Digitized by the Internet Archive in 2012 with funding from Royal Ontario Museum http://archive.org/details/thermalrelationsOOvald *to 'Sniq ^ ^ 0.05. Specimens collected were deposited in the Royal Ontario Museum, Toronto, and identi- fications were made by the authors. Species Studied — Hyla labialis, a semi-arbo- real frog, occurs in moist situations in the highlands (2,000-3,500 m) of the eastern Andean Cordillera of Colombia from the southern part of the Departamento de Cun- dinamarca northward into the Departamento de Norte de Santander (Cochran and Goin, 1970). This species, although strongly helio- tropic, is active during day and night. Frogs frequently rest in the open and bask on vegetation near pools of still water in gar- dens, grassy margins of spring basins, in flat pastures of dense, matted grasses and sedges, and on plants in paramos (Stebbins and Hendrickson, 1959). Reproduction is acy- clic, and oogenesis occurs throughout the year (Hunter and M. de Valdivieso, 1962). The call, a low croak, is given occasionally during the day but is more commonly heard during the early hours of darkness. H. labialis has several colour phases (Dunn, 1944), but the most frequent colouration is a uniform, bright green dorsum, with a paler venter and blue in areas of concealed sur- faces. Some frogs lack any shade of green and are golden brown. Between these ex- tremes occur all combinations of dorsal colouration, with various shades of green or golden brown forming irregular spots on the background. This frog has some ability to change the tone of colour but not the pat- tern. Adult males, distinguished by a vocal sac and the swollen base of the thumb, reach 43 mm in SVL whereas larger adult females may measure 60 mm. Most frogs studied (150) were juveniles that measured 20-34 mm in SVL. Twenty-eight were adult males (SVL 35-39 mm), and nine were adult females (SVL 42-60 mm). Nine frogs with SVLs between 39 and 42 mm were classi- fled as young adult females (ova 60 mm) fell in February, April through June, and September through No- vember, and in 1969 in April through June and October through December. In July 1967 precipitation measured 84.6 mm and was recorded on 21 days; in June and July 1969 precipitation was 69.2 mm for 17 days in June and 14.1 mm for 14 days in July. Normal, daily temperature fluctuation is from 4.4°C at night to 17.2°C in midafter- noon (U.S. Army, 1961). The yearly mean temperature at Bogota is 14.5°C and nearly constant from warmest to coldest months (Perez Arbelaez, 1954). In July 1967 and in June and July 1969 the minimum re- corded air temperatures, respectively, were 3.5°, 6.2°, and 0.9°C, and maximum tem- peratures were 19.6°, 22.2°, and 20.8°C, respectively. The annual mean relative hu- midity at Bogota is 69 per cent (Perez Arbelaez, 1954), and mean relative humidi- ties for July 1967 and June and July 1969 were 73, 78, and 79 per cent, respectively. For these months relative humidities were higher in the morning (46-100 per cent) and in the evening (60-94 per cent) and lower in the early afternoon (41-79 per cent). Mean and extreme dew point values for July 1967 and June and July 1969 were, respectively, 7.9 (7.0-8.7), 11.1 (9.3- 12.1), and 11.7 (10.6-12.8). Winds were never strong, and mean velocities (m/sec) averaged 6.1 in July 1967 and 5.2 and 6.9, respectively, in June and July 1969. The total annual variation in day length at lati- tude 4°N in Colombia is approximately 24 minutes (Miller, 1959). Results Body Temperatures — The activity range of H. labialis was 11-28°C (Table 1). The minimum (11.4°C) was recorded from an adult female exposed on vegetation at night (1935 hr) when Ta = Tb. The maximum (28.0°C) was that of an adult, basking male at 1406 hr when Ta was 16.0°C. The mean T, of all frogs was 18.2°C ± 0.29. Activity ranges of age groups were 11.8-27.6°C for juveniles, 16.2-26.4°C for young adults, and 11.4-28.0°C for adults. The basking range of all frogs was 18.0-28.0°C (al- though only one Tb was 28.0°C, and most were less than 25.0°C). Tbs among age groups, however, did not differ from each other (F-ratio = 0.731 ns; df = 2, 193). T,,s of