iguana 91, Sauromalus obesus 92. These mostly large to giant-sized, mainly herbivorous and mainly tropical iguanids all have males larger than fe- males. Several of them have been sub- jects of intensive ecological and behav- ioral studies, which have indicated the following characteristics: there is a short and concentrated annual breeding sea- son; males are highly territorial, but many are subordinates that are denied territories because they cannot compete with the dominant adults. Subordinate males are often adolescents or small adults that have not yet attained their prime. Reproductive females may be crowded together in harems, or may be spaced because of mutual intolerance much weaker than that prevailing among the males. The latter fight fiercely at times, but most often rely on their stereo- typed displays to threaten or discourage potential rivals. PHRYNOSOMINES. Phrynosoma cornu- tum 107, P. coronatum 102 X, P. doug- lassi 110, P. modestum 112 x, P. orbicu- lare 103 x, P. platyrhinos 106, P. solare 108. The horned lizards are aberrant igua- nids. Males lack bright colors and spe- cial display organs. Territoriality seems to be lacking and display is weakly de- veloped. Whitford and Whitford (1973) found that individuals of P. cornutum often moved more than 100 meters in a day and frequently approached within one meter of another individual. Ordi- narily when such lizards became aware of each other, there was head bobbing and mutual retreat. In an exceptional instance observed on 19 July 1972, one lizard charged another that had ap- proached, bit it, and secured a hold, and the two fought intermittently for an hour and 10 minutes until they were separated by the observer. Fighting consisted of biting, scratching, and thrusting move- ments of the head by which the oppo- nent was jabbed with the occipital horns. Presumably the combatants were males, but their sex was not determined. De- spite this isolated observation, it seems clear that display and combat behavior are relatively weak in Phrynosoma com- pared with those in most other iguanids. The horned lizards are largely myrmeco- phagous. They are relatively slow-mov- ing and rely on their cryptic patterns and to a lesser extent on their spines for protection. Most of the species, includ- ing cornutum, coronatum, modestum, platyrhinos, and solare are oviparous, but douglassi and orbiculare are live-bearers. Broods in both the egg-laying and live- bearing species tend to be large com- pared with those of other iguanids of similar size. It is noteworthy that in all seven species investigated, females are larger than males, thus deviating from the usual trend in iguanids. SCELOPORINAE. Callisaurus draco- noides 89, C. d. rhodostictus 90, Hol- brookia maculata 108, H. m. approxi- mans 93 xX, Sceloporus adleri 92, S. bul- leri 97, S. chrysostictus 95, S. clarki 92, S. c. boulengeri 81, S. cozumelae 87, S. cyanogenys 105 x, S. formosus 103 x, S. graciosus 104, S. g. “gracilis” 103, S. g. vandenburgianus 95, S. grammicus 96, S. insignis 92, S. jarrovi 91, S. lundelli 105 x, S. magister 84, S. malachiticus 95, S. megalepidurus 99, S. merriami 95, S. m. annulatus 95, S. mucronatus 95, S. nelsoni 87, S. occidentalis 106, S. 0. bi- seriatus 107, S. olivaceus 111, S. orcutti 90, S. pictus 98 x, S. poinsetti 86, S. pyro- cephalus 85 x, S. scalaris 111, S. s. aeneus 99, S. s. bicanthalis 106, S. siniferus 86, S. smaragdinus 93, S. spinosus 99, S. tae- niocnemis 97, S. teapensis 93, S. torqua- tus 99 x, S. undulatus 110, S. u. conso- brinus 101, S. u. elongatus 112, S. u. SEXUAL SIZE DIFFERENCES IN REPTILES 17 erythrocheilus 110, S. u. garmani 107, S. u. hyacinthinus 107, S. u. tristichus 107, S. utiformis 93 x, S. variabilis 81, S. vir- gatus 112, S. woodi 106, Uma inornata 79, U. notata 79, U. scoparia 86, Uro- saurus ornata 97, Uta antigua 92, U. mearnsi 96, U. nolascensis 93, U. palmeri 91, U. squamata 93, U. stansburiana 87. This is a large group of xeric adapted, mostly ground living (or scansorial), me- dium- to small-sized iguanids that are best represented in southwestern North America. Males are usually larger than females, but there are many exceptions, especially in the large genus Sceloporus. In most there is strongly developed sex- ual dichromatism with males having bright colors that function in aggressive displays. These colors are most often concentrated on the sides of the ventral surface, where they are concealed when the animal is at rest, flattened against the substrate. In some species display colors and behavior are largely lacking, and males do not maintain territories. In an earlier report (Fitch, 1978) I have discussed SSD in the genus Sceloporus. Those kinds having relatively large fe- males were found to be characterized by a relatively large brood, single annual brood, small body size (< 60 mm S-V) and range in the Temperate Zone more often than by the opposite conditions. With few exceptions, most kinds of Sce- loporus having females larger than males occur in the United States, north of lati- tude 30°, whereas most kinds having males larger occur south of latitude 30° in southern Texas, Mexico or Central America. TROPIDURINAE. Ctenoblepharis nigri- ceps ——, Leiocephalus astictus 85, L. barhonensis ——, L. b. aureus ——, L. bs beatanus ——, Io.-b, oxygaster ———, L. cubensis 77, L. exotheotus 84, L. gigas 72, L. lunatus ——, L. |. arenicolor ——, L. l. melaenacelis X, L. 1. thomasi ——, L. macropus felinoi 70 m, L. pambasileus 78 x, L. paraphrus 76 x, L. personatus Sa. acitis. ——_ — Lm. jagraulus ——, L. p. budeni ——, L. p. mentalis ——, L. p. scalaris ——, L. p. tarachodes ——, L. p. trujilloensis ——, L. raviceps klin- kowskii 89 x, L. r. uzzelli 82, L. sierrae 66, L. stictigaster 83, L. vinculum —, L. v. altavelenus —, Liolaemus anomalus 91 x, L. archeforus 91, L. a. sarmentiori 94 m, L. constanzae —, L. fuscus —, L. kingii 92, L. lemniscatus —, L. magel- lanicus X, L. monticola X, L. nigroviridis =, Gupiotus Xx, plate, ——, L. tents X, Plica plica X, Plica umbra 91 m, P. u. ochrocollaris 97 m, Strobilurus torquatus +, Tropidurus albemarlensis 79, T. a. barringtonensis 84, T. bivittatus 78, T. delanonis 76, T. duncanensis 89, T. grayi 116, T. habeli 79, T. icae 87, T. occipitalis 81, T. pacificus 87, T. peruvianus 86, T. salinicola 92, T. stolzmanni 71, T. talarae 78, T. theresiae X, T. thoracicus 87, T. torquatus 80 x, Uracentron azureum X, U. a. guentheri X, U. a. werneri X, U. flaviceps 70 x, Uranoscodon supercili- osa X. In this South American and West Indian subfamily males tend to be much larger than females (Fig. 1), and have display coloration and behavior well de- veloped in connection with territoriality and courtship. An unexplained excep- tion to this trend is Tropidurus grayi of Charles Island in the Galapagos, having females larger. AGAMIDAE. Agama agama 86 m, A. agilis 87, A. atra ——, A. atricollis 89 x, A. cyanogaster ——, A. hispida 95 x, A. h. aculeata —, A. kirki —, A. mossambica ———, A. pallida 109, A. planiceps -—, A. tuberculata 93, Amphibolurus macu- losus 91, Calotes versicolor —, Draco melanopogon 106, D. quinquefasciatus 102, Goniocephalus modestus —, Japa- lura swinhonis 95, Leiolepis belliana —, Moloch horridus 113, Phrynocephalus ornatus X, P. scutellatus 105 m, Physig- nathus concinnus ——, Salea anamallay- Cide——, 5. norsield ——, The agamids are active, diurnal, visu- ally oriented lizards of Africa, Asia and Australia. Nearly all are oviparous. Vari- ous ecological studies of agamid species (Harris 1964, Mitchell 1973, Waltner 18 MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY fasciata -+4-, D. scabra 