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Full text of "International journal of comparative psychology"

ISSN 0889-3667 
IJCPB 7(1)1-43(1994) 




IISICIP 




INTERNATIONAL JOURNAL OF 

COMPARATIVE 
PSYCHOLOGY 

Published by 

The International Society 

for 

Comparative Psychology 



VOLUME?, NUMBER 1 



EDITOR 

Robert N. Hughes 

Dept. of Psychology 

University of Canterbury, PB 4800 

Christchurch, New Zealand 



ASSOCIATE EDITOR 

Nancy K. Innis 
Dept. of Psychology 
University of Western Ontario 
London, Ontario, N6A 5C2 Canada 



MANAGING EDITOR 

Sally A. McFadden 

Dept. of Psychology 

The University of Newcastle 

Newcastle, NSW 2308 Australia 



EDITORIAL ADVISORY BOARD 



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L.C. Simbayi 

Dept. of Psychology 

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Jiao Shao 

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Peking University 
Beijing 100871 China 



INTERNATIONAL JOURNAL 
OF COMPARATIVE PSYCHOLOGY 



Volume 7, Number 1, 1994 



ARTICLES 

Flavour-Meal Size Conditioning in the Rat (Rattus norvegicus): 

Failure to Confirm Some Earlier Findings 1 

Leickness Chisamu Simbayi 

Light Mediation of Circadian Predatory Behavior in the 

Young Alligator 27 

Jack A. Palmer and Linda K. Palmer 

Portia labiata, a Cannibalistic Jumping Spider, 

Discriminates Between Own and Foreign Eggsacs 38 

Robert J. Clark and Robert R. Jackson 



INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY is sponsored 
by the International Society for Comparative Psychology, an affiliate of the International 
Union of Psychological Sciences. In consonance with the goals and activities of the 
Society, it publishes reports of studies in the evolution and development of behavior of 
all species; on the use of the comparative method for the understanding of behavioral 
processes; and the examination of the adequacy of psychological and evolutionary 
theories. It accepts articles that deal with historical and contemporary relationships 
between humans and other animals; that elucidate problems of ecological and behavioral 
processes in resource management; that explicate fundamental concepts about human 
evolution; and that present research results and develop theories about the development 
and evolution of behavior. Articles on the contemporary and historical organization of 
knowledge about comparative psychology; promoting public education on the evolution 
and development of behavior; and about the training of students in comparative 
psychology are also invited. Book reviews; letters discussing published articles with 
replies by authors; notices of new books, journals, meetings and competitions or other 
matters of interest to the readers will be published at the discretion of the editors. The 
Editor, Associate Editor and Managing Editor are elected by the Operations Committee 
of the Society. The Editorial Advisory Board is appointed by the Editors and the 
Operations Committee. 

MANUSCRIPTS should be submitted in triplicate to Robert Hughes, Editor. See inside 
back cover for style requirements. 

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McFadden@psychology.newcastle.edu.au or Fax 61 49 216980). 

Subscription rates: 

Volume 7, 1994 (4 issues) $95.00 (outside the U.S., $110.00). Members of the 
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part of their membership dues. For membership information see back pages. 

INDEXED OR ABSTRACTED IN: Psychological Abstracts. 

PHOTOCOPYING: Authorizations to photocopy items for internal and personal use 
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COPYRIGHT 1994 by the International Society for Comparative Psychology. 
Published quarterly. 



ISSN 0889-3667 IJCPE8 7( 1 ) 1 -43( 1 994) 



International Journal of Comparative Psychology, Vol. 7, No. 1, 1994 



FLAVOUR-MEAL SIZE CONDITIONING IN THE 

RAT (RATTUS NORVEGICUS): FAILURE TO 

CONFIRM SOME EARLIER FINDINGS 

Leickness Chisamu Simbayi 
University of Port Elizabeth 



ABSTRACT: A series of experiments was carried out in order to explore further the 
possibility that hungry rats, both mature and weanling, might learn to associate flavours 
with different sizes of meals made from the same diet. The general procedure used 
involved providing rats with either a large meal (e.g. 5 gm). usually consisting of wet 
mash with an added flavour such as anise, or a small meal (e.g. 1 gm) of the same diet 
with a second flavour such as vanilla added, on alternate days. Following a number of 
such discrimination training days, subjects were given a two-jar extinction choice test 
to assess their relative preferences for the two flavours. It was originally anticipated that 
rats would come to prefer the flavour associated with the larger meal (i.e., conditioned 
appetite), because the larger meal provided more calories. However, this result was 
never obtained. When a significant preference was acquired, this was for the flavour of 
the small meal instead, (i.e. conditioned satiety). The conditioned effects not only 
extinguished very rapidly but were also rather elusive at times. It is thought that the 
observed conditioned satiety effects were probably due to flavour-calorie rather than 
flavour-flavour associations. 

A central theme in a number of current theories of food intake 
control is the idea that omnivores such as rats or human beings regulate 
their food intake on a short-term basis, that is, within a meal, by 
associating the caloric consequences of ingestion with the flavour of 
foods (e.g., Booth, 1985; Deutsch, 1987; Le Magnen, 1987). This 
phenomenon which is known as conditioned satiety is considered to be 
very important because it means that the omnivores do not necessarily 
have to wait until they have actually experienced the delayed results of 
digestion, namely, calories, before they terminate feeding. They can 
instead simply rely on their previous experience with familiar flavours 



Address correspondence to Leickness Simbayi. Psychology Department, University 
of Port Elizabeth, P.O. Box 1600, Port Elizabeth 6000, South Africa. 

© 1994 International Society for Comparative Psychology 1 



2 INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY 

as cues for satiety. Accordingly, inability to make such associations may 
be responsible for inducing some pressing human problems such as 
obesity (Booth & Mather, 1978), alcoholism (Deems, Getting, Sherman 
& Garcia, 1986) and drug withdrawal problems (Le Magnen, 
Marfaing-Jallat & Miceli, 1980). 

A complementary process known as conditioned appetite which also 
involves learning about flavour-food relationships has been implicated 
as a food selection mechanism on a more long term basis whereby 
omnivores choose their food after learning about the caloric values of 
different foods (Bolles, 1983; Bolles, Hay ward & Crandall, 1981; 
Hay ward, 1983; Mehiel & Bolles, 1984; Rozin, 1977). It is thought that 
rats are perhaps adept at learning about both of these types of 
conditioned preferences in much the same way as they acquire 
conditioned taste aversion (CTA) learning or bait shyness. In contrast 
to the very considerable and unequivocal evidence for CTA learning in 
rats which has been accumulated over the past three decades or so of 
research (see Riley & Tuck, 1985), evidence for positive conditioned 
flavour preferences, which include both conditioned satiety and 
conditioned appetite, is relatively less strong and unconvincing. This 
seems rather surprising in view of the fact that the idea of the 
involvement of such learning mechanisms in the regulation of feeding 
behaviour was originally proposed as early as 1955 by Le Magnen (see 
Le Magnen, 1969). 

Although there is mounting evidence in support of the idea that rats 
are capable of learning about positive flavour preferences (e.g., Boakes 
& Lubart, 1988; Boakes, Rossi- Amaud & Garcia-Hoz, 1987; Capaldi, 
Campbell, Sheffer & Bradford, 1987; Simbayi, 1987; Simbayi, Boakes 
& Burton, 1986) most of the evidence demonstrated conditioned appetite 
rather than conditioned satiety. It is interesting to note here that most 
of these studies had employed fluids such as glucose, saccharin and 
ethanol rather than solid food as reinforcers. In contrast, a relatively 
small number of studies have also demonstrated conditioned flavour 
preferences using solid food in other animals such as humans (e.g., 
Booth, Lee & McAleavey, 1976; Booth, Mather & Fuller, 1982) and 
chicks (e.g., see Capretta, 1961; Hogan, 1977, 1980). These studies 
could be considered more informative about conditioned preferences than 
those that used fluids as reinforcers, because most of the food of 
omnivores is in solid rather than liquid form. 

The fact that the experimental demonstration of conditioned satiety 
has proved to be rather elusive has been hitherto acknowledged by Smith 
and Gibbs (1979). According to them, only two studies, one by Booth 
(1972) and the other by Booth and Davis (1973), had successfully 



LEICKNESS C. SIMBAYI 3 

demonstrated conditioned satiety learning in rats. In his initial study, 
Booth (1972) found evidence for the ability of flavours to elicit 
conditioned satiety in rats. In this research, flavours were paired with 
high or low calorie diets during training and presented to the rats one at 
a time. During testing, when the two flavours were presented one at a 
time in isocaloric diets, the "low calorie" flavour was preferred more 
than the "high calorie" flavour. However, in a two stimulus preference 
test in which the flavours were presented simultaneously in isocaloric 
diets, the high-calorie flavour was preferred more than the low calorie 
flavour. This latter result demonstrated conditioned appetite. Similar 
findings have also been reported by Booth and Davis (1973). However, 
similar studies carried out by Bolles et al. (1981) and Hay ward (1983) 
were only able to demonstrate conditioned appetite but not conditioned 
satiety. Perhaps even more interesting was Hayward's findings which 
also showed that young rats were capable of more diverse learning than 
adult rats. 

The experiments reported in the present paper were undertaken in an 
attempt to explore further the positive conditioned flavour preference 
effects reported by Booth (1972), Bolles et al. (1981) and Hay ward 
(1983) using wet solid food as a reinforcer. To test the validity of 
Haywood's (1983) developmental finding, conditioned flavour 
preferences were investigated in adult rats in Experiments 1, 2 and 4, 
and in rat pups in Experiment 3. 