frogs taken in the morning (mean, 19.8°C ± 0.51) were not statistically dif- ferent (F-ratio = 1.851 ns; df = 1, 130) from those taken in the afternoon (mean, Table 1. Ambient (T.) and body (T„) temperatures (°C) of the frog Hyla lubialis from Bogota, Colombia Activity n Mean ± S.E. range CV DAY Basking T„ 26 22.9 ± 0.58 18.0-28.0 12.8 Ta 17.2 ± 0.43 13.4-20.8 12.8 Shade, exposed on plants r„ 68 20.5 ± 0.43 15.4-27.6 17.3 T. 15.2 ± 0.20 12.2-19.8 11.0 Shade, concealed in plants T„ 37 16.9 ± 0.24 14.6-21.2 8.7 Ta 15.6 ± 0.20 13.6-18.8 8.0 All frogs Tb 131 20.0 ± 0.32 14.6-28.0 18.3 T. 15.7 ± 0.16 12.2-20.8 11.8 NIGHT Exposed or plants T„ 47 14.2 ± 0.24 11.4-19.0 11.6 Ta 11.6 ± 0.14 9.6-13.4 8.5 Concealed in plants Tb 18 15.5 ± 0.51 12.4-20.8 14.1 Ta 13.3 ± 0.25 10.8-15.0 7.8 All frogs Tb 65 14.5 ± 0.24 11.4-20.8 13.1 Ta 20.1 ± 0.15 9.6-15.0 10.3 19.5°C ± 0.43). The lowest Tb taken in the morning was 14.8°C (Ta = 15.4°C) at 1140 hr from an adult male concealed in vegetation on a cloudy morning, and the highest morning Tb (27.6°C) was recorded from a basking juvenile at 1112 hr when Ta = 15.2°C. The lowest afternoon T„ (14.6°C) was that of an adult female con- cealed in vegetation at 1515 hr when the sky was overcast and Ta was 14.2°C. Tbs of frogs taken in the morning and afternoon were significantly higher (f-ratio = 124.537***; df = 1, 194) than those taken at night. At night the highest T,, (20.8°C) was that of a juvenile concealed in vegeta- tion (1612 hr; T„ = 16.0°). The mean Tt, for frogs taken at night was 14.7°C ± 0.25. Response to Environmental Temperatures — SVLs of all frogs on body and air tempera- tures were tested by the least-squares method of regression. SVLs and Tbs were not statis- tically related (t = 0.669 ns; df = 172), nor were SVLs and Tas (t = 0.034 ns; df = 174). Body temperatures generally exceeded air temperatures (Fig. 1 ) , and a line was fitted to these data by the method of Bartlett. The regression of Tbs and Tas was statisti- cally significant (T0 = 12.848***; df = 193), but there was no statistically signifi- cant departure from isometry (Tx = 0.134 ns; df = 193) or from linearity (TL = 0.388 ns; df = 193). Moreover, all correlations of Tas and Tbs were statistically significant (all temperatures: r = 0.674***, df = 194; diurnal temperatures: r = 0.437***, df = 129; nocturnal temperatures: r = 0.311**, df = 63). Although the regression and cor- relations are significant, this merely indicates a causal relationship between T„s and Tbs, but the closeness of such a relationship may not be biologically important and could be due to a common relation to other variables such as metabolic, bioclimatic, and even geographic conditions. Only 30 frogs possessed Tbs within 1°C of the air temperature. Nine individuals were recorded with Tbs 0.2°-1.2°C less than ambient temperatures, and six frogs main- tained T,,s greater than 10°C above ambient O o o A 28 - o A Day (sun) Day (shade) o A 26 • Night O A o AA A ATAOA o A A o o o / 24 A AO A A A A AT o ° A / /o 22 A A O A o / °0 A A O o / / / A A / / / 20 3 - •A A0 A° V A AT / OA ATA / A . TO / A A / / / / / / / t 18 A •A A / / A ./A A A / A A A /A A i* / / / AOO / ±rAy A A / .. A V AT / A AA AT A AT A i/ * AT AT / LW AT A / 16 • ••# A- A • « * •* T ATA A/ «T A / AT / A / A 14 >•••••• A •> •!• A A / / / • / _ / • •• ## •• A • t 12 7 I I V I I ! , I I 1 1 1 1 10 12 14 16 18 20 22 Fig. 1 — Model n regression of body temperatures (T„) on ambient temperatures (Ta). The dashed line connects isothermal points. The solid line is the regression line (Y = 0.99+ 1.27X). temperatures. Only five frogs had Tbs that were isothermic with ambient temperatures. Body temperatures of frogs in deep shade deviated the least (1.6°C ± 0.23) from ambient temperatures, and those with the greatest deviations of Tbs from Tas were basking frogs (5.8°C ± 0.68) and frogs in exposed, resting positions under overcast skies (5.3°C ± 0.35). The maximum posi- tive deviation of Tb from Ta (12.0°C) was that of one basking frog. Coefficients of variation (CV) of Ths of frogs in different environmental situations ranged from 8.7 to 17.3 (Table 1). The least variable