117 x. The African egg-eaters differ from other snakes in morphological features associated with their specialized feeding habits. Their relationships are uncertain. Females are relatively large. DipsADINAE. Carphophis vermis 117, Coniophanes bipunctatus ++++, C. fissidens 114, Diadophis punctatus 111, Dipsas catesbyi 96, D. pavonina —, D. variegata X, Ficimia olivacea 95 x, Ficimia quadrangularis 95, Geophis brachycephalus 117 m, G. hoffmanni 132 m, G. nasalis 105 m, G. rhodogaster 124 m, G. semidoliatus 129 m, Gyalopion canum 106, Hypsiglena torquata +++, Imantodes cenchoa 109 x, Leptodeira annulata 108, L. a. ashmeadi ++, L. a. cussiliris +++, L. a. rhombifera ++, L. frenata ++, L. nigrofasciata +, L. poly- sticta ++, L. punctata +, L. septentri- onalis +++, L. s. ornata +++, Pseustes poecilonotus +, Rhadinea brevirostris —, R. calligaster +++, R. decorata +, R. flavilata 112, R. fulvittis +, R. gaigeae ++, R. hesperis +++, R. laureata ++, Sibon dimidiata ———, S. nebulata X, S. n. leucomelas X, S. sanniola —, Sibyno- morphus mikani ++, S. ventrimaculatus +, Tantilla gracilis 126, T. melanoceph- ala +, T. planiceps 94 m, Tretanorhinus nigroluteus 141, Trimorphodon_biscu- tatus lambda 130 x, T. b. vandenburghi 127 m, T. b. lyrophanes +. The dipsadines are New World snakes that are mostly medium-sized or small, nocturnal and/or secretive-fos- sorial, predatory on invertebrates such as earthworms, slugs, snails, and _ soft- bodied insects, or on frogs, and in a few cases, on lizards or small snakes. Most are tropical. All are oviparous. Females were found to be larger than males in 16 of the 19 species for which series were available, but Sibon is an excep- tion to this general trend. FMR aver- aged 114.32 + 2.85. To my knowledge, male combat or rivalry has not been recorded in any dipsadine. DIsPHOLIDINAE. Dispholidus typus 102 x, Telescopus dhara ++++4, T. semiannulatus 128 x, Thelotornis capen- sis 100 x, T. kirtlandi +. These are ar- boreal African rear-fanged snakes, the boomslangs, large-eyed snakes and twig snakes. Females tend to be larger than males. GropipsaNnaE. Geodipsas depressiceps 116 x, Psammodynastes pulverulentus 109 x. The mock vipers and their relatives are rear-fanged terrestrial Old World snakes. Females are larger than males. In Psammodynastes there is color di- morphism in the sexes. HoMatopsinaE. Cerberus rhynchops 118 x, Enhydris chinensis +, E. bocourti +++4+, E. enhydris 109, E. plumbea +, Fordonia leucobalia 119 x, Homalopsis buccata 109. These heavy-bodied viviparous rear- fanged snakes occur in freshwater or estuarine habitats of southeastern Asia and the Indo-Australian Archipelago. They have usually been placed in a fam- ily separate from the Colubridae. Fe- males are consistently larger than males. HypropsinaE. Helicops angulatus ++. Like other groups of aquatic snakes, this Neotropical genus has females larger than males. LAMPROPELTINAE. Cemophora coc- cinea 79 x, Lampropeltis calligaster 91, L. getulus 87, L. g. boylii 95, L. g. hol- brooki 88, L. multicincta 112 m, L. py- romelana 91 m, L. triangulum 88 x, L. t. elapsoides 88 x, L. t. syspila 97, Rhino- cheilus lecontei 87 m, R. l. “clarus” 91 m, R. I. tessellatus ——, Stilosoma extenu- atum 104 m. In these oviparous North American constrictors males are usually larger than females (FMR averaged 91.5 + 1.90 for 13 taxa). Male competition and combat has been noted in various kinds of king snakes. An excellent ac- count of fighting in L. calligaster was that of Moehn (1967). Two males were 26 MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY found engaged in a “combat dance.” They were captured and caged together, and fighting continued intermittently over a period of days. It involved rear- ing and attempting to throw down the opponent with coiling and jerking move- ments, but also involved pursuit and vicious biting. LycoponTINnaE. Dinodon flavozona- tum 83 x, D. orientale 100 m, D. rufo- zonatum 96 x, Lycodon aulicus +, L. jara +, L. subcinctus +, L. travancori- cus +. These are nocturnal, oviparous, Asi- atic snakes; Dinodon species average con- siderably larger than those of Lycodon. The limited data available indicate that the females are larger in Lycodon, but males tend to be larger in Dinodon. LycopHipunaE. Lycophidion varie- gatum +, L. capense 133 x, L. laterale X, L. ornatum +++, L. semiannule X, Mehelya capensis ++, M. poensis ++++, M. savorgnanii ++, M. stenoph- thalmus ++++, Natriciteres olivacea 125ox. The wolf snakes, file snakes and marsh snakes of this subfamily are Afri- can and tend to nocturnality and to liz- ard- or frog-eating habits. To varying degrees the females are larger than the males. NatricinaE. Amphiesma beddomei ++, A. craspedogaster +, A. khasiensis +, A. modesta +++, A. monticola ++, A. platyceps —, A. popei X, A. pryeri ++, A. sauteri 116 x, A. sieboldi ++4, A. stolata 133, A. venningi +, A. vibakari X, A. xenura X, Aspidura copi +, A. trachyprocta ++++, Atretium schisto- sum 120 x, Balanophis ceylonensis —, Clonophis kirtlandi 110 m, Haplocercus ceylonensis X, Macropisthodon plumbi- color ++++, M. rudis 139 m, Natrix annularis 138, N. natrix 114 m, N. n. sicula 115, N. percarinata 136 x, N. tes- sellata 103 m, N. trianguligera 118, Nerodia cyclopion 124 m, N. erythro- gaster bogerti 107 x, N. e. transversa 115, N. fasciata 116 m, N. f. clarki +++4+4, N. f. confluens 132 m, N. f. pictiventris 152 m, N. rhombifera 111, N. r. blan- chardi 120, N. r. werleri 162, N. sipedon 132, N. s. insularum 108 m, N. s. pleuralis 124 m, N. taxispilota 117 m, N. valida 135, N. v. celaeno 109, N. v. isabelleae 142, N. v. thamnophisoides 121, Opistho- tropis latouchi +, Pseudoxenodon mac- rops —, P. nothus —, Regina alleni 106 m, R. grahami 120, R. rigida 134 m, R. septemvittata 114, Rhabdophis auricu- lata +, R. a. myersi ++, R. chrysarga 106, R. himalayana ++++4, R. nigro- cincta X, R. nuchalis ++++4+, R. sub- miniata 122, R. tigrina 120, Rhabdops bicolor +, Seminatrix pygaea 110, Store- ria dekayi texanum 120, S. d. victa 120, S. occipitomaculata 118, Thamnophis brachystoma 112 m, T. butleri 109, T. couchi 132 m, T. c. gigas 134 m, T. c. hammondi 136 m, T. c. hydrophilus 130 m, T. cyrtopsis 146 m, T. elegans 118 m, T. e. biscutatus 138 m, T. e. terrestris 106 m, T. e. vagrans 122, T. eques 115 x, T. marcianus 126 m, T. ordinoides 125, T. proximus 110, T. radix 108 m, T. rufi- punctatus ++, T. sauritus 118, T. sirtalis 114, T. s. parietalis 123, T. s. pickeringi 124, Tropidoclonion lineatum 122, Vir- ginia striatula 116, V. valeriae 124, Xeno- chrophis cerasogaster 153 x, X. piscator 135, X. punctulata ++, X. vittata 124, Xylophis perroteti ++. This large subfamily of holarctic colubrids, including the water snakes, garter snakes and their relatives, are ac- tive, diurnal or nocturnal, and many have aquatic or wetland habitats. They are mostly medium-sized or small, and feed on a variety of vertebrate and in- vertebrate prey, but especially on fish. In general, members of this group are “r-selected,” with rapid development, large clutches or litters and rapid pop- ulation turnover. All species in the nine North American genera are live-bearers, whereas the much more diverse Asiatic species are oviparous, with the single exception of Natrix annularis. Regard- less of these differences, it is a general rule that females are larger but Pseu- doxenodon is an apparent exception. In SEXUAL SIZE DIFFERENCES IN REPTILES 27 63 taxa for which definite figures were available, FMR averaged 122.05 = 1.52 (Fig. 4). It averaged 122 for 20 kinds of Thamnophis (Table 7) and 124 for 13 kinds of Nerodia. In various