EXPERIMENT 1 

This experiment was a partial replication of experiments carried out 
by Bolles et al. (1981), except for the following changes: 

a) The ratio of meal sizes was increased to 5:1 instead of 2:1. It was 
hoped that the ratio increment would serve to make the meal sizes 
more easily discriminable. 

b) To prevent rats from learning to anticipate or predict specific 
flavours during each subsequent training day, semi random 
presentations of flavour-meal size correlations replaced the 
alternating presentations every other day adopted by Bolles et al 
(1981). 

c) Control groups were added for which supplementary food (wet mash 
of standard laboratory chow) was made available 15 min after the 



4 INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY 

presentation of small meals. These control groups were somewhat 
similar to the Oral Group used in Bolles et al.'s (1981) Experiment 
4 and were meant to equate the total caloric consequences of both 
meal sizes and thereby controlling for any possible confounding 
effects of differential hunger. 

Basically, rats were given experience with two meal sizes of the 
same diet, each of which was marked by a distinctive flavour (anise oil 
or vanilla). Thus, the two distinctive flavours were correlated with the 
same pattern of oral cues and caloric density but different caloric 
consequences: that is, large meals yielded more calories than smaller 
ones. The conditioning of flavour preferences was assessed by the 
degree to which the animals tracked the flavours in an extinction choice 
test when they were no longer correlated with meal size. 



METHOD 

Animals 

Twenty male hooded Lister rats were obtained from Sussex University's 
Laboratory of Experimental psychology breeding colony. They had been 
used previously in a food neophobia experiment but had no experience 
with either the reinforcer or flavours used in the present experiment. 
The rats were fed for only 2 h each day beginning at 1500 hrs and were 
food deprived for the rest of the day except for 30 - 60 mins beginning 
at 1000 hrs each morning when training or testing was conducted. More 
importantly, the animals also had some previous experience with feeding 
from jars and their mean consumption time for 5 gm of wet unflavoured 
mash was about 5 min. The average age and weight of the rats at the 
beginning of the experiment were 100 days and 250 gm respectively. 

Materials 

The experimental flavours, which were added to the chow diets, 
were made by adding 0.5 ml anise oil (Sigma London Chemical 
Company Limited, Poole, Dorset, England) and 2.0 ml vanilla (E.F. 
Langdale Ltd., New Addington, Surrey, England) extracts to 100 ml 
water. These flavour concentrations were chosen following a titration 
experiment which tested for sensitivity of rats to flavours relying on food 
neophobia as the dependent variable. Both the conditioning and testing 
diets consisted entirely of standard laboratory chow (Spratt's Expanded 



LEICKNESS C. SIMBAYI 5 

Rodent Diet, Spiller's Limited, Newmarket, Suffolk, England) to which 
some water was added and yielded about 2 cal/gm. 

All conditioning and testing was carried out in the animals' home 
cages where both the conditioning and testing diets were presented in 
feeding jars with holes in the lids large enough for the rats to insert their 
heads in order to reach the food. During testing the jars were attached 
in pairs to prevent rats from altering the position of each jar relative to 
the other. In addition, the pairing arrangement also made it possible to 
effectively counterbalance for any positional biases. 

Experimental design 

A 2 X 2 factorial design was used with large meal flavours (anise vs. 
vanilla) and supplementation (whether or not the animal had received 
supplementary food on small meal days during conditioning) as factors. 
The experiment had two major phases during which conditions were 
reversed. For each subject the treatments in each phase were identical 
except that the relation between flavour and meal size was reversed. 
Each phase consisted of two 8-day conditioning cycles, each of which 
were followed by a single test day. Finally, a 5-day interval separated 
the two phases during which no flavours were presented and the same 
food deprivation schedule as used in the actual experiment was also 
maintained. 

Procedure 

Conditioning involved presenting flavour-meal size correlations for 
blocks of 8 days in semi random order, that is, a total of 4 days with 
each flavour. The animals were randomly assigned to four equal groups 
(n = 5) namely. Groups V, VS, A and AS. Groups V and VS were 
presented with a large meal (5 gm) flavoured with 2.0 % vanilla on 
some days and a small meal (1 gm) flavoured with 0.5 % anise oil on 
other days. On the other hand. Groups A and AS were both presented 
with a large meal (5 gm) flavoured with 0.5 % anise oil on some days 
and a small meal (1 gm) flavoured with 2.0 % vanilla on the other days. 
However, in addition, Groups VS and AS also received a supplement of 
4 gm of unflavoured plain chow (also in wet mash form) 15 min after 
consuming the small meals. On any given conditioning day, all the 
animals received the same flavour: for example, on a typical 'vanilla 
day', Group V and VS received large vanilla flavoured meals, while 
Groups A and AS received small vanilla flavoured meals, and only 
Group AS received the 4 gm of supplementary food after 15 min. The 



6 INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY 

flavoured meals used for conditioning were presented at 1 000 hr while 
maintenance food was presented for 2 h beginning at 1500 hr. 

Testing was done using a two jar extinction choice paradigm which 
involved comparing the consumption of two diets presented 
simultaneously in equal amounts in two feeding jars. Each jar contained 
20 gm of either anise or vanilla flavoured food in wet mash form. 
Testing lasted for only 10 min beginning at 1000 hr on each test day. 
The positions of test foods were counterbalanced for each pair of 
animals to minimise any positional biases. The first test was done on 
Day 9 (Phase 1) after which the conditioning cycle was repeated for 
another 8 days. Then, another choice test followed on Day 23 (Phase 2). 

In order to further demonstrate the consistency and resilience of the 
phenomenon under investigation, the above procedure was repeated 
exactly except that the flavours were reversed during Phase 2 as 
mentioned earlier. A 5-day interval was allowed to reduce the chances 
of rats confusing flavour-meal size pairings used in Phase 1 . However, 
no tests were carried out to ascertain whether or not preferences had 
remained unchanged during the intervening period. Thus, during Phase 
2 Groups V and VS were presented with anise-flavoured large meals on 
some days and vanilla-flavoured small meals on other days while Groups 
A and AS were presented with vanilla-flavoured large meals on some 
days and anise-flavoured small meals on other days. Note that these 
flavour meal size correlations are exactly the opposite to treatments 
given in Phase 1. In addition. Groups VS and AS were retained as 
controls as in Phase 1, and they both received supplements of 4 gm of 
unflavoured plain mash 15 min after the presentation of food on 'small 
meal' days. However, as in Phase I, Groups V and A did not receive 
any supplementary food on their small meal days. 

Relative preferences for anise-flavoured food in the extinction choice 
tests which followed each 8 day training cycle were calculated in terms 
of percentages of total food consumption by each subject during each 
test as follows: 

intake of anise 
intake of both anise and vanilla 



Preference for anise (%) = 100 ^ 



Data analysis 

Data obtained during each of the two phases of the experiment were 
initially assessed using separate three way analyse of variance (ANOVA) 
with repeated measures, comprising large meal flavour (anise versus 
vanilla), supplementation (supplement versus no supplement) and test 



LEICKNESS C. SIMBAYI 7 

session (Test 1 versus Test 2) as factors. In order to determine how 
flavour preferences shifted after each 8 day training cycle, data obtained 
during each of the two test sessions in each phase were also separately 
assessed using two way ANOVAs with large meal flavour and 
supplementation as factors. 



RESULTS 

During conditioning, all animals ate all of the portions of food given 
to them every day. The data obtained from the extinction choice tests 
carried out at the end of each of the four 8 day training cycles in 
Experiment 1 are illustrated in Figure 1 . This figure shows that although 
all groups highly preferred vanilla compared with anise in all choice 
tests (as revealed by low anise preferences ranging from 2 % to 35 %), 
quite clear group differences could still be seen. 




PHASE 1 



2 1 

TEST SESSIONS 



PHASE 2 



- GROUP V -t- GROUP VS -X- GROUP A "■- GROUP AS 



Figure 1. Mean preferences (%) for anise flavour during the two-jar extinction choice 
tests in Experiment 1 (n = 5). Note: Flavour-meal size pairings were reversed during 
Phase 2. 



8 INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY 

The ANOVAS performed on data obtained during each of the two 
phases of the experiment revealed a significant main effect of large meal 
flavour during Phase 1 only, F(3,16) = 5.69, p < 0.01. As can be clearly 
seen in Figure 1, this indicates that both Groups V and VS consumed 
significantly more anise-flavoured food than Groups A and AS during 
Phase 1 . However, there were no such major flavour preference shifts 
observed during Phase 2 following reversal training, although the 
direction of the small preference shifts that had occurred was similar to 
that observed during Phase 1. 

A two way ANOVA of data obtained during Test 1 of Phase 1 
revealed reliable main effects of both large meal flavour and 
supplementation, F(l, 16) = 8.17 and 5.32, p < 0.01 and 0.05, 
respectively. However, there was no significant interaction between the 
two factors. As can also be clearly seen in Figure 1, supplementation of 
meals significantly reduced the magnitude of flavour preference shifts 
during Test 1 . Another two way ANOVA of data obtained during Test 
2 of Phase 1 revealed a significant main effect of large meal flavour 
only, F(l,16) = 5.32, p < 0.05. Similar statistical analyse of data 
obtained during each of the two tests in Phase 2 of the experiment failed 
to reveal any significant main effects or interactions. 



DISCUSSION 

Three main findings emerged from Experiment 1 . Firstly, adult rats 
learned to prefer a particular flavour when it was previously correlated 
with small meals more than when the same flavour was correlated with 
larger ones. Secondly, supplementation of small meals initially slightly 
reduced the preferences for the flavour previously paired with the small 
meal, but had no effect on the preferences afterwards. Even though the 
rats had clearly a positive preference for vanilla and what appeared to be 
an unconditioned aversion to anise, it was also clear from the data that 
the flavour tracking effect was quite consistent throughout the 
experiment. Thirdly, although reverse flavour-meal size pairings reduced 
the preferences to non significance, they were still in the direction 
determined by meal sizes. 