Tbs were those of frogs con- cealed in vegetation on cloudy days, those of frogs exposed on vegetation at night, and those of frogs that were basking. The largest CVs were those of temperatures of frogs concealed in vegetation at night and of those exposed on vegetation in the day during cloudy periods. Tas, however, were generally less variable than Tbs (Table 1), and the lowest CVs were those of T.,s taken at night and in vegetation on cloudy days. Heterogeneity among Tbs of frog samples was pronounced (F-ratio = 17.792***; df = 4, 191), more so during the day than at night (Fig. 1). Results of Duncan's multiple range test (Table 2) demonstrated that of the five means tested, only two subsets were significantly different, and the non-significant subsets were sharply demarked into those frogs with higher Tbs and those with lower Tbs. Daily Activity Cycle — Adults and subadults of Hyla labialis were active in the morning and early afternoon but were seldom out at night. Juveniles, on the other hand, were active at all hours but most active at night. At Tas of 16°C or greater and Tbs more than 18-20°C, frogs began to jump and were difficult to approach. If T.,s were less than 16°C and Tbs less than 18-20°C, frogs did not jump but walked slowly when dis- turbed. Lethargy induced by cold did not immobilize them, however, as frogs could easily be prodded to move when Tbs were as low as 12°C. Although calls were heard occasionally during the day, most frogs be- gan to call at dusk and then intermittently throughout the night. Daily cycle of activity was influenced by fluctuating meteorological conditions. Heavy rain (8.5 mm) inhibited activity, but light continuous rain (0.5 mm) increased activity. Usually a continuous drizzle throughout the night and dew in the early morning also in- creased activity. Frogs tended to remain concealed in vegetation during days with periods of light cloudiness and occasional sprinkles. Winds were usually light in the early morning (ca 0.96 m/sec at 0700 hr) and early evening (ca 2.12 m/sec at 1900 hr) but stronger toward mid-day (ca 5.23 m/sec at 1 300 hr) and did not seem to affect Table 2. Results from Duncan's multiple range test for body temperatures (CC) of the frog Hyla labialis from Bogota, Colombia. Horizontal lines connect maximally non-significant subsets of means. Basking Other positions Exposed (shade) on plants Concealed (day) in plants Concealed (night ) in plants Exposed (night) on plants Mean ± S.E. n 22.9 ± 0.58 26 20.5 ± 0.43 68 16.9 ± 0.24 37 15.5 ± 0.51 18 14.5 ± 0.24 47 noticeably activities of frogs. Maximum wind velocities, e.g., 10.3 m/sec on 4 days in July 1969, similarly did not affect be- haviour. H. labialis did not orient themselves to receive maximal, incident insolation but maintained a fixed position for several hours when basking. Positions appeared to be ran- dom or disoriented to the direction of the sun. The shape of the plant or object on which they rested appeared to determine their orientation. Moreover, they usually did not move if shade or partial shade resulted from a change in the position of the sun. They normally rested on leaves of plants in a semihorizontal, prostrate position with the posterior part of the body toward the petiole. They were rarely seen in vertical positions or on broad-leaved plants. Once a resting or basking site was occupied, a frog rarely moved from it during the day. The diurnal site was usually abandoned at dusk or after sunset. Often a frog would bask or rest at the same site for several consecutive days, e.g., an adult female basked in the centre of a rose flower for 4 consecutive days in July 1969. Casual observations indicated that frogs of both colour phases basked equally on plants with green or dark-red leaves, but when exposed at night, more appeared to occupy leaves of dark-red plants rather than those of green plants, possibly to minimize heat loss. Discussion — In thermoregulatory behaviour, H. labialis is a thermophilic heliotherm whose body temperatures are usually higher than ambient temperatures owing to basking or by absorbing solar radiation that filters through light cloud