natricines mating aggregations have been observed, with complete lack of male rivalry. Sev- eral males may simultaneously court the same female, their massed bodies form- ing a “snake ball.” With no rivalry or combat between males, large male size would confer no selective advantage, but large size in the female enables her to produce a relatively large clutch or litter. Primiparous females are much smaller and less prolific than others, but successive broods become progressively larger as the female gains in bulk. TABLE 7. Mean Female to Male Ratios (FMR) in Thamnophis. Num- Species ber Mean grouping of taxa FMR o" Range All species tested 20 122.30 +2.50 (106-146) Aquatic species 6 136.00 +2.31 (130-146) Marshland species 9 118.00 +2.31 (108-126) Terrestrial species 5 114.00 +3.38 (106-125) SAMPLES Seay, OF TAXA 70 80 90 FMR NornopsInaE. Ninia maculata 107 Although the Australian protero- glyphs are no longer considered elapids, the group still includes highly diverse genera of American, African and Asiatic snakes, and may be polyphyletic. Within the group, medium to large size and snake-eating habits are common. All ex- cept Hemichatus are oviparous. In He- michatus FMR is especially high, and for the group as a whole the usual con- dition seems to be that of having the females larger. The Asiatic coral snakes and kraits, Bungarus and Calliophis, are exceptions, having males larger than fe- males. The primitive oviparous seasnakes or “sea kraits” of the genus Laticauda are now considered elapids not closely SEXUAL SIZE DIFFERENCES IN REPTILES 29 related to hydrophiine seasnakes (Smith et al., 1977). In Laticauda females are larger than males. HYDROPHIIDAE. This family is now construed to include not only the true sea snakes (hydrophiines) but also the primitive terrestrial Australian pro- teroglyphs that have formerly been con- sidered elapids (oxyuranines; Smith et al., 1977). The two subfamilies are much different ecologically, and their repre- sentatives are therefore listed and dis- cussed separately. HypropHuNnakE. Astrotia _ stokesii +++, Enhydrina schistosa 111 x, Hy- drophis brookei X, H. caerulescens —, H. cyanocinctus ++, H. fasciatus —, H. klossi +, H. lapemoides X, H. mammil- laris X, H. obscurus +, H. ornatus —, H. spiralis +, H. stricticollis X, H. tor- quatus 97 x, Kerilia jerdoni 103 x, La- pemis curtus 100, Microcephalus cantoris ++, M. gracilis +, Pelamis platurus 118, Praescutata viperina —, Thalassophis anomalus —. The sea snakes are medium-sized to large viviparous, marine, fish-eaters. Compared with terrestrial snakes they are less prolific, having only one or two young at a birth in some instances. Even in the tropical climates where most oc- cur, there is a brief annual breeding sea- son. Large-scale mating aggregations have been observed (Smith, 1943). Ap- parently mating is promiscuous in these aggregations. There are no records of male competition or combat. Of the 20 species for which informa- tion is available, five apparently have males larger than females, five have the sexes about equal and 10 have females larger than males. Large series are avail- able to compare sizes of the sexes only in Enhydrina schistosa, Lapemis curtus and Pelamis platurus. In the latter spe- cies Kropach (1975) found a mean length S-V of 452 mm in 359 males and 481 mm in 391 females, FMR 109, but the series included immatures as well as adults. Kropach also listed the lengths of 100 of the largest individuals and found 70 were females. Means for the 30 largest of each sex were utilized to calculate FMR of 118. OxyuRANINAE. Acanthophis antarc- ticus 131, Austrelaps superbus 92, Caco- phis kreftii 112, C. harriettae 125, C. squamulosus 129, Hemiaspis signata 99, Notechis scutatus 99, Pseudechis por- phryriacus 95, Urechis gouldi 83, Vermi- cella annulata 139. The Australian proteroglyphs, per- haps more than any other snakes, are noted for male combat. Worrell (1964) described this behavior as follows: Coinciding with the mating season is the spectacular wrestling of the males . . .. One or more males may pursue each other over rocks, through creeks and scrub, twining around each other, wrestling and crawling frenziedly about the bush, flattening the grass as they writhe, and stopping occasionally to lift their forebodies high, swaying nervously. It is significant that of the species checked, only those of the small secre- tive Cacophis and Vermicella and the sluggish, viperlike Acanthophis were found to have females larger than males. Male combat has not been observed in these two genera, and probably does not occur. Shine (1980c) emphasized the viperlike appearance, behavior, and re- productive and feeding strategy of the Australian death adder as a case of evolutionary convergence. VIPERIDAE. Atheris nitschei ++, A. squamiger 113 x, Bitis arietans 93, B. caudalis X, B. cornutus ——, B. gabon- ica --1-,. B- nasicormmis: 4, B. patict- squamata +, B. peringueyi ++, Causus defilipii X, C. lichtensteini 115 x, C. lineatus +, C. resimus +, C. rhombeatus 95 x, Cerastes cerastes 120 x, Echis cari- nata 129 m, E. colorata 98, Pseudoceras- tes fieldi 108 x, Vipera ammodytes 118 m, V. berus 108, V. latastei 90 x, V. super- ciliaris +, V. ursini 110, V. xanthina 95. These are venomous front-fanged snakes of Africa and Eurasia. Most are heavy-bodied and slow-moving, securing their prey by ambush and the venomous 30 MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY bite. For 13 species FMR averaged 107 (90-129). Most species have females larger than males, and most are vivipar- ous, producing medium to large litters. Relatively large size of the female makes possible the production of large litters. However, there is male combat in vipers, and in fact males of Vipera berus are known to be territorial. In a study of the diminutive V. ursini, Bruno (1967a) found that FMR increased from 104 in Yugoslavia to 105 in Italy and 110 in France. The Yugoslavian vipers were found to be the largest and the Italian were the smallest. St. Girons (1978) noted that the sexes are about the same size in Vipera aspis and probably in V. kaznakovi, whereas males are the larger in V. ammodytes and females are larger in V. berus, V. seoanei and V. ursini. All these are small vipers of cold and temperate climates of Europe and Asia. CROTALIDAE. Agkistrodon acutus +, A. blomhoffi brevicaudus X, A. b. siniticus X, A. caliginosus X, A. cognatus —, A. contortrix 94, A. halys 112 x, A. himalayanus X, A. piscivorus 96, A. rho- dostoma +++, A. saxatilis —, Bothrops atrox 115, B. bilineatus +++, B. lans- bergi 101, B. nasutus 96, B. neuwiedii X, B. pulcher 153 x, B. punctatus 144 x, B. schlegelii 111, Crotalus atrox 91, C. cerastes 103, C. durissus 88, C. d. ter- rificus 97, C. enyo 92, C. horridus 94, C. lepidus 82 x, C. 1. klauberi 85, C. luca- sensis 87, C. mitchelli 94, C. m. pyrrhus 78, C. m. stephensi 88, C. molossus 91, C. m. nigrescens 84, C. pricei 82, C. ruber 84, C. scutulatus 88, C. tigris 82, C. triseriatus 90, C. viridis 92, C. v. con- color 88, C. v. helleri 80, C. v. lutosus 90, C. v. nuntius 78, C. v. oreganus 87, Hypnale hypnale ++, H. walli —, Sis- trurus catenatus 92, S. ravus exiguus 76 x, Trimeresurus albolabris 161 x, T. can- toris ++++, T. elegans X, T. erythrurus ++++4+, T. flavomaculatus ++++, T. flavoviridis 89, T. gramineus +++, T. jerdoni ++, T. kaulbacki +, T. labialis +, T. macrolepis ++++, T. malabaricus +++, T. microsquamatus X, T. monti- cola ++++, T. okinavensis 99, T. puniceus 139 x, T. purpureomaculatus +++4+, T. stejnegeri 109 x, T. strigatus +, T. tokarensis ——, T. trigonocephalus 4+, 2. waglert X. The