Although the first finding appears to be consistent with Booth's 
(1972; conditioned satiety findings, the extinction testing procedure 
which was used in the present experiment was different from that 
utilised by Booth. For instance. Booth's testing procedure involved 
presenting the two test flavours one at a time whereas in the present 
experiment the testing procedure involved simultaneous (or side by side) 



LEICKNESS C. SIMBAYI 9 

presentation of the two test flavours. However, the same finding clearly 
contradicts reports by Bolles et al. (1981) and Hay ward (1983) that adult 
rats can not learn taste preferences based on differing caloric outcome. 
The second finding appears to be entirely consistent with those of 
Booth and Davis (1973) and Booth et al. (1982) who found that although 
the latter supplements failed to condition meal size per se, they did 
actually manage to condition flavour preferences. Finally, the third 
finding could be explained in terms of either overshadowing or proactive 
interference (or inhibition) of the subsequent learning during Phase 2 by 
learning which took place earlier during Phase 1. 



EXPERIMENT 2 

One criticism of the conditioned satiety hypothesis, namely that the 
animal will prefer the flavour not associated with satiety, is that it might 
instead avoid the flavour with a prolonged exposure due to an acquired 
aversion. In order to rule out this possibility, in Experiment 2 flavours 
were presented for an equal amount of time but were followed or 
preceded by different sized supplements. Therefore, for one half of the 
subjects, one flavour was followed by 4 gm while a second flavour was 
followed by 1 gm of plain mash. Hence, this procedure controlled both 
for flavour exposure time and for the disturbance factor involved when 
supplements are given after the presentation of flavour cues. Another 
important issue concerns the extent to which the relationship between the 
flavour cue and the caloric supplement could also be important, since 
cues presented at meal onset may have a different value compared with 
those at the end of the meal. In order to investigate this issue flavour 
cues were preceded by supplements for the remaining half of the 
experimental subjects. This allowed comparisons to be made to examine 
the extent to which conditioned satiety depended upon the relative 
temporal positions of flavour cues and supplements. 



METHOD 

Animals and materials 

The subjects consisted of 24 male hooded Lister rats obtained from 
the same breeding colony as in the previous experiment. They were 
aged about 160 days and weighed 325 - 480 gm at the beginning of the 
experiment. The rats had previously been used in another flavour 



10 INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY 

conditioning experiment employing the Holman (1975) procedure using 
delayed reinforcement (Simbayi, 1987), but had no experience with the 
solid reinforcer, the two flavours (i.e., vanilla and anise) and the 
conditioning procedure used in this experiment. The subjects were 
allowed about 4 weeks of ad libitum feeding prior to being given another 
2 weeks to adjust to new housing conditions and a new feeding schedule 
similar to that used in Experiment 1 . In addition, they were allowed 6 
days to accommodate to feeding on wet chow from feeding jars placed 
inside their individual cages before the actual experiment began. 

All the materials used were similar to those used in Experiment 1 . 

Procedure 

The rats were housed, watered, fed and tested exactly as in 
Experiment 1. However, some major changes were made during 
training. Discrimination training commenced at the same time of day as 
in Experiment 1 and flavours were also presented in a semi-random 
order for 8 days. The subjects were randomly divided into four groups 
(n = 6), namely. Groups VS, AS, SV and SA. Groups VS and AS 
received flavoured mash initially before supplements of plain mash were 
presented whereas supplements of plain mash preceded the presentation 
of flavoured mash in Groups S V and S A. All four groups received 1 gm 
of either vanilla or anise flavoured mash, each flavour separately for a 
total of 4 days. On any particular conditioning day, all groups received 
only one of the two flavours which served as the conditioned stimuli. 
Group VS received 4 gm of plain mash 2 min after the presentation of 
1 gm of vanilla flavoured mash on some days and only 1 gm of plain 
mash also 2 min after the presentation of 1 gm of anise flavoured mash 
on other days. Groups AS received a similar treatment to Group VS, 
except that flavour-meal size contingencies were reversed, that is, 4 gm 
of plain mash 2 min after the presentation of 1 gm of anise flavoured 
mash on some days and 1 gm of plain mash also 2 min after the 
presentation of 1 gm of vanilla flavoured mash on other days. However, 
Groups SV and SA were presented with the same flavour-meal size 
pairings, as Groups VS and AS respectively, except that the order of the 
presentation of the flavoured and plain mash were reversed. Therefore, 
Group SV received 4 gm of plain mash 5 min before the presentation of 
1 gm of vanilla flavoured mash on some days and also 1 gm of plain 
mash 2 min before the presentation of 1 gm of anise flavoured mash on 
the other days. Similarly, Group SA received the same treatment as 
Group SV, except that the flavour-meal size pairing was reversed, that 
is, 4 gm of plain mash was presented 5 min before the presentation of 



LEICKNESS C. SIMBAYI 11 

1 gm of anise flavoured mash on some days and 1 gm of plain mash 2 
min before the presentation of 1 gm of vanilla flavoured mash on other 
days. The 2-min and 5-min intervals were introduced to enable the 
animals to eat all of the initial plain and flavoured mash respectively 
before additional food was presented. This procedure was adopted to 
prevent mixing of flavoured and unflavoured food and a possible 
reduction of the potency of the conditioned stimuli due to dilution. 

Testing for changes in preferences of either anise- or vanilla- 
flavoured mash was performed using two jar extinction choice tests on 

2 consecutive days and lasted for 10 min on each day as in Experiment 
1 . Rats were simultaneously presented with 30 gm of vanilla flavoured 
mash and 30 gm of anise flavoured mash in separate jars. Both Tests 
1 and 2 were held under conditions of food deprivation similar to those 
employed during conditioning. 



RESULTS 

All animals consumed their food portions on all training days. The 
results obtained from the choice tests carried out at the end of the single 
8-day training cycle are shown in Figure 2. During Test 1, both Groups 
VS and SV which had prior exposure to large vanilla-flavoured meals 
and small anise-flavoured meals had higher preferences for anise- 
flavoured mash than Groups AS and SA which had been exposed to 
large anise-flavoured meals and small vanilla- flavoured meals. There 
was a similar pattern of group preferences during Test 2. During both 
Tests 1 and 2, Groups VS and AS (which had received cues before 
supplements) had higher preferences for anise-flavoured mash than 
Groups SV and SA, which had received flavour cues after the meal 
supplements. 

A two way ANOVA of data obtained during Test 1 revealed 
significant main effects for both large meal flavour and the timing of the 
supplement, Fs (1, 20) = 10.43 and 6.22, ps < 0.01 and 0.05, 
respectively. However, there was no significant interaction between the 
two factors. The former main effect indicates that Groups VS and SV 
had significantly higher preferences for anise-flavoured mash than 
Groups AS and SA, whereas the latter one shows that flavour cues were 
more effective as conditioned stimuli during conditioning when they 
were presented at meal onset as in Groups VS and AV than at meal 
offset as in Groups SV and SA. When data obtained during Test 2 was 
also statistically assessed, neither the main effects nor the interaction 
between the two factors were found to be significant. 



12 



INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY 







TEST 1 



TEST 2 



TEST SESSION 



GROUP VS E] GROUP AS D GROUP SV ^ GROUP SA 



Figure 2. Mean preferences (%) for anise flavour during the two-jar extinction choice 
tests in Experiment 2 (n = 6). Bars represent standard errors. 



DISCUSSION 



Three main findings emerged from Experiment 2. Firstly, it 
confirmed the finding in Experiment 1 that adult rats are capable of 
learning about flavour-meal size associations. Even when flavour- 
exposure time was controlled, the rats learned to prefer a flavour 
previously associated with a small meal better than when the same 
flavour was paired with a large meal. Secondly, flavour-meal size 
effects were stronger when flavour cues were presented at meal onset 
than at meal offset. Thirdly, the conditioned effects extinguished very 
rapidly. 

The finding that conditioned satiety effects could still emerge when 
flavour exposure time was controlled provides further evidence that 
satiety associated with the ingestion of large meals has no positive 
reinforcement properties. Similar conclusions have been arrived at by 
Van Vort and Smith (1983). The present finding also weakens the 



LEICKNESS C. SIMBAYI 13 

argument that conditioned flavour preferences observed in Experiment 
1 were due to an acquired aversion towards prolonged flavour exposure 
which was associated with large meals during conditioning. 

The second finding that flavour cues were presented at meal onset 
rather than at meal offset suggested that the cues may be more salient 
and less interfered with at the former than at the latter stage. The 
presentation of flavour cues following supplements was still effective in 
conditioning satiety but it reduced the effects considerably. It is possible 
that when supplements preceded flavour cues, they interfered with the 
learning of the discrimination between the two flavours and the 
appropriate satiety signals derived from the two meal sizes. The result 
of such interference was probably some weakening of the effects of the 
conditioning. 

An alternative explanation would be that the rats became satiated 
after consuming the supplements and perceived the appropriate satiety 
signals immediately afterwards before the flavour cues were even 
presented and perceived. Therefore, it would appear from the present 
data that the strength of any flavour-meal size conditioning is stronger 
when the flavour cues precede supplements than vice versa. This finding 
appears to contradict the findings reported by Booth and Davis (1973) 
in rats and Booth et al. (1982) in humans, where the later supplements 
failed to condition meal size per se and conditioned only flavour 
preferences at most. The third finding that the conditioned satiety effects 
were weak and extinguished rapidly was surprising when compared with 
the extreme persistency of the other types of flavour conditioning based 
phenomena (see Capaldi, Myers, Campbell & Sheffer, 1983; Logue, 
1979; Revusky, 1974; although see Simbayi, 1987). The effects had 
disappeared as early as the second test day after an 8-day conditioning 
cycle during which each flavour-meal size pairing was presented four 
times only. Perhaps, the effects could have been more persistent and 
more resistant or less susceptible to extinction with additional 
conditioning. 