cover. Although the activity range of body temperatures of H. labialis was previously reported to be only a few degrees (Brattstrom, 1970), we found this frog to have an activity range of almost 17°C. Although data are meagre for high-alti- tude, neotropical anura, Tbs of H. labialis are not unlike other eurythermic, montane species of the genus; e.g., H. regilla from Oregon has an activity range of 8-22 °C but a lower mean T,, (15°C as opposed to 18.2°C in H. labialis), and H. calijorniae has an activity range of 13-26°C and a mean T,, of 19.5°C (Brattstrom, 1963). Data presented here for H. labialis support the conclusion of Brattstrom (1968) that neotropical, montane frogs, in terms of ability to adjust physiologically to tempera- ture changes, react similarly to temperate species from equivalent thermal latitudes. Moreover, H. labialis, which has a relatively narrow altitudinal distribution and a wide geographic distribution, differs from many lowland-derived montane hylids with re- stricted geographic ranges (Brattstrom, 1970) by having a wide temperature toler- ance but little ability for short-term physio- logical adjustment (Hutchison, 1971). In the Andes, ambient temperatures are modified by long-distance ocean effects, whereas insolation, on the other hand, is correlated with latitude (Schwabe, 1968). The discordance between insolation and ambient temperatures results in pronounced, daily climatic fluctuations, and at high alti- tudes differences between microclimates are exaggerated. Consequently, a wide selection of temperatures is encountered. In air, amphibians may have temperatures well above ambient when exposed to radiant heat, but, in shade, their body temperatures tend to fall toward the dew point, as the skin presents a moist surface (Lillywhitc, 1971 ). Dew point fluctuates less than dry bulb tem- peratures, and terrestrial amphibia therefore have a more constant thermal environment than would be otherwise expected (Fry, 1967). In the Bogota Savanna, frost, except at ground level, is rare, although night-time temperatures lower than 10°C (e.g., 8.2°C on 15 July 1967) are not uncommon. That low temperatures per se are ever a serious problem is unlikely for H. labialis, which spends considerable time in sheltered loca- tions. Moreover, these frogs apparently do not exhibit heat stress, for they were never seen to retreat from exposure to continuous sunlight to microhabitats that had lower ambient temperatures. Resumen — Estudiamos las relaciones ter- males de la rana heliotermica Hyla labialis en Bogota, Colombia, a una altura de 2.650 m en julio de 1967 y en junio y julio de 1969. Los modelos de actividad diarios son controlados principalmente por la tempera- tura. Cielos nublados, lo mismo que tem- peraturas bajas, reducen los movimientos de este anfibio. H. labialis mantiene tempera- turas corporales entre limites bastante amplios. Dichas temperaturas son afectadas notablemente por las temperaturas ambien- tales. Limites de actividad normal de las temperaturas del cuerpo varian de 11°C a 28°C, siendo la temperatura media 18.2°C. Las temperaturas corporales de la mayoria de las ranas estudiadas (76 por ciento), sin embargo, se extienden entre 13°C y 22°C. El promedio de las temperaturas del cuerpo es inferior durante la noche (14.5°C) y superior cuando se exponen al sol (22.9°C). El comportamiento termorregulatorio de esta rana se debe a la insolation o a la absorcion de radiation solar que penetra a traves de ligeras capas de nubes uniformes. Por esta razon las temperaturas del cuerpo son usualmente mayores que las tempera- turas ambientales. H. labialis permanece considerable tiempo en lugares resguardados, aparentamente no exhiben tension termal alguna debido a los rayos solares, ya que estas ranas no se retiran de sus moradas de exposition continua al sol a otros lugares de temperaturas ambientales inferiores. Acknowledgments — We thank Dr. J.M. Idrobo, Instituto de Ciencias Naturales, Bo- gota, for identification of plants; Dr. Gabriel Echeverry Ossa, Servicio Colombiano de Me- teorologia e Hidrologia, Bogota, for climatic data; and Dr. Dennis M. Power, Santa Bar- bara