pit vipers are now generally con- sidered to be a subfamily of the Viperi- dae. These New World and Asiatic sole- noglyphs are mostly medium-sized to large, heavy-bodied and slow-moving ambush hunters, predatory on verte- brates. They rely on potent venom to subdue the prey. Most are live-bearers, but a few Asiatic species of Agkistrodon and Trimeresurus as well as the Neo- tropical Lachesis are oviparous. In most species of Trimeresurus females are markedly larger than males, but males are larger than females in 24 of 25 kinds of rattlesnakes. The exception is Cro- talus cerastes in which FMR is 103 and for the entire group FMR averages 87.6 + 1.19 (Table 10). Females are relatively small in C. mitchelli pyrrhus (77) and C. viridis nuntius (78) whereas in C. molossus nigrescens the ratio is near parity (99). There is no obvious corre- lation with body size, nor with climate. Rival male rattlesnakes approach each other, rear with their ventral surfaces in contact, and with sudden jerky mo- tions each attempts to throw down its opponent. The larger and heavier snake is usually the winner but sometimes only after a prolonged bout; the loser with- draws from the encounter and leaves the area. Large size in the male would seem to confer selective advantage. Whether some species of rattlesnakes are more in- clined to rivalry and combat than others is still unknown. In the copperhead Agkistrodon con- tortrix and the cottonmouth A. piscivo- rus, the FMRs 93 and 96 were similar to those found in rattlesnakes. Both these species are known to have a com- bat dance, similar to that of rattlesnakes except in details. Whether the same ap- plies to the Asiatic species is not known, but published figures on maximum sizes indicate that in some of them the fe- SEXUAL SIZE DIFFERENCES IN REPTILES 31 males are the larger including A. blom- hoffi siniticus, A. acutus and A. halys. Males are the larger in A. halys cognatus, A. saxatilis and A. blomhoffi brevicaudus, while in A. caliginosus the sexes seem to be equal. In the Asiatic Hypnale walli males are the larger. In the Neotropical Bothrops and the Asiatic Trimeresurus females are usually much larger than males. Crocodylia CROCODYLIA. Alligator mississip- piensis 82, Crocodylus niloticus 85. The alligator was studied in Louisi- ana by Chabreck and Joanen (1979) from 2500 young captured, marked and re- leased, and 218 recoveries, some after attainment of adult size. The data indi- cated that in both sexes growth con- tinued long after sexual maturity, but at reduced rates, slowing earlier and more abruptly in the female. The following average total lengths in meters were cal- culated or projected: 10-year-olds males2.55 females 2.10 20-year-olds males3.50 females 2.55 oldest males 4.2 females 2.73 At the age of ten years, both males and females were sexually mature but still growing rapidly; at age 20 females were near their maximum size but males were still capable of substantial gain. FMR was 82 for 10-year-olds, 73 for 20- year-olds and 65 for the oldest. The lat- ter is one of the lowest FMR figures recorded for reptile species. Cott (1961) indicated the following total lengths and weights for mature Crocodylus niloticus: Males (14) 3.416 m (3.073-3.743) 170.8 kg (115.8-240.0) 2.911 m (2.600-3.192) 104.2 kg ( 70.2-146.2) In this crocodile SSD is large, but less than in Alligator mississippiensis. Prob- ably males are substantially larger than females in most crocodilians, with simi- lar trends of widening SSD with advanc- ing age, but definite figures are not Females (50) available. Staton and Dixon (1977) in a study of Caiman crocodylus observed instances of coitus in which males ap- peared to be 1.7 to 2.5 m in length and females 1.2 to 1.5 m. However, Brazaitis (1973) noted that in the small Alligator sinensis the female is larger than the male. Presumably this was mentioned because it is the exception, and size re- lationships of the sexes were not indi- cated for other kinds of crocodilians in Brazaitis’ review. Crocodilians are known to maintain territories, and male aggression and com- bat are common. Garrick and Lang (1977) compared social behavior in Alli- gator mississippiensis, Crocodylus acutus and C. niloticus. They found that in all three species combat between males con- testing for dominance precedes the es- tablishment of mating territories. Voice is prominent in social behavior. Both sexes “bellow,” especially in the breed- ing season. The bellowing alligator is usually in the water. The sound is ac- companied by stereotyped movement with raising of the head and arching of the tail, and, in the male, eversion of the submaxillary gland. Bellowing sig- nals the presence and location of the in- dividual as a member of a social group (Garrick, Lang and Herzog, 1978). Ter- ritorial males dominate the breeding groups. In A. mississippiensis alpha males have been observed to interrupt courtship of subdominants. Females show submissive behavior in the pres- ence of territorial males but may form dominance hierarchies among them- selves. They move freely from one male’s territory to another. Selective factors which might tend to increase female size in crocodilians are: (1) large clutch size, and the need to increase the capacity of the female; (2) Cannibalistic predation on the de- pendent young, and the need for mater- nal defense against other adults, includ- ing males. Factors which might select for increased male size are direct com- petition for females, or for breeding ter- 32 MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY ritories, and the existence of social hierarchies. Stress associated with breed- ing and competition for mates is intensi- fied because it is concentrated in a relatively short breeding season in all species. DISCUSSION Extensive sampling, comparing sizes of the sexes in many species of reptiles, has demonstrated SSD to be extremely labile within the class. Females ranged in size from just over one-fourth to about 15 times male bulk in a virtual con- tinuum. Within each of the main groups, turtles, lizards and snakes, also, was found a wide range of SSD, and to a lesser degree the same statement applied to families, subfamilies and genera (Tables 8 to 11). Even individual species proved to have important differences in SSD from one population to another, and seemingly SSD is highly susceptible to selective pressure bringing about evolutionary change. Also, direct en- vironmental influences may alter SSD. In turtles and snakes it is most com- mon for females to exceed males in aver- age size, whereas in lizards the opposite relationship is more common. However, in each group many exceptions from the general trend are found and these aid in identifying some of the factors which were the basis for natural selection pro- ducing sexual size differences. Rivalry and aggression in males promote selec- tion for large individuals of that sex; selection for large clutches or litters, and for relatively large neonates may result in selection of relatively large females. The seven reptile species noted as having the lowest FMRs, 70 or less (min- imum 66) are all insular West Indian iguanids, Anolis (5 species) and Leio- cephalus (2 species). It has already been shown under the discussion of Anolis, that relative size of females averages markedly smaller in the insular species than in those of the mainland. This con- dition is associated with generally high population densities, light predation pressure, and intense intraspecific com- petition in the insular species. Diver- gence in sizes of the sexes alleviates intraspecific competition for food (Schoe- ner, 1967). One of the seven species with lowest FMR, Anolis lineatopus (FMR 69) of Jamaica has been the subject of an in- tensive ecological study (Rand, 1967). These findings are of special interest TaBLE 8. Distribution Of FMR Percentages Within The Turtles, Lizards, Snakes And Major Families Of These Groups. Female length as percentage of male length (FMR) Num- ber of 101- 111- 121- taxa <80% 80-89% 90-99% 100% 110% 120% 130% >130% Total Turtle 50 - 4% 18% 8% 20% 8% 2% 40% 100% Emydid 28 - — 11% 71% 14% 11% - 57% 100% Lizard 40S 11% 21% 33% 2% 27% 6% 1% - 100% Geckonid 43 - % 26% % 51% 9% - - 100% Iguanid 226 =. 