EXPERIMENT 3 

Both previous experiments demonstrated flavour-meal size 
conditioning in adult rats. The aim of Experiment 3 was to test 
Hay ward's (1983) claim that rat pups are apparently capable of more 
diverse learning than adult rats. As indicated earlier, Hayward showed 
that rat pups, but not adult rats, could acquire a conditioned taste 
preference for a flavour paired with a diet that provides more calories 



14 INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY 

than another diet of equal caloric density. In particular in her 
Experiment 3, she obtained stronger conditioning of caloric effects with 
rat pups when a 4 cal/gm novel diet represented the major part of the 
animal's daily caloric intake for just 4 conditioning days. The pups were 
given unlimited access to 20 gm of the 4 cal/gm diet on one day, and 
three quarters of the previous day's consumption on alternate days. In 
order to control for differential hunger experienced on days when rats 
had inadequate food, the food supply of half of the animals was topped 
up with laboratory chow 8 h after presentation of the novel diet. Thus, 
the present experiment was meant to confirm such caloric effects by 
using a procedure almost identical to that employed by Hayward except 
for the following four minor changes which were made. Firstly, rats 
were first familiarised with the diets to reduce neophobia. Secondly, on 
small days the rats received only half of the amounts of food they 
received on large meal days to make the meal sizes more easily 
discriminable but, as indicated above, their training diets were also 
supplemented by laboratory chow pellets. Thirdly, the duration of 
testing was extended to cover a period of up to 24 h with intervals at 30 
min and 4 h instead of only after 30-min and 3-h intervals as per 
Hayward (1983). This allowed monitoring of intake rates for a period 
longer than a meal which in turn made it possible for one to distinguish 
between aversions taking place early and throughout the meal as opposed 
to those taking place later. This in turn made it possible to distinguish 
between conditioned aversion and conditioned satiety respectively. 
Finally, in order to facilitate comparisons with other experiments 
reported in the present paper, conditioning lasted for 8 days instead of 
only 4 as in Hayward's study. 



METHOD 

Animals 

Twenty four male naive Lister rat pups, 24 - 28 days old and 
weighing 46-91 gm at the beginning of the experiment, were used. 
The rat pups were weaned at the age of 2 1 days old and reared in colony 
cages (4-6 animals per cage). They had ad libitum access to dry 
laboratory chow pellets (Scientific Foods, Croydon, England) and tap 
water for 3 - 7 days before the experiment commenced. Following 
selection and assignment to groups, the weanling rats were housed 
individually in wire cages in a cage rack in an experimental room and 
had ad libitum access to water throughout the experiment. 



LEICKNESS C. SIMBAYI 15 

Materials 

The recipe for the novel diet used was identical to that utilised by 
Hayward as the high calorie food. It consisted of 50% dextrin (Sigma), 
15% calcium carbonate (chalk, East Anglia Chemicals), 2.5% mineral oil 
(liquid paraffin, British Drug Houses, now M. W. Scientific, Ltd., Poole, 
Dorset, England), 7.5% ordinary (domestic) vegetable cooking oil and 
25% lactic casein (Sigma). The diet provided approximately 4 cal/gm. 
Either vanilla or anise extract was added to the diets separately in the 
following proportions: for vanilla, 10 ml of flavour was added to 100 gm 
of the diet mixture; for anise, 0.50 ml of flavour was dissolved in 20 ml 
of water and also added to 100 gm of the diet mixture. 

Procedure 

The rats were assigned randomly to four groups (n = 6), namely. 
Groups R-A, R-V, Ad-A, and Ad-V, with R and Ad standing for 
restricted and ad libitum conditions respectively, as explained below. 
Groups R-A and R-V represented Groups A and V in Experiment 1 in 
the present study whereas Groups Ad-A and Ad-V represented Group 2 
(the chow group) in Experiment 3 reported by Hayward (1983). On 
familiarisation days, all the weanling rats were exposed to the 
unflavoured novel 4 cal/gm diet. First, all groups received 40 gm 
overnight. Then, Groups R-A and R-V received only 5 gm while 
Groups Ad-A and Ad-V continued to receive unrestricted access to 40 
gm for every 24 h beginning at 1200 hrs for the next 3 consecutive days. 

On conditioning days, Groups R-A received anise flavour in 5 gm 
of the novel 4 cal/gm diet on some days and vanilla flavour in 1 gm of 
the same diet on other days. The flavour-meal size pairing was reversed 
for Group R-V. Group Ad-A received anise flavour in 20 gm of the 
novel 4 cal/gm diet on some days and vanilla flavour in 10 gm of the 
same diet on other days. Similarly, the flavour-meal size pairing was 
reversed for Group Ad-V. Therefore, for all rats, the two flavours were 
correlated with the same pattern of oral cues but differing caloric 
consequences (i.e., 20 vs. 4 calories for Groups R-A and R-V and 80 vs. 
40 calories for Groups Ad-A and Ad-V, both respectively). Altogether, 
rats in Groups Ad-A and Ad-V experienced 4 days with sufficient food 
(i.e., large meals) and another 4 days with an inadequate amount of food 
(i.e., small meals). In order to avoid the problem of differential hunger 
on days of inadequate food, the food supply was supplemented by 5 
pellets of dry laboratory chow (weighing approximately 10 gm and 
containing 40 calories) 5 h after the presentation of the training diet. 



16 INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY 

For both Groups R-A and R-V, laboratory chow was removed 2.5 h 
prior to the presentation of the novel diet and returned 5 h afterwards. 
The remaining rats in both Groups Ad-A and Ad-V received no 
additional food except only as specified above, that is, on small meal 
days. Flavours were also presented in semi-random order as in previous 
experiments. 

All groups were given an extinction choice test between the anise 
and vanilla flavoured diets on Day 9. Two jars of the 4 cal/gm food 
were presented simultaneously, and consumption was recorded at the end 
of 30 min, 4 h and 24 h for all four groups. As in previous experiments, 
preferences for anise-flavoured food were calculated as percentages of 
total food intake. 

Data analysis 

The data were first assessed using a three way repeated measures 
ANOVA with the following factors: duration of exposure to the training 
diet (restricted vs. ad libitum), the large meal flavour (anise vs. vanilla) 
and cumulative test intervals (30 min vs. 4 h vs. 24 h). Follow up 
limited pair-wise comparisons between groups trained under similar 
conditions of exposure to the training diets at each test interval were also 
carried out using independent t tests. 



RESULTS AND DISCUSSION 

All animals completely consumed their food portions on all training 
days. Figure 3 outlines the results obtained during the three cumulative 
intervals of the extinction choice test held on Day 9. It shows that the 
two groups which had received vanilla flavour paired with the larger 
meal during training (i.e., Groups R-V and Ad-V) generally had higher 
preferences for anise than the other two groups (i.e., Groups R-A and 
Ad-A) which had received anise paired with the larger meal during 
training. This effect was particularly marked after 24 h than after both 
the 30 min and 4 h cumulative intervals of the extinction choice test. 

The repeated measures ANOVA failed to reveal any significant main 
effects (all ps > 0.05). However, the interaction between all three factors 
was significant, F(2,40) = 5.82, p < 0.01. Additional between-group 
comparisons also revealed a highly significant difference between 
Groups Ad-A and Ad-V after 24 h of testing only, / (10, one tailed) = 
5.07, p < 0.001 (see Figure 3). This shows that the rat pups were clearly 
capable of learning to associate a taste with the size of the meal under 



LEICKNESS C. SIMBAYI 



17 




30 MIN 



4 HOURS 
TEST INTERVAL 



24 HOURS 



GROUP R-A E] GROUP R-V D GROUP Ad-A ^ GROUP Ad-V 



Figure 3. Mean preferences (%) for anise flavour during the two-jar extinction choice 
tests in Experiment 2 (n = 6). Bars represent standard errors. 



the ad libitum feeding conditions, whereas they were not able to do so 
under restricted feeding conditions. Even more interesting was the fact 
that flavour preference shifts were most pronounced after 24 h of testing 
than earlier. This finding suggests that the flavour-meal size 
conditioning effects observed in these experiments might be attributed 
to satiety rather than aversions, because if the latter were involved, 
flavour preference shifts would have been observed throughout the test 
period. In particular, they would have commenced at the beginning of 
the test period rather than later, as occurred in the present experiment. 
The results are consistent with Booth's (1972) conditioned satiety ideas 
but they clearly contradict Hayward's (1983) findings. It is important to 
note here that the present experiment used a procedure similar to 
Hayward's except that the meal sizes and one flavour were different. 
However, her findings generally supported a conditioned appetite 
hypothesis whereby only young rats learned to prefer a taste which was 
previously associated with larger meal sizes or more calorific diets. 



18 INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY 

EXPERIMENT 4 

As both the training and testing procedures employed in Experiment 
3 did differ somewhat from those employed in both earlier experiments 
(i.e., Experiments 1 and 2), it is not only difficult but also rather unfair 
to make direct comparisons between their respective findings. Clearly, 
the best way to achieve such a goal would be to replicate Experiment 3 
using naive adult rats. This was the aim of Experiment 4. According 
to Hay ward (1983), an adult rat no longer attends to post-ingestional 
feedback since it is rarely hungry and therefore is not capable of learning 
conditioned taste preferences based on differing caloric outcome. 
Therefore, Experiment 4 investigated whether naive adult rats could be 
as responsive as naive young rats to flavours paired with differing 
caloric outcome when novel diets provided either only a small proportion 
or most of the rats' daily caloric needs. 