Museum of Natural History, California, Dr. P.D. Vanzolini, Museu de Zoologia, Sao Paulo, and Dr. Alan J. Baker, Department of Ornithology, rom, for advice concerning statistical procedures. We are grateful to Dr. Alan J. Baker for critically reading the manuscript and to Ms. E. Dowie, ROM Library, for assistance with literature cita- tions. Special thanks are due Dr. Victor H. Hutchison, University of Oklahoma, for ad- vice and encouragement during the early stages of the project. The assistance and co- operation of the staff of the Department of Mammalogy, ROM, is gratefully acknowl- edged. The graph was prepared by Mrs. Sophie Poray, ROM. This research was sup- ported by a Sigma Xi-RESA Grant-in-Aid of Research to the senior author. Literature Cited BARTLETT, M.S. 1949 Fitting a straight line when both variables are subject to error. Biometrics, 5 (3): 207-212. BRATTSTROM, B.H. 1963 A preliminary review of the thermal requirements of amphibians. Ecology, 44 (2): 238-255. 1965 Body temperatures of reptiles, Am. Midi. Nat., 73 (2): 376-422. 1968 Thermal acclimation in anuran amphibians as a function of latitude and altitude. Comp. Biochem. Physiol., 24 (1): 93-111. 1970 Amphibia. In Whittow, G.C., ed. Comparative physiology of thermoregulation. Vol. 1 . Invertebrates and nonmammalian vertebrates. New York, Academic Press, pp. 135-166. cochran, d.m. and C.J. GOIN 1970 Frogs of Colombia. Bull. U.S. Natn. Mus., 288: 1-655. cowles, r.b. and cm. bogert 1944 A preliminary study of the thermal requirements of desert reptiles. Bull. Am. Mus. Nat. Hist, 83 (5): 261-296. DAVIES, R.G. 1971 Computer programming in quantitative biology. London, Academic Press. 492 pp. DUNCAN, D.B. 1955 Multiple range and multiple F tests. Biometrics, 11 (1): 1-42. DUNN, E.R. 1944 Herpetology of the Bogota area. Revta. Acad. Colomb. Cienc. Exact. Fis. Nat., 6: 68-81. ESPINAL T., L.S. and E. MONTENEGRO M. 1963 Formaciones vegetales de Colombia. Bogota, Instituto Geografico de Colombia "Augustin Codazzi." 201 pp. FRY, F.E.J. 1967 Responses of vertebrate poikilotherms to temperature. In Rose, A.H., ed. Thermo- biology. London, Academic Press, pp. 375-409. HUNTER, A.S. and B. MURCIA DE VALDIVIESO 1962 La reproduction de la rana, Hyla labialis. Caldasia, 8 (40): 573-583. HUTCHISON, V.H. 1971 Herpetological expedition to Colombia. In Dehser, P.H., ed. National Geographi- cal Society research reports . . . during the year 1965. Washington, D.C., National Geographical Society, pp. 113-122. KRAMER, C.Y. 1956 Extension of multiple range tests to group means with unequal numbers of replica- tions. Biometrics, 12 (3): 307-310. LILLYWHITE,H.B. 1971 Thermal modulation of cutaneous mucus discharge as a determinant of evaporative water loss in the frog. Rana catesbeiana. Z. Vergl. Physiol., 73 ( 1 ) : 84-104. MILLER, A.H. 1959 Reproductive cycles in an equatorial sparrow. Proc. Natn. Acad. Sci., 45 (7): 1095-1100. PEREZ ARBELAEZ, E. 1954 Los recursos naturales de clima en Colombia. Capitulo 3. In Perez Arbelaez, E. Recursos naturales de Colombia. Segunda Entrega. Bogota, Instituto Geografico de Colombia "Augustin Codazzi," pp. 129-207. SCHWABE, G.H. 1968 Toward an ecological characterisation of the South American continent. In Fittaku, E.J. et «/., eds. Biogeography and ecology in South America. Vol. 1. The Hague, Dr. W. Junk N.V., pp. 113-126. sokal, r.r. and F.J. rohlf 1969 Biometry; the principles and practice of statistics in biological research. San Fran- cisco, W.H. Freeman. 776 pp. stebbins, r.c. and J.R. hendrickson 1969 Field studies of amphibians in Colombia, South America. Univ. Calif. Publ. Zool., 56 (5): 497-540. U.S. ARMY 1961 Army area handbook for Colombia. Washington, D.C., U.S. Government Printing Office. 595 pp. VANZOLINI, P.E. 1969 Comment on multiple comparisons of samples with unequal numbers. Copeia, 1969 (4): 866. 10 Suggested citation: Life Sci. Occ. Pap., R. Ont. Mus. All manuscripts considered for publication are subject to the scrutiny and editorial policies of the Life Sciences Editorial Board and to review by persons other than Museum staff who are authorities in the particular field involved. Price: 60