200% 27.5% 31% 1% 17% 2.5% 1% = 100% Agamid ip, — 25% 34% - 33% 8% - ao 100% Lacertid 3H) _ 19% 56% % 16% 6% — _ 100% Teiid 38 3% 18% 37% % 29% 5% 3% - 100% Scincid 51 2% 8% 26% % 46% 14% - - 100% Snake 278 2.5% 11.5% 19% % 19% 20.5% 12% 12% 100% Colubrid 214 — 7.5% 14% 3% 19.5% 22.5% 14% 12.5% 100% Elapid-hydrophiid 21 - 9% 33% % 10% 19% 10% 4% 100% Viperid 1s = = 38% = 23% 31% 8% = 100% Crotalid 41 % 34% 34% — 8% 7% — 10% 100% SEXUAL SIZE DIFFERENCES IN REPTILES 33 because A. lineatopus is suspected to be representative of various other lizards that have relatively large males and small females in its social system and reproductive strategy. As in other anoles, the females lay one egg per clutch, but oviposition is frequent and breeding oc- curs throughout the year. Hatchlings are intolerant of each other and from the start they space themselves and de- fend territories. However, they avoid adults and are subject to cannibalistic predation. Individuals of both sexes and all sizes are territorial, but agonistic be- havior is directed mainly against similar- sized individuals. Hence, territories may overlap extensively. An adult female may have several mutually exclusive ju- veniles living within her territory. Small lizards avoid larger ones, and are gen- erally ignored or sometimes briefly chased by them. A male’s territory may encompass those of several females and he may mate with them regularly. Males spend much of their time in territorial display. One male observed for an en- tire day displayed on the average, every 3.5 minutes. However, there is little pre- copulatory display or courtship. Females are individually recognized. Mating oc- curs when an approached female is re- ceptive and does not move away to avoid the male. Nonreceptive females flee and escape the male easily. Imma- ture males may compete with similar sized females for territories. Also, they may be treated as females by courting adult males, but invariably flee from the male’s approach. On the average males use larger and higher perches than do other individuals. Although displays usu- ally serve to maintain territorial spacing, rival males fight fiercely at times. Com- bat usually involves threatening ap- proach, sparring, and biting with jaws interlocked. Usually one combatant is thrown from perch to ground. Combats usually are brief and do not result in serious injury to either participant. Forty-four additional species of rep- tiles were found to have notably low FMRs in the range from 71 to 80. These included seven species of snakes (Cro- talus, Coluber, Cemophora, Drymoluber, Psammophis, Sistrurus) but were mostly lizards. The latter included a_ skink (Scincus) and a teiid (Cnemidophorus) but otherwise were all iguanids, espe- cially species of Anolis (15 insular, 5 mainland), Leiocephalus (4 insular) and Tropidurus (4 insular, 3 mainland), but also including Uma (2) and Ctenosaura (1). For some of these species habits are little known, but a few have been sub- jects of intensive field study. In an early study of Anolis sagrei (FMR 79) in Cuba, Evans (1938) described territoriality and TABLE 9. Distribution Of FMR Percentages Within Major Subfamilies Of Iguanid Lizards And Colubrid Snakes. Female length as percentage of male length (FMR) Num- ber of 101- 111- 121- taxa <80% 80-89% 90-99% 100% 110% 120% 130% >130% Total Iguanidae 226 20% 27.5% 31% 1% 17% 2.5% 1% ~ 100% Anolinae 115 26% 28% 21% 2% 17% 4% 2% ~ 100% Iguaninae 11 - 36% 64% - - - - 100% Sceloporinae 62 3% 18% 50% - 23% 6% - — 100% Tropidurinae 33 ©633% 42% 18% - - 3% = = 100% Colubridae 214 - 7.5% 14% 3% 19.5% 22.5% 14% 12.5% 100% Alsophiinae 14 - 1% 14% - 14% 29% 71% 29% 100% Colubrinae 36 8% 14% 33% 8% 33% _ 3% - 100% Dipsadinae 20 - - 20% - 20% 25% 25% 10% 100% Lampropeltinae 13 8% 38% 38% - 8% 8% - - 100% Natricinae 66 _ - - = 18% 35% 20% 27% 100% 34 MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY male fighting. He found a social system in which dominant adult males main- tained large territories supporting vari- ous other categories of individuals in- cluding juveniles, breeding females, and subordinate males. Michael (1972) stud- ied the ecology of Anolis carolinensis (FMR 79) in eastern Texas. He found that most females begin to ovulate in the season following their own hatching. Although males attain sexual maturity early, when they are less than a year old, still relatively small, and lacking full development of their secondary sexual TABLE 10. Mean Female to Male Ratios (FMR) For Species In Various Genera Of Lizards And Sphaerodactylus 7 107.00 +1.90 ( 99-113 Thamnophis 20 122.30 +2.50 (106-146 Tropidurus 16 84.38 +2.52 ( 71-116 Snakes. Num- ber of Mean Genus taxa FMR om Range Anolis 106 89.21 +1.17 ( 68-125 Cnemidophorus 12 93.08 +1.79 ( 79-104) Crotalus 25 87.60 +1.19 ( 78-103) Elaphe 9 99.00 +2.24 ( 86-108) Eumeces 14 99.93 +1.11 ( 90-106) Lacerta 22 96.27 +1.97 ( 82-116) Lampropeltis 9 93.10 +2.64 ( 87-112) Leiocephalus ll 78.36 +2.12 ( 66- 89) Mabuya 16 101.56 +2.42 ( 87-120) Nerodia i 25.1 238i 107-162) Phyllodactylus 12 101.25 +1.48 ( 95-115) Sceloporus 49 97.96 +1.23 ( 81-112) ) ) ) characters, nearly all matings involve the relatively few large and dominant males that are at least 36 months old and 60 mm S-V. In Cnemidophorus lemniscatus (FMR 79) males are more brightly col- ored than females, and are known to be fierce fighters. Ctenosaura similis (FMR 80) also has a polygynous mating system, with large dominant males having relatively large territories which may each include the territories of several females. The latter are mutually exclusive, but the females are less agonistic than males. Immature or subordinate adults may have terri- tories within those of other individuals. Ctenosaura is an exception to the rule that most reptiles that have relatively small females have small egg clutches (e.g., only one egg in Anolis). A large female ctenosaur may lay more than 80 eggs; average clutch was found to be 43 (Fitch and Henderson, 1978). The snakes that have exceptionally low FMRs are rattlesnakes, and colu- brids of two subfamilies. The spectacu- lar combat dance of the rattlesnakes is well known. Many of the field observa- tions of it pertain to Crotalus mitchelli and C. viridis, the two species having the lowest FMR (78 in both C. m. pyrrhus and C. v. nuntius). The ex- istence of male combat in Drymoluber dichrous (FMR 74) and Psammophis TaBLeE 11. Distribution Of FMR Percentages Within Various Genera Of Snakes And Lizards. Female length as percentage of male length (FMR) Num- ber of taxa <80% 80-89% 90-99% Anolis 106 28% 29% 21% Cnemidophorus 12 % 4% 67% Crotalus 25 8% 54% 33% Eumeces 14 - - 43% Lacerta 22 - 24% 41% Leiocephalus 14 36% 36% 28% Mabuya 16 - 19% 19% Nerodia i - - - Phyllodactylus 12 - - 31% Sceloporus 49 = 17% 48% Thamnophis 20 Tropidurus 16 38% 50% 6% 101- 1ll- = 121- 100% 110% 120% 130% >130% Total % 18% 1% 1% - 100% - 25% - - - 100% - 4% - - - 100% - 57% - - - 100% 4% 24% 9% - - 100% - - - - - 100% - 43% 19% - - 100% - 18% 29% 18% 35% 100% 23% 38% 8% - - 100% - 27% 8% - - 100% - 20% 25% 30% 25% 100% - - 6% - - 100% SEXUAL SIZE DIFFERENCES IN REPTILES 35 schokari (FMR 79) may be suspected. Social interactions between snakes are much less often observed than those of lizards. Aggressive behavior has been reported in relatively few kinds but per- haps occurs in many others. Presumably those males that are most aggressive and most successful in vanquishing rivals in the combat dance are also most success- ful in mating, but this relationship has not actually been demonstrated in field studies. The possibility of males siring off- spring by forcible mating may have led to selection for larger size in the male. Even a small difference in size between the sexes with the male larger and stronger, might greatly increase the pos- sibility of rape. In a species having the female larger, she would tend to domi- nate and intimidate the male; he could not overpower her and rape would scarcely be possible. Thornhill (1980) has developed the theory that large male size has evolved in many species, in- cluding humans, to make rape possible. He rejected the idea that sexual di- morphism in humans was related to an evolutionary history in which the preva- lent mating system was harem polygyny, but “. .. regardless of the prevalent mat- ing system in human evolutionary his- tory, larger males were favored because of the increased likelihood of successful rape if they failed to compete success- fully for parental resources.” In both snakes and turtles the highly altered body form renders copulation difficult, and even though the male suc- ceeded in overpowering the female, he might not be able to accomplish intro- mission. In both groups female coopera- tion seems essential for consummation of courtship to occur. A female tortoise may frustrate the male’s attempts merely by resting her shell on the substrate in- stead of standing, and a female snake must raise her tail causing the cloaca to gape for the male’s hemipenis to be in- serted. In contrast, lizards accomplish copulation much more readily. Seem- ingly forcible copulations, including homosexual matings with subordinate or defeated males, are fairly common. It may be significant in this connection that the male is the larger in the ma- jority of lizard species, whereas the re- verse is true in the majority of snakes and turtles. Predation may be an important in- hibition to the development of male combat and the evolution of relatively large males. In discussing sexual size differences in amphibians, Shine (1979) wrote that . a major factor in the evolution of male combat may be the participant’s vulnerability to predation. Fighting frogs are exposed to predators . . . and one might expect combat to be most common in species that are at little risk. Risk should be lowest in species with large body size or chemical de- TENSES 2a:c Presumably the same factors affect sex- ual size ratios in reptiles. In snakes, especially, male fighting and relatively large male size are characteristic of for- midably venomous kinds—rattlesnakes and their near relatives, and the Aus- tralian oxyuranines. Although none of these snakes is free from predation, they are certainly much less vulnerable than non-venomous types, and hence can in- dulge in fighting with reasonably low risk of predation. Male fighting and relatively large male size is also con- spicuous in the crocodilians, giant rep- tiles which as adults are generally secure from predation. In lizards, on the contrary, male fighting and relatively large male size is common and occurs mostly in kinds that are not large or formidable and lack noxious qualities—lacertids, teiids and iguanids (especially anolines and tropidurines) that are highly vulnerable to predation. A common trait of these species is that they are active, agile and swift. A combat or chase may be almost instantaneous, and exposure to predation is thereby minimized for any single en- counter. Likewise, in snakes, several of 36 those that have relatively large males and are known or presumed to have male combat are relatively innocuous but fast-moving kinds, Coluber and Psammophis. A group of 120 species (87 lizards, 31 snakes, 2 turtles) were found to have FMRs in the range 81-90, that is, with males substantially larger than females. In this group, 60 were iguanids in 10 genera, but Anolis was by far the best represented, with 33 species. Other liz- ards were geckonids (2 genera), agamids (1 genus), teiids (4 genera), lacertids (3 genera) and skinks (3 genera). The 31 snakes belonged to 13 genera of colu- brids, elapids and crotalids; Crotalus with 13 species and Lampropeltis with 4 species were the best represented. At the upper end of the scale, with FMRs exceeding 130, that is with fe- males very large, are 37 species of snakes \ PERCENTAGES OF TAXAIN SAMPLES 60 80 100 I20 | I40 MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY and 20 turtles (Fig. 5). All the turtles are emydids and trionychids. Species of the genera Graptemys and Trionyx were found to have FMRs much higher than in any other reptils. The snakes include a boid, 2 typhlopids, 17 natricines, 4 alsophiines, 7 other miscellaneous colu- brids, 2 oxyuranines and 2 crotalids. The group with somewhat smaller FMRs, in the range 121 to 130, was found to include 30 snakes and only 2 lizards, the latter both rainforest igua- nids, Anolis vittigerus and Polychrus marmoratus. The snakes included a boid, a typhlopid, a viperid, 2 oxyuranines, 12 natricines, 4 dipsadines, and 9 other mis- cellaneous colubrids. In the FMR range 111 to 120 were found 26 species of liz- ards of eight families, Ablepharus (2), Anolis, Chamaeleo, Coleonyx, Gambelia, Ichnotropis, Lacerta (2), Lipinia, Mabuya (3), Moloch, Ophiomorus (2), Phyllodac- I6O 180 200 220 FMR (% FEMALE TO MALE LENGTH S-V) Fic. 5. Comparison of FMR in turtles, lizards and snakes. Each group has a wide range of FMR but trends differ with turtles attaining much higher ratios than squamates, and snakes attaining much higher ratios than lizards. SEXUAL SIZE DIFFERENCES IN REPTILES 37 tylus, Ptychodactylus, Sceloporus (4), Sphaerodactylus (2), Tropidurus, Xan- tusia, and 63 other species of snakes of 42 genera. More than half of the reptile taxa studied had FMRs in the range 91 to 110, that is with small or moderate size difference between the sexes, but only about 3.2 percent of the total 770 lacked SSD. Regardless of which sex is larger, the lizards and turtles in this range usu- ally have male rivalry and combat. In the snakes, on the contrary, combat is known to occur mostly in those kinds having males definitely larger than fe- males. Significant trends in the correlation of FMRs with other specific traits are discernible in a few instances. Other such correlations are suspected but are still not demonstrable. In general, rela- tively large female size is demonstrably correlated with: (1) viviparous (vs. ovip- arous) reproduction, (2) large (vs. small) mean number of offspring in clutch or litter, (3) temperate (vs. tropical) climate where the species occurs, and (4) small (vs. large) body size. All these factors are interrelated. There are many species that are exceptions to the general trends. According to Trivers’ (1972) theory, intrasexual competition is closely linked with parental investment. Whichever sex (usually the female) devotes the most energy, risk and sacrifice to the offspring will be in short supply, and will be the object of competition by the opposite sex. Intrasexual competition will select for size, strength and aggressiveness, and the most successful competitors will have many mates and disproportionately large numbers of offspring. Figure 6 demonstrates the trend from few eggs or young per clutch or litter in species having relatively small fe- males to much larger broods in those species having relatively large females. Anoles and geckos make up a high pro- portion of the small-brooded species in this particular sample, whereas many of the large-brooded species are natricine snakes. Striking exceptions to the gen- eral trends are seen in Ctenosaura similis and Iguana iguana, which have relatively small females, yet these produce large clutches, with more eggs than other liz- ards and more than most snakes. Figure 7 demonstrates the trend in squamate reptiles from a low incidence of viviparity in those species having rela- tively small females to a high incidence of viviparity in those having relatively small males. Viviparous species are com- mitted to a strategy of relatively long intervals between broods during gesta- tion, compensated by moderate or large numbers of young per brood. As a con- tainer and carrier of the eggs and em- bryos, the female is subject to selective pressure to attain adequately large size. Figure 8 demonstrates the related trend in squamates from a high percent- age of tropical species among those with relatively large males to a minority of tropical species (i.e., mostly temperate zone species) among those with rela- tively large females. The most plausible explanation of this trend is that tropical species, having continuous breeding in some instances, or at least having an extended breeding season, are under less selective pressure to increase their size as egg containers than are those more restricted to a short and concentrated breeding season in the temperate zone. Figure 9 shows mean sexual size ra- tios in lizards and snakes of various body-size groups. The main trend seems to be from larger mean size in the groups of species having relatively large males to smaller mean size in the groups of species having relatively large females. However, some points on the graph de- viate from the general trend. Also each FMR grouping includes species over a wide size-range, and the correlation be- tween FMR and body size is not sta- tistically significant. Both Ralls (1976) and Kolata (1977) after examining the evidence, mainly in mammals and birds, concluded that no one of the current theories could satis- 38 MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY NUMBER OF EGGS OR YOUNG PER LITTER OR CLUTCH 80 lOO I20 I4O I6O FMR (%FEMALE TO MALE LENGTH SV) Fic. 6. Correlation of mean number of offspring per brood with FMR in 505 taxa of squamate reptiles showing trend from few young in kinds having relatively large males to many young in kinds having relatively large females. For each sample, mean, range, standard deviation, and two stand- ard errors on each side of the mean are shown. Major sources of information on brood size were: Fitch 1970, Kopstein 1941, Pope 1935, and Wright and Wright 1957, but many others also were utilized. For some of the taxa that were included, only one record of a brood was available. factorily explain all instances in which sexual size differences exist as each case is somewhat different, and the important effects of ecological and physiological factors have to be taken into account. The records herewith accumulated for reptiles certainly support the supposi- tion that the sources of sexual size differ- ences are complex and varied. Freshwater turtles have progressed farthest in evolving disparate sizes in the sexes, with females commonly 1.4 to 1.8 times the linear dimensions of males and 3 to 6 times their bulk (Dei- rochelys, Graptemys, Pseudemys, Chry- semys and Trionyx). In all of these, time to maturity is accelerated in males as compared with females. Usually the male’s development from hatching to sexual maturity occurs in from 50 to 60 percent of the time required by the female. The result should be an excess of males, and the production of females so large and bulky that they are rela- tively safe from natural enemies and are able to utilize certain food resources SEXUAL SIZE DIFFERENCES IN REPTILES 39 IN SAMPLES PERCENTAGES OF VIVIPAROUS SPECIES 80 loo FMR (% FEMALE TO MALE LENGTH S-V) 120 I40 I60 Fic. 7. Correlation of oviparity with relatively large male size vs viviparity with relatively large fe- male size in 609 species of squamate reptiles. not available to the males. Sex ratios of several of these species approximated 1:1 in field samples (Bury, 1979). In a re- cent study of Graptemys geographica at Lake of Two Mountains, Quebec, Gor- don and MacCullock (1979) found the population to be biased in favor of males. On the contrary, Seigel (1979) found that in a population of Malaclemys terrapin in Brevard County, Florida, females out- number males by as much as 5 to 1. Bull and Vogt (1979) found that in Graptemys, sex is controlled by environ- mental temperature during the middle third of the incubation period. Clutches kept at 25° C in the laboratory produced nearly all male hatchlings, whereas clutches kept at 30.5° produced almost all females. Natural nests that were monitored likewise produced biased sex ratios in hatchlings, depending whether the site was warm and sunny (females predominant) or cool and shaded (males predominant). Regardless of which sex is the larger, SSD relieves intraspecific competition by partitioning food resources. Anoles are typical of reptiles having relatively large males, and for this genus Schoener (1967) and others have amply demonstrated that males, on the average, take larger food items often of different taxa from those taken by females. Also, in anoles the sexes may occupy somewhat differ- ent habitat niches; in species having tree- trunk to ground orientation, males usu- ally perch higher. At the opposite end of the scale, in species with relatively large females, re- productive success is promoted by the fact that reproductive females are re- lieved from competition by immatures as well as by males. In a study of Kansas Thamnophis sirtalis (FMR 123), I found incomplete partitioning of food resources which may be typical of snakes havy- ing SSD in this range. Average weight of females was 155 per cent of male 40 MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY IN_ SAMPLES PERCENTAGES OF TROPICAL SPECIES 80 lOO FMR (% FEMALE TO MALE LENGTH S-V) I20 I40 Fic. 8. Correlation between SSD and climate in squamate reptiles; a trend is evident, with a high percentage of species having relatively large males in tropical climates, and a high percentage hav- ing relatively large females in temperate-zone climates. weight and females took larger food objects, especially mammals. Voles (Mi- crotus ochrogaster) and wood mice (Peromyscus leucopus) were found to be the mainstay of the female diet, but both of these abundant small rodents are beyond the capacity of most males, which prey chiefly upon frogs. On the same area incomplete partitioning of food resources was found in Coluber constrictor (FMR 110). The large fe- males were found to take voles and mice more often than did males, which tended to be more arboreal and had a higher component of insect prey. Graptemys pulchra provides the most extreme case of SSD with the female averaging more than 15 times the male’s bulk, and requiring 3 to 4 times as long to attain sexual maturity. Sexual di- morphism is correlated with food habits, the adult female being specialized for mollusk-eating, with powerful jaws adapted for crushing shells, whereas the male, a more typical emydid in appear- ance, feeds to a large extent on soft- bodied insects (Ernst and Barbour, 1972). Reptiles have not evolved such ex- treme SSD as some other groups of ani- mals. The deep sea ceratioid angler fishes for instance have carried reduction of male size much further; the diminu- tive males attach permanently to the female and derive sustenance from her in a relationship that has been described as sexual parasitism (Bertelsen, 1951). The tiny males of some argiopid spiders which live like commensals in the webs SEXUAL SIZE DIFFERENCES IN REPTILES 4] of their much larger mates, provide ex- on the female, leading to extreme reduc- amples of another type of dependence tion in male size (Gertsch, 1949). 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Smithsonian Contrib. Zool. 300: 20 pp. ZWEIFEL, R. G. 1959. Variation and distribu- tion of lizards of western Mexico related to Cnemidophorus sacki. Bull. Amer. Mus. Nat. Hist. 117(2):63-116. SEXUAL SIZE DIFFERENCES IN REPTILES 53 APPENDIX I Alphabetical list of reptiles, with female-to-male percentages, snout-vent lengths Following each FMR figure, where available, are the male average and (in parentheses) the range and the number in the sample series; the same figures for females follow, and finally the source, abbreviated to the initials of the author(s) with the year of publication. These sources correspond with the publications listed in the Literature Cited in most instances. However, the abbreviation HSF* indi- cates figures from my own unpublished field data or museum specimens examined. The abbreviation var for “various sources” is used in instances where data are based on two or more publications. Ablepharus kitaibelii 115 39.7(33-47) 45.7(35- 51) IEF & SV 61. Ablepharus wahlbergii 110.6 42.0(38-46 in 4) 46.5(44-52 in 4) var. Acanthodactylus cantoris 87 54(39-85 in 17) 47(36-58 in 14) SCA 63. Acanthophis antarcticus 131 440(320-670 in 73) 578(375-825 in 50) RS 80C. Achalinus spinalis 125.4 265.6(217-340 in 5) 332.4(320-368 in 5) var. Agama agama 86.4 (99-123 in 7) (80-112 in 7) var. Agama agilis 87.4 87.3(79-94 in 26) 76.2(64- 89 in 20) SCA 63. Agama atricollis 89.3 153.2(134-171 in _ 5) 137.7(118-153 in 4) var. Agama hispida 95.2 103.3(82-134 in 10) 98.5 (82-118 in 8) var. Agama pallida 109.3. 61.2(55-67 in 20) 67.0 (59-81 in 20) YLW 71. Agama tuberculata 93 121(100-140 in 96) 113 (96-138 in 149) RCW 78. Agkistrodon contortrix 93.5 627.9(501-890 in 116) 586.9(500-678 in 98) HSF*. Agkistrodon halys 112 664.2(480-784 in 9) 743 (697-840 in 4) KK 38. Agkistrodon piscivorus 96 565(450-900 in 96) 493(450-800 in 90) RDB 66. Ahaetulla prasina 121.5 792(710-874 in 5) 962 (773-1075 in 12) FK 41. Alligator mississippiensis 73 3500 2550 (total lengths) RHC & TJ 79. Alopoglossus atriventris 105.9 41-46 43-49 JRD: & PS. 75. Alopoglossus copi 111.1 51.2(44-51 in 5) 57.0 (48-62 in 7) WED ms. Amblyodipsas unicolor 149.5 431(366-495 in 4) 702(410-705 in 4) var. Amblyrhynchus cristatus 85 341 290 JBI 79. Ameiva ameiva 95 114(90-142 in 110) 105 (90-125 in 78) WED ms. Ameiva auberi 82.6 93(78-136 in 23) 77(60- 115 in 23) AS 70. Ameiva festiva 86.1 104.1(94-115 in 16) 89.6 (78-104 in 27) HSF*. Ameiva quadrilineata 96.6 72.5(66-79) 70.0 (62-78) HFH 63. Ameiva undulata 83.8 103.6(93-115 in 43) 86.9(78-106 in 74) HSF*. Amphibolurus maculosus 91 67 61 FJM 73. Amphiesma sauteri 115.5 260(237-282 in 8) 300.5(261-333 in 10) EVM 62. Amphiesma stolata 133 411(400-429 in 11) 587.4(478-654 in 10) FW 11. Amphisbaena alba 103.1 433(305-537 in 34) 447(353-655 in 43) PEV 55. Amphisbaena fuliginosa 97 (251-397) (224-402) inl RD se BS 75; Anniella geronimensis 94 120.2(111-134 in 20) 113.0(111-129 in 18) HSF*. Anniella pulchra 102 129.2(119-142 in 13) 123.0(110-132 in 9) HSF*. Anolis aeneus 71 69.2(67-72 in 10) 49.3(48-52 in 10) TS & AS TIA. Anolis allisoni 74 82.6 in 70 61.0 in 43 TWS 70. Anolis allogus 75.4 56.7 in 202 42.7 in 97 TWS 70. Anolis alutaceus 92.0 35.8 in 55 32.8 in 70 TWS 70. Anolis angusticeps 88 42.0 in 26 37.0 in 37 TWS 70. Anolis aquaticus 88.7 65.9(57-71 in 10) 58.6 (59-62 in 9) HSF 76. Anolis argillaceus 81 44.3 35.8 TWS 70. Anolis attenuatus 95 84.5(78-95 in 24) 80.6 (74-90 in 18) HSF 76. Anolis auratus 104.4 44.6(40-49 in 31) 46.6 (43-49 in 8) HSF 76. Anolis auratus sipaliwinensis 104 43.9(39-48 in 14) 45.9(42-50 in 11) MSH 73. Anolis bimaculatus 71 85.5 60.5 EEW 74. Anolis biporcatus 102 87.0(73-98 in 24) 88.7 (77-97 in 19) HSF 76. Anolis biscutiger 106 37.3(33-43 in 42) 39.4 (36-44 in 33) HSF 76. Anolis bombiceps 110 55-71 65-74 JRD & PSaib: Anolis bourgaei 103.1 54.6(47-61 in 24) 56.3 (46-65 in 13) HSF 76. 54 MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY Anolis bremeri 70 65.3(58-72 in 9) 45.6(39-52 in 9) OHG 72. Anolis brevirostris 89 47.0 in 79 42.0 in 28 TWS 70. Anolis capito 106.4 84.2(78-90 in 13) 89.6 (83-96 in 13) HSF 76. Anolis carolinensis 79 59.9(54-66 in 14) 47.3 (41-53 in 12) HSF 76. Anolis carpenteri 105 38.5(35-41 in 6) 40.4 (35-41 in 14) HSF 76. Anolis chlorocyaneus 76 71.4 in 184 54.0 in 90 TWS 70. Anolis christophei 92 47.6 43.7 TS 70. Anolis chrysolepis 105 71.5(66-79 in 29) 74.4 (67-80 in 32) HSF 76. Anolis coelestinus 78.3 68.6 in 414 53.6 in 174 TWS 70. Anolis concolor 74 68.3(60-80 in 70) 50.5(45-60 in 44) MJC & PLD 73. Anolis cooki 70 59.5 41.6 TWS & AS 71B. Anolis crassulus 88 48.3(39-53 in 8) 42.7(35-56 in 7) HSF 76. Anolis cristatellus 79 63.6 in 327 44.6 in 204 TWS 70. Anolis cupreus 88 47,.4(41-53 in 233) 41.7(37- 48 in 239) HSF 76. Anolis cupreus hoffmanni 97 44.1(38-52 in 314) 42.6(38-51 in 166) HSF 76. Anolis cupreus macrophallus 82 49.6(43-54 in 53) 40.8(34-46 in 33) HSF 76. Anolis cupreus spilomelas 84 49.6(41-55 in 57) 41.7(36-49 in 23) HSF 76. Anolis cuprinus 73 63.3(58-69 in 22) 46.5(42- 53 in 15) HSF 76. Anolis cuvieri 92 41.7 in 22 38.4 in 13 TWS 70. Anolis cybotes 77 65.3 in 230 50.2 in 133 TWS 70. Anolis damulus 110 43.1(37-48 in 9) 47.5(41- 52 in 12): HSE. 76: Anolis distichus 87 50.2 in 450 43.2 in 262 WED & AS 358. Anolis distichus biminiensis 90 46.7(38.3-49.8 in 10) 41.8(36.3-44.2 in 4) JAO 48. Anolis dollfusianus 94 39.0(35-43 in 54) 36.7 (32-40 in 42) HSF 76. Anolis equestris 93 170.9 in 95 158.4 in 66 TWS 70. Anolis evermanni 74 70.7 52.4 TWS & AS 71B. Anolis frenatus 82 132.4(121-143 in 15) 108.9 (100-118 in 20) HSF 76. Anolis fuscoauratus 108 42.0(39-43 in 12) 45.3 (40-50 in 12) HSF 76. Anolis fuscoauratus kugleri 102 44.5(40-49 in 9) 45.3(41-48 in 10) MSH 73. Anolis gadovii 89 70.6(62-76 in 10) 62.6(56-69 in 12) HSF 76. Anolis garmani 75 110 82.5 TWS 70. Anolis gemmosus 94 62.5(58-66 in 38) 58.5 (56-63 in 28) HSF 76. Anolis grahami 68 65.5 44.0 TWS & AS 71A. Anolis grahami aquarum 73 61.8 45.1 TWS & AS 71A. Anolis gundlachi 69 64.8 45.2 TWS & AS 71B. Anolis hendersoni 84 47.9 in 165 40.2 in 86 TWS 70. Anolis heteropholidotus 109 48.6(45-51 in 10) 53.1(49-58 in 7) HSF 76. Anolis homolechis 78 52.3 in 355 40.7 in 107 TWS 70. Anolis humilis 105 36.7(32-43 in 155) 38.5 (34-43 in 106) HSF 76. Anolis intermedius 99 46.0(39-54 in 241) 45.5 (39-53 in 98) HSF 76. Anolis isthmicus 89 54.4(50-63 in 25) 48.4 (44-58 in 9) HSF*®. Anolis kemptoni 104 48.0(45-53 in 13) 50.1 (46-54 in 21) HSF 76. Anolis krugi 79.4 49.7 39.3 TWS & AS 7I1B. Anolis lemurinus 104 67.0(59-79 in 13) 69.6 (59-78 in 16) HSF 76. Anolis limifrons (Costa Rica) 103 37.5(33-43 in 392) 38.6(34-45 in 276) HSF 76. Anolis limifrons (Panama) 99 43.9(38-48 in 8) 43.25(41-46 in 8) HSF 76. Anolis lineatopus 69 60(50-70) 42(37-47) TAJ 15; Anolis lionotus 84.8 71.5(65-78 in 19) 60.6 (56-68 in 24) HSF 76. Anolis loysiana 89 40.4 in 18 36.0 in 7 EWS