METHOD 

Animals 

Twenty four naive male hooded Lister rats 81 - 126 days-old and 
weighing 245 - 420 gm at the start of the experiment were used. 

Materials and Procedure 

The materials and procedure were the same as for Experiment 3 
except for the following three minor changes: both Groups R-A and R- 
V were allowed 25 gm of supplementary solid laboratory chow pellets 
at 17.00 hrs each day; during familiarisation, both Groups Ad-A and 
Ad-V received 30 gm of unflavoured and novel high calorie diet instead 
of 20 gm only as in Experiment 3; during training, both Groups Ad-A 
and Ad-V received 30 gm of the novel diet with no supplements on 
large meal days and 15 gm of the novel diet plus another 15 gm 
supplement of solid laboratory chow pellets on small meal days. All the 
changes were made to compensate for the larger size of animals used in 
the present experiment compared to those used in Experiment 3. 



RESULTS AND DISCUSSION 

All animals completely consumed their food portions on all training 



LEICKNESS C. SIMBAYI 



19 




30 MIN 



4 HOURS 
TEST INTERVAL 



24 HOURS 



GROUP R-A E] GROUP R-V DgROUP Ad-A ^ GROUP Ad-V 



Figure 4. Mean preferences (%) for anise flavour during the two-jar extinction choice 
test in Experiment 3 (n = 6). Bars represent standard errors. 



days. The results obtained during the three interval of the extinction 
choice test held on Day 9 are displayed in Figure 4. They show that 
Group Ad-V generally had higher preferences for anise flavour than 
Group Ad-A, whereas no such differences are evident between Groups 
R-A and R-V. 

When the data were assessed using a three way repeated measures 
ANOVA as for Experiment 3, neither the main effects nor interactions 
were significant. However, additional between-group comparisons of 
anise preferences indicated that Group Ad-A had a significantly higher 
preference than Group Ad-V after the 4 h test interval only, / (10, one 
tailed) = 2.20, p < 0.05. Thus, these mature rats were also able to learn 
about flavour-meal size associations under ad libitum but not restricted 
feeding conditions, as did the weanling ones in Experiment 3. It is 
rather difficult to explain why adult rats appeared to learn conditioned 
satiety only when flavour-meal size pairings were presented on an ad 
libitum basis (30 gm vs. 15 gm) but not when access was restricted to 



20 INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY 

much smaller amounts (5 gm vs. 1 gm). Perhaps, in the latter condition 
adult rats simply ignored post-ingestional feedback of the small snacks 
with a novel flavour and concentrated mostly on the bigger 
supplementary meals from which most of their daily caloric requirements 
were derived. Such a view is consistent with that of Bolles et al. (1981) 
and Hay ward (1983) who used this fact to argue why adult rats should 
fail to learn to associate a flavour with a diet that provides more calories 
under such conditions. Nevertheless, the fact that, like weanling rats, 
adults can acquire flavour-meal size effects, appears to contradict these 
authors' findings. Another interesting aspect of the present results is that 
preference shifts in those groups which displayed them were most 
evident only after 4 h of testing. This differs from Experiment 3 where 
preference shifts were most notable in the groups concerned after 24 h 
of testing. Although the reasons for this disparity are unclear at present, 
one possibility is that older rats may experience the onset of satiety 
much sooner than younger ones. Nevertheless, this issue needs to be 
investigated further. Experiment 4, therefore, has shown that adult rats 
appear to learn to make flavour-meal size associations just as well as 
weanling rats especially when the diet provides for most of the animals 
daily caloric needs. 



GENERAL DISCUSSION 

The present research showed that both weanling and mature rats are 
capable of learning to associate a flavour with the size of a meal. In 
particular, these findings demonstrated flavour-meal size conditioning 
effects whereby an animal learns to prefer a flavour not associated with 
a larger meal. It is however important to note here that, as Capaldi and 
Myers (1982) and Davidson-Codjoe and Holman (1982) have pointed 
out, the preferences demonstrated in experiments of this sort are relative, 
rather than absolute. The data really do not distinguish a preference for 
the flavour consumed when rats received the small meal from an 
aversion for the flavour consumed when they received the large meal. 
Furthermore, as Capaldi et al. (1983) also pointed out, the word 
"preference" is usually intended as a neutral term accommodating either 
a learned aversion for the flavour associated with the large meal, learned 
liking for the flavour associated with the small meal, or both. 

As the present results are consistent with Booth's (1972) and Booth 
and Davis' (1973) findings, a phenomenon very similar to Booth's 
conditioned satiety may be implicated. Conditioned satiety involves an 
increment in the size of the feeding bout on the dilute nutrient (or, small 



LEICKNESS C. SIMBAYI 21 

meal, few calories, etc.) more than on the more concentrated nutrient (or 
large meal, many calories, etc.) after several pairs of presentations. This 
takes place in order to compensate for calories depending on the nature 
of the concentrated diet. Booth suggested that such conditioning of 
satiety may be important in the control of food intake only under 
conditions which are put on the timing of meals, that is, under high food 
deprivation schedules. Perhaps, different mechanisms are involved under 
normal ad libitum feeding conditions. This might explain why stronger 
evidence of conditioned satiety learning was obtained under restricted 
feeding conditions in both Experiments 1 and 2 in the present study than 
was the case under ad libitum feeding conditions in both Experiments 3 
and 4. Nevertheless, the present findings clearly demonstrated the 
existence of an acquired oral and/or olfactory sensory control of the 
satiation process just as Booth's conditioned satiety study did. The 
present findings are also in agreement with those of Le Magnen (1985) 
and Deutsch (1982). 

The present findings suggest that oral qualities of a familiar food 
may enable a mammal to react in anticipation of that food's caloric value 
or the duration of its satiating effect. According to such a view, animals 
stop eating at an appropriate stage even though absorption has barely 
started or possibly has not even started at all as in the case of a rapid 
feeder such as a dog. However, our findings clearly contradict 
Hay ward's (1983) findings which generally demonstrated conditioned 
appetite in weanling rats but not in adults. Apart from strain differences, 
it is unclear at present why our results contradict Hayward's. 

One hypothesis which explains the present findings is that the 
flavour tracking may be due to an acquired difference in the 
development of feeding inhibition during meals. This is because there 
were no differences in basal acceptability since both meals consisted of 
the same diet, except for flavours which were added to them. This view 
is consistent with that of Booth (1972). The higher preference for the 
flavour which had been paired with a small meal demonstrated in the 
present study could be attributed to a difference in the speed of onset of 
the suppression of intake in the later stages of the meal. This might 
suggest that an acquired oral and/or olfactory factor contributed to the 
development of the satiety which ended the meal to which the flavour 
previously associated with the large meal was added. When faced with 
a choice between flavour cues previously associated with large and small 
meals during conditioning, a satiety signal switched off eating 
immediately after the animal had perceived that the flavour was 
previously correlated with a large meal which was too satiating. 
However, there was no such satiety signal forthcoming from flavour 



22 INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY 

correlated with less satiating small meals and consequently, rats 
consumed significantly more food with a flavour which was previously 
associated with a small, less satiating meal. Hence, satiety had no 
positive reinforcing effects and might have been aversive. As was 
mentioned earlier, such a conclusion is consistent with that of Van Vort 
and Smith's (1983) who found that satiety had no positive reinforcing 
effects on flavour preferences at all whilst using sham feeding techniques 
and a similar flavour tracking procedure. 

An alternative explanation is that when rats were exposed to flavours 
correlated with large meals, they developed slightly stronger aversions 
to them than when exposed to flavours correlated with small meals. 
However, since Experiments 2-4 controlled for the amount of flavour 
exposure, this hypothesis is highly improbable. Furthermore, the mere 
fact that all groups in Experiment 1 ate in excess of 60% vanilla- 
flavoured food during choice tests further weakens this argument. 

The conditioning of flavour preferences based on meal size 
demonstrated in the present research does not in any way contradict Le 
Magnen's (1969) findings of conditioned appetite at all. Conditioned 
discriminative (also referred to as selective or differential) appetite 
induced during conditioning causes a rat to eat more of the reinforced, 
and hence beneficial food, and less of the non reinforced food in the 
final choice test. As Bolles et al. (1981) pointed out, conditioned satiety 
and conditioned appetite merely represent complementary aspects of 
intake regulation. Whereas the phenomenon proposed by Le Magnen 
(which Bolles et al. later failed to demonstrate) was basically concerned 
with food selection through learning about the caloric potential of 
different foods, the phenomenon demonstrated in the present study more 
likely operates after the selection of the diet offering optimum caloric 
consequences has been completed. Hence, the animal learns to eat less 
of that diet on a day-after-day basis under conditions in which 
constraints are put on the timing of meals. 

According to Capaldi et al. (1987), shifts in preferences such as 
those demonstrated in the present study can be viewed within either a 
classical conditioning or an instrumental learning paradigm. In a 
classical conditioning framework, the flavours are the conditioned stimuli 
(CSs) and they are being associated with some unconditioned stimulus 
(US) that is produced by consumption of meals of different sizes made 
from the same diet. In an instrumental learning paradigm, the flavours 
are the discriminatory stimuli (SDs) signalling the reinforcement 
produced by the instrumental response of consuming meals of different 
sizes. The important question therefore concerns what is the US or 
reinforcer in either paradigm. 



LEICKNESS C. SIMBAYI 23 

One of the best candidates for the US or reinforcer in the type of 
learning demonstrated in the present study is the post-ingestive 
consequences of ingesting meals such as calories. Supporting evidence 
for flavour-calorie learning in rats has been reported elsewhere (e.g., 
Capaldi et al., 1987; Deems et al., 1986; Hayward, 1983; Holman, 1975; 
Mehiel and Bolles, 1984; Sherman, Hickis, Rice, Rusiniak & Garcia, 
1983). Another possible candidate for the US or reinforcer is some oral 
stimulus such as flavour (or taste). However, this is very unlikely 
because the different sized meals in each experiment in the present study 
consisted of exactly the same diet, which meant that the flavour of the 
food contained in the two meals was identical. Thus, the flavour-meal 
size conditioning effects demonstrated in the present research were most 
probably the result of flavour-calorie rather than flavour-flavour 
associations. 

Finally, it must be noted here that although only four experiments 
are reported in the present paper, six additional experiments were also 
carried out which consistently failed to yield any significant effects. 
However, preferences were mainly in the direction which is predicted by 
the conditioned satiety hypothesis, that is, the small meal flavour was 
relatively more preferred. These findings also suggest that the 
flavour-meal size conditioning effect definitely occurs but we have not 
yet been able to identify all the conditions which enable consistently 
reliable effects. 

In conclusion, both mature and weanling rats appear to be capable 
of learning about flavour-meal size associations. In particular, they 
acquired conditioned satiety, albeit very weakly, rather than conditioned 
appetite as previously demonstrated by both Bolles et al. (1981) and 
Hayward (1983) in their similar studies. These conditioned satiety 
effects, which are most probably due to flavour-calorie rather than 
flavour-flavour (or tastes) associations, are also distinctly elusive. 



ACKNOWLEDGEMENTS 

This research was carried out in the Laboratory of Experimental 
Psychology at the University of Sussex, Brighton, England, U.K., as part 
of a D. Phil, project. It was partially financed by a U.K. Medical 
Research grant to Dr. M.J. Burton and also by a University of Zambia 
Staff Development Fellowship to the author. The author wishes to 
acknowledge, with deep gratitude, the immense help received during the 
study from Drs. Burton and R. A. Boakes, both of the Laboratory of 
Experimental Psychology at Sussex University at the time, who jointly 



24 INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY 

served as supervisors for this project. Their constant encouragement 
throughout his sojourn at Sussex University is especially appreciated. 
The author would also like to thank Sara Hill, Tracey Gummet, 
Annabele Poate and Mark Allen for helping carry out Experiment 2 as 
part of their undergraduate research project under his supervision and 
also Dr Christopher J. Rainey for his assistance with running some of the 
experiments. Finally, the comments and suggestions of two anonymous 
reviewers are greatly appreciated. 



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psychology (Vol. 4). New York: Academic Press. 
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Boakes, D.A. Popplewell, & M.J. Burton (Eds.), Eating habits. Chichester: John 

Wiley. 
Le Magnen, J., Marfaing-Jallat, P., & Miceli, D. (1980). A bioassay of 

ethanol-dependence in rats. Pharmacology, Biochemistry and Behavior, 12, 

707-709. 
Logue, A.W. (1979). Taste aversion and the generality of laws of learning. Psychological 

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26 INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY 

Marfaing-Jallat, P., & Le Magnen, J. (1979). Ethanol-induced taste aversion in 

ethanol-dependent and normal rats. Behavioral and Neural Biology, 26, 106-114. 
Mehiel, R., & Bolles, R.C. (1984). Learned flavour preferences based on caloric 

outcome. Animal Learning and Behavior, 12, 421-427. 
Revusky, S.H. (1967). Hunger level during food consumption: Effects on subsequent 

preference. Psychonomic Science, 7, 109-110. 
Revusky, S.H. (1968). Effects of thirst level during consumption of flavoured water on 

subsequent preference. Journal of Comparative and Physiological Psychology, 66, 

111-119. 
Revusky, S.H. (1974). Retention of learned increase in the preference for flavoured 

solution. Behavioral Biology, 11, 121-1254. 
Riley, A.L., & Tuck, D.L. (1985). Conditioned taste aversions: A bibliography. In N.S. 

Braveman, & P. Bronstein (Eds.), Experimental assessments and clinical 

applications of conditioned food aversions. Annals of the N.Y. Academy of Science, 

443, 381-437. 
Rozin, P. (1977). The significance of learning mechanisms in food selection: Some 

biology, psychology and sociology of science. In L.M. Barker, M.R. Best, and M. 

Domjan (Eds.), Learning mechanisms in food selection. Waco, Texas: Baylot 

University Press. 
Sherman, J.E., Hickis, C.F., Rice, A.G., Rusianik, K.W., & Garcia, J. (1983). Preferences 

and aversions for stimuli paired with ethanol in hungry rats. Animal Learning and 

Behavior, 77, 101-106. 
Simbayi, L.C. (1987). Immediate and delayed flavour-calorie learning. Can rats do it? 

International Journal of Comparative Psychology, 1, 58-77. 
Simbayi, L.C, Boakes, R.A., & Burton, M.J (1986). Can rats learn to associate a flavour 

with the delayed delivery of food? Appetite, 7, 41-53. 
Smith, G.P., & Gibbs, J. (1979). Postprandial satiety. In J.M. Sprague, & A.N. Epstein 

(Eds.), Progress in psychobiology and physiological psychology (vol. 8). New York: 

Academic Press. 
Van Vort, W., & Smith, G.P. (1983). The relationships between the positive reinforcing 

and satiating effects of a meal in the rat. Physiology and Behavior, 30, 279-284. 



Internationa! Journal of Comparative Psychology, Vol. 7, No. 1, 1994 



LIGHT MEDIATION OF CIRCADIAN 
PREDATORY BEHAVIOR IN THE YOUNG 

ALLIGATOR 

Jack A. Palmer 

Linda K. Palmer 

Northeast Louisiana University 



ABSTRACT: Minnow predation by 10 young American alligators (Alligator 
mississippiensis) was systematically measured during four daily time periods under 
four different conditions of lighting in order to investigate a circadian rhythm of 
predatory behavior. The four daily time periods were night (1:00 a.m. -7.00 a.m.), 
morning (7.00 a.m.- 1:00 p.m.), afternoon (1:00 p.m.-7:00 p.m.), and evening (7:00 
p.m. -1:00 a.m.). Each of the following lighting conditions had a duration of 4 weeks: 
continuous complete darkness (DD); continuous artificial illumination (LL); naturally 
varying Ught-dark conditions (natural LD); and reversed light-dark conditions with 
artificial lights on at sunset and off at sunrise (reversed LD). Predatory behavior (i.e., 
the number of prey fish consumed wholly or partially during each test session) varied 
significantly as a function of the interaction between time period and lighting 
condition. Under natural LD, the mean number of prey killed during night sessions 
was significantly higher than either morning or afternoon sessions. Under reversed 
LD, the pattern of predation reversed from that exhibited under normal Ughting, with 
both morning and afternoon predation significantly higher than either evening or 
night. Under conditions of continuous illumination (LL and DD) the natural LD 
circadian pattern persisted for over 1 week with significantly higher predation rates 
during the night periods as compared to the morning and afternoon periods. The 
gradual transition of predation pattern in response to manipulations of the light-dark 
cycle suggests that the circadian rhythm of alligator predadon is dependent upon 
light-dark variation for entrainment. 



INTRODUCTION 

The adult American alligator {Alligator mississippiensis) has been 
described as an opportunistic scavenger as well as an active predator 



Address correspondence to Jack A. Palmer, Department of Psychology, 
Northeast Louisiana University, Monroe, LA 71209, USA. 

© 1994 International Society for Comparative Psychology 27 



28 INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY 

(Mcllhenny, 1976; Pooley, 1989; Weldon, Swenson, Olson, & 
Brinkmeier, 1990). Hatchling alligators eat insects, small crustaceans, 
and small fish (Coulson & Hernandez, 1983), whereas adult alligators 
prey upon frogs, snakes, birds, muskrats, nutria, and larger mammals 
(Mcllhenny, 1976; Pooley, 1989; Ross & Magnusson, 1989; Scott & 
Weldon, 1990). The alligator is generally considered a nocturnal 
species with most of its feeding behavior and general activity taking 
place during the night (Lang, 1976; Mcllhenny, 1976; Murphy, 1981; 
Pooley, 1989). Alligator predatory behavior appears to follow a 
circadian rhythm, but this has not been systematically investigated and 
reported. 

In almost all vertebrates, endogenous circadian rhythms regulate 
temporally certain types of behavior (e.g., sleep) and bodily functions 
(e.g., hormone secretions, Aschoff, 1989). The rhythm itself is often 
entrained or synchronized by environmental cues such as daily cycles 
of light-dark and temperature change (Aschoff, 1989; Griffiths, 1986). 
These environmental cues that set the timing of circadian behavior are 
referred to as zeitgebers (Aschoff, 1989). Aschoff reports that the 
most powerful of all zeitgebers is a light-dark cycle. In the absence 
of zeitgebers (e.g., an environment of continuous darkness), circadian 
rhythms are free-running and self-sustaining. The free-running 
rhythm may cycle every 24 hours, be slightly longer, or slightly 
shorter. 

In lower vertebrates, light mediates circadian rhythm via the 
photosensitive pineal gland. Although alligators lack pineal glands, 
studies have indicated that some circadian rhythms in alligators are 
controlled or mediated by light cycles. Circadian rhythm of young 
alligator motor activity was documented by Kavaliers and Ralph 
(1980). Lang (1976) found that movement between land and water in 
juvenile alligators varied as a function of circadian rhythm cued by 
light-dark cycles. A study by Murphy (1981) indicated the existence 
of an endogenous clock synchronized by the circadian light-dark cycle 
which enabled young alligators to use solar compass orientation. 
Kavaliers (1980) demonstrated that extraretinal responses to light 
pulses varied according to circadian phase. Moreover, photoperiod 
manipulation indicated exogenous entrainment of the extraretinal 
responses by light-dark cycles. In light of the alligators' lack of a 
pineal gland, Kavaliers and Ralph (1981) argued that overall 
organization of circadian rhythm and period length depends on a 
complex interaction of retinal inputs, extraretinal inputs, and other 
neural areas. 

This study sought to determine if alligator predation was subject 



JACK PALMER AND LINDA PALMER 



29 



to circadian rhymicity. Minnow predation (i.e., number of minnows 
wholly or partially consumed) by young alligators was systematically 
measured during four daily time periods under different conditions of 
lighting. It was hypothesized that predation rates would peak during 
the dark periods of 24-hour natural and reversed light-dark cycles, and 
that an endogenous circadian rhythm would persist under continuous 
illumination. It was predicated that the circadian fluctuation could be 
altered by manipulating the light-dark cycle, thus supporting 
dependence upon light-dark alternation as a zeitgeber. A gradual 
transition of predation pattern in response to light-dark cycle 
manipulations would indicate entrainment by a light-dark zeitgeber. 

TABLE 1 

Subject Size After the Study Compared with Number of Prey 

Captured During 6-Hr Sessions 





Subject Size 


Number of Prey 










Captured 
Range 


Mean 




Subject 


Length 


Weight 


SD 


1 


46.0 


304.0 


0-9 


1.89 


2.28 


2 


46.5 


285.5 


0-10 


2.77 


2.94 


3 


42.5 


215.0 


0-10 


2.57 


2.97 


4 


42.5 


203.5 


0-10 


2.36 


2.78 


5 


41.9 


208.5 


0-10 


2.28 


2.84 


6 


38.5 


176.5 


0-9 


2.16 


2.37 


7 


39.0 


164.0 


0-6 


1.59 


1.84 


8 


44.0 


228.5 


0-10 


2.71 


2.94 


9 


37.0 


148.5 


0-5 


1.65 


1.73 


10 


38.0 


151.5 


0-10 


2.08 


2.48 



METHOD 
Subjects 



Ten 1990 hatchling alligators {Alligator mississippiensis), 27 to 29 
cm in length and weighing 56 to 80 gm, were obtained from the 
Rockefeller Wildlife Refuge, Grand Chenier, Louisiana when they 



30 INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY 

were approximately 1 month of age. (Age is approximate because 
exact date of hatching is not known). Testing began when subjects 
were approximately 6 months old and continued until subjects were 
approximately 14 months old. At the completion of testing, subjects 
ranged from 37 to 46 cm in length and 148.5 to 304 gm in weight 
(Table 1). Individual subjects were identified by removing a specific 
tail scute. 

Maintenance 

When not being tested, all 10 alligators were maintained in a 
home pool measuring 45.72 cm deep and 2.44 m in diameter. Ten 
cm of water covered the bottom, and a 60.96 cm diameter gravel- 
surfaced concrete "island" was situated near the center of the pool. 
The pool was retained in a heated- enclosed garage with windows 
facing north and east. Air temperature ranged from 21 to 28°C with 
an average of 25°C. Water temperature ranged from 20 to 27°C with 
an average of 24°C. The pool was drained and filled with fresh water 
as necessary (usually once each week). 

Food included two species of live minnows (Notropis cornutus 
and Cyprinus Idas idus) and Burris Alligator Feed. Alligators were 
permitted to obtain live prey (minnows) beginning when they were 2 
months old. Once testing began, live prey was available only in the 
testing arenas during test sessions. Burris Alligator Feed was 
provided ad libitum in the home pool. 

Live minnows were obtained as needed (about every 2 weeks) 
from local bait shops and fish supply outlets. They were maintained 
in a plastic barrel, 55.88 cm in diameter and 71.12 cm high, filled 
with water. Aeration was furnished by an electric Second Nature 
Whisper 400 aquarium pump. Water and air temperature were the 
same as that for the alligators. The minnows were fed an adequate 
amount of Wardley Tropical Flakes fish food every evening. 

Apparatus 

Each test arena consisted of a plexiglass tray 45.72 cm x 25.4 cm 
X 12.7 cm high with a grill-type metal lid that allowed air circulation 
but prevented escape. Each arena was filled with 7.62 cm of water. 
The test arenas were located in the same room as the alligator home 
pool. Water temperature was the same as that in the home pool. 



JACK PALMER AND LINDA PALMER 31 

Procedure 

All subjects were tested under all conditions. A two-factor (4 x 
4) within-subjects experimental design was used, with one factor 
(daily time period) nested within the other factor (lighting condition). 

The four lighting conditions were continuous complete darkness 
(DD), continuous artificial illumination (LL), naturally varying light- 
dark (natural LD), and reversed light-dark with artificial light on at 
sunset and off at sunrise (reversed LD). Each lighting condition was 
maintained for 4 weeks, and each followed a 2-week period of natural 
lighting to control for carryover effects. (Kavaliers and Ralph [1980] 
demonstrated that, following light manipulation, 10 days of natural 
light were sufficient to restore normal circadian rhythmicity of 
alligator motor activity). 

Artificial illumination was provided by a Power-Glo 40-watt full 
spectrum fluorescent lamp. When necessary to shut out natural light, 
the windows were covered with black shades taped tightly against the 
walls so that no light could enter. 

A total of 640 predation test sessions of 6-hour duration were 
conducted (160 test sessions per lighting condition). Predation test 
sessions were alternated randomly among four time periods: night 
(1:00 a.m.-7:00 a.m.), morning (7:00 a.m.- 1:00 p.m.), afternoon (1:00 
p.m. -7:00 p.m.), and evening (7:00 p.m.- 1:00 a.m.). No time period 
was repeated until the other three had been used. All four time 
periods were tested each week. 

Because movement between land and water has been 
demonstrated to follow a circadian pattern itself (Lang, 1976), 
alligators and prey animals were placed in test arenas to control for 
this possible confound. Each test session was conducted as follows: 
ten minnows, five specimens each of Notropis cornutus and Cyprinus 
idus idus, were moved with a net by the investigator from their home 
barrel to a test arena at the beginning of the designated 6-hr time 
period. An alligator was then carried by the investigator by hand 
from its home pool to the test arena. A grill-type metal lid was then 
placed on the test arena. During the 6-hr test session, the animals 
were not disturbed. At the end of the session, the number of prey 
killed (i.e., number of minnows missing or partially consumed) was 
recorded. The alligator and remaining minnows (if any) were then 
returned to their respective homes. The water in the test arena was 
emptied and replaced with fresh water after each test session. 



32 
RESULTS 



INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY 



The dependent variable, number of minnows consumed wholly or 
partially, was analyzed with a repeated measures analysis of variance 
(ANOVA), in which time period and lighting condition were 
independent variables (both repeating) with time periods nested within 
lighting conditions. Predatory behavior varied significantly as a 
function of the interaction between time period and lighting condition, 
F(9,270) = 15.79, /?<.001. Mean prey killed for each time period 
within each lighting condition are reported in Table 2. 

TABLE 2 

Means and Standard Deviations of Prey Killed During Time 

Periods Under Different Lighting Conditions 







Time Periods 




Lighting Conditions 


Night 


Morning 


Afternoon 


Evening 


Continuous Dark 










Mean 


0.393 


0.260 


0.065 


0.203 


SD 


(0.507) 


(0.404) 


(0.227) 


(0.377) 


Continuous Light 










Mean 


2.775 


2.975 


2.800 


2.350 


SD 


(2.769) 


(3.109) 


(2.757) 


(2.107) 


Natural Light 










Mean 


2.700 


1.300 


1.250 


2.075 


SD 


(2.221) 


(1.488) 


(1.256) 


(1.542) 


Light Reversal 










Mean 


2.600 


4.500 


4.600 


1.750 


SD 


(1.646) 


(2.491) 


(3.177) 


(1.932) 



Figure 1 compares the predation patterns that occurred under 
natural LD and reversed LD cycles. Tukey HSD multiple 
comparisons showed that under natural LD the mean number of prey 
killed at night was significantly higher than either morning (p<.0\) or 
afternoon (p<.0\). Although mean number of prey killed was higher 
during evening than either morning or afternoon, the differences were 



JACK PALMER AND LINDA PALMER 33 



40 -1 



5 30 



0) 



0) 

^ 20 

o 

u 



10 




Natural LD 
Reversed LD 



' I 1 I I 

Afternoon Evening Night Morning 



Figure 1. Circadian predatory behavior patterns under lighting conditions 
natural and reversed LD. 



not significant. Kill rates for evening and night sessions did not differ 
significantly from each other. Morning and afternoon kill rates also 
did not differ significantly from each other. 

Under reversed LD conditions, the pattern of predation reversed 
from that exhibited under natural LD. Tukey HSD multiple 
comparisons revealed that morning predation was significantly higher 
than either night (p<.00\) or evening predation (p<.00l). Afternoon 
predation was also significantly higher than either night (p<.00\) or 
evening predation (p<.00\). The reversed LD condition produced no 
significant differences between morning and afternoon predation. 
However, night predation was significantly higher than evening 
predation (p<.05). 

Under DD, night predation was significantly higher than afternoon 
predation (p<.01). Under LL, no significant differences were found 
among the time periods. 

The data for the initial week under each of the two constant 
conditions, LL and DD, were examined to see to what degree the 
natural LD pattern persisted. Figure 2 illustrates that the natural 
predation pattern did persist during the first week of LL and DD with 
predation rates peaking during night periods. Tukey HSD multiple 
comparisons determined the following significant differences. Under 
DD, night predation was significantly higher than after noon (p<.Q5) 



34 



INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY 




Afternoon Evening Night Morning 



Figure 2. Circadian rhythm of predation during the first week of LL, DD, and 
natural LD conditions. 



predation. Under LL, night predation was significantly higher than 
morning (jx.Ol), afternoon (p<.0\), and evening (p<.05) predation. 

Table 1 displays the mean number of prey killed by each subject. 
Predation rates of the 10 subjects were analyzed with a one-way 
ANOVA to determine if predation differed among subjects. No 
significant differences were found. 



DISCUSSION 



Alligators as young as 2 months of age are capable of capturing 
very active prey. The evidence accrued in this study suggests that 
predatory behavior in the young alligator varies as a function of light- 
mediated circadian rhythm. Light plays a critical role, as predation 
during dark periods was significantly higher than during light periods, 
whether lighting conditions were natural or reversed. Predation rates 
during natural and reversed LD climaxed during the second 
contiguous time period of darkness (i.e., night period of natural LD 
and afternoon period of reversed LD). This suggests that, in the wild, 
predatory behavior of the young alligator reaches a peak during the 
hours before dawn, declines sharply after daybreak, remains low 
throughout the day, and then rises steadily after nightfall. Such an 



JACK PALMER AND LINDA PALMER 35 

activity cycle is similar to the circadian rhythms of alligator motor 
activity found in other research (Kavaliers, 1980; Kavaliers & Ralph, 
1980, 1981; Lang, 1976). 

Aschoff (1989) describes circadian rhythms as "self-sustaining 
oscillations", and the test for such persistence is a recording of the 
activity under continuous non-varying illumination. Under DD, a 
predation pattern similar to natural LD persisted (i.e., night predation 
was significantly higher than afternoon), although predation was 
relatively suppressed during all time periods (see Table 2). 
Examination of predation rates of the first week under conditions of 
LL and DD showed that a general pattern of circadian rhythm, similar 
to the natural LD pattern, persisted. During the second week of LL, 
the pattern became arhythmic. This is in accord with Kavaliers and 
Ralph's (1980) study where the free-running circadian rhythm of 
alligator motor activity became arhythmic after 10-15 days of LL. 

The suppression of predation during DD may have been due to 
melatonin, a hormone that increases during periods of darkness 
(Galluscio, 1990) and appears to regulate cycles of sleep and activity 
in many animals (Wurtman & Lieberman, 1987). Melatonin is 
present in the blood of alligators (Gern, Owens, Ralph, & Roth, 
1978), but its exact role is not known. In birds, the increase in 
melatonin appears to cause a decrease in activity and in body 
temperature (Binkley, 1979). Although alligators are poikilotherms, 
an increase in melatonin due to continuous darkness may suppress 
predatory behavior. 

Figure 3 provides further evidence of an endogenous circadian 
rhythm of predatory behavior. If the temporal occurrence of the 
young alligator's predatory behavior was solely under light stimulus 
control with no endogenous circadian rhythm, then an abrupt change 
in predatory behavior should occur immediately following light 
reversal. However, Figure 3 demonstrates a gradual transition of 
predation pattern in response to reversed LD, more indicative of a 
circadian rhythm being reprogrammed by the zeitgeber than behavior 
cued directly by light. Alligator predation follows a circadian rhythm 
and appears to be dependent upon light-dark variation for entrainment. 

As an ancient species that has evolved in latitudes subject to 
seasonal shifts in photoperiod, the alligator is an excellent subject for 
the study of endogenous circadian clocks that are fine tuned by 
environmental cues (eg., light-dark, temperature variations). Whether 
there is one circadian clock or a number of subordinate circadian 
clocks each kept in synchronization with the others by natural 



36 



INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY 



0) 

en 



40 n 



30 - 



20- 



10 




Afternoon Evening Night Morning 



Figure 3. Transition of circadian predatory pattern from natural LD (solid triangles) 
to the first week (open circles) and fourth week (open triangles) of reversed LD. 



zeitgebers can only be determined by extensive research. Amphibious 
behavior, solar compass time compensation, photoreceptor sensitivity, 
motor activity, and predatory behavior all may be controlled by one 
"master" circadian clock, or each behavior may have its own 
independent circadian clock. Conversely, all of the above behaviors 
may reflect variations symptomatic of the animals' activity cycles. To 
resolve these issues, it would be necessary to measure continuously 
and concurrently all of these behaviors under controlled laboratory 
conditions. By manipulating light and temperature cues, it may be 
possible to produce desynchronization of the behaviors from each 
other thereby demonstrating subordinate circadian clocks for some or 
all of these behaviors. 



ACKNOWLEDGEMENTS 



Grateful acknowledgement is due to Ted Joanen and the 
Rockefeller Wildlife Refuge, Grand Chenier, LA for supplying the 
alligators for this research. Special acknowledgement is due to Dr 
Ethel Tobach, Dr Ernest G Maples and two anonymous reviewers for 
their valuable comments. 



JACK PALMER AND LINDA PALMER 37 

REFERENCES 

Aschoff, J. (1989). Temporal orientation: Circadian clocks in animals and humans. 

Animal Behavior, 37, 881-896. 
Binkley, S. (1979). A timekeeping enzyme in the pineal gland. Scientific American, 

240, 66-71. 
Coulson, R.A., & Hernandez, T. (1983). Alligator metabolism: Studies on chemical 

reactions in vivo. New York: Maxwell House. 
Galluscio, E.H. (1990). Biological psychology. New York: Macmillan Publishing 

Co. 
Gem, W.A., Owens, D.W., Ralph, C.L., & Roth, J.J. (1978). Plasma melatonin from 

extra-pineal sites. American Zoologist, 18, 557. 
Griffiths, R.A. (1986). Natural environmental cues and circadian rhythms of 

behaviour: A perspective. Chronobiology-Intemational, 3, 247-253. 
Kavaliers, M. (1980). Circadian rhythm of extraretinal photosensitivity in hatchling 

alligators, Alligator mississippiensis. Photochemistry and Photobiology, 32, 67- 

70. 
Kavaliers, M., & Ralph, C.L. (1980). Circadian organization of an animal lacking a 

pineal organ; the young alligator. Alligator mississippiensis. Journal of 

Comparative Physiology 139, 287-292. 
Kavaliers, M., & Ralph, C.L. (1981). Encephalic photoreceptor involvement in the 

entrainment and control of circadian activity of young American alligators. 

Physiology and Behavior, 26, 413-418. 
Lang, J.W. (1976). Amphibious behavior of Alligator mississippiensis: Roles of a 

circadian rhythm and light. Science, 191, 575-577. 
Mcllhenny, E.A. (1976). The alligator's life history. Society for the Study of 

Amphibians and Reptiles. (Original work published 1935). 
Murphy, P. (1981). Celestial compass orientation in juvenile American alligators 

{Alligator mississippiensis). Copeia, 3, 638-645. 
Pooley, A.C. (1989). Food and feeding habits. In C.A. Ross (Ed.), Crocodiles and 

alligators (pp. 76-91). New York: Facts on File, Inc. 
Ross, C.A., & Magnusson, W.E. (1989). Living crocodilians. In C.A. Ross (Ed.), 

Crocodiles and alligators (pp. 58-73). New York: Facts on File, Inc. 
Scott, T.P., & Weldon, P.J. (1990). Chemoreception in the feeding behavior of adult 

American alligators. Alligator mississippiensis. Animal Behavior, 39, 398-405. 
Weldon, P.J., Swenson, D.J.. Olson, J.K., & Brinkmeier, W.G. (1990). The American 

alligator detects food chemicals in aquatic and terrestrial environments. 

Ethology, 85, 191-198. 
Wurtman, R.J., & Lieberman, H. (1987). Melatonin secretion as a mediator of 

circadian variations in sleep and sleepiness. Integrative Psychiatry, 5, 13-14. 



International Journal of Comparative Psychology, Vol. 7, No. 1, 1994 



PORTIA LABIATA, A CANNIBALISTIC JUMPING 

SPIDER, DISCRIMINATES BETWEEN 

OWN AND FOREIGN EGGSACS 

Robert J. Clark 

Robert R. Jackson 

University of Canterbury 



ABSTRACT: Eggsac recognition was investigated in Portia labiata, a jumping spider 
(Salticidae) that routinely feeds on the eggs of conspecifics, but does not normally feed 
on its own eggs. In laboratory experiments, we demonstrate that P. labiata females can 
discriminate between their own and foreign eggsacs. The cues by which these 
discriminations are made are discussed. 



INTRODUCTION 

Various types of parental care are known in spiders, including 
guarding eggs against predators (Eberhard, 1974; Kessler & Fokkinga, 
1973; Pollard, 1984; Fink, 1986, 1987; Willey & Adler, 1989), providing 
food for young (N0rgaard, 1956; Bristowe, 1958; Kullmann, 1972; 
Shear, 1970) and opening the eggsac to allow emergence of spiderlings 
(Whitcomb & Eason, 1967). Generally, if a female that does not have 
eggs is offered eggs of a conspecific, she will reject, and sometimes eat, 
them (Bonnet, 1940; Palmgren, 1944; but see N0rgaard, 1956; Pollard, 
1984). Yet females do not normally eat their own eggs. 

In vertebrates, the stimuli by which females recognize their own 
offspring have been well studied (Fletcher & Michener, 1987), but the 
stimuli by which female spiders discriminate between their own eggs and 
those of conspecifics have received little attention. Previous studies 
suggest that eggsac discrimination by spiders is mediated by one or more 
of four cues (Kraft, 1982): (1) tactile cues based on the physical 



Address correspondence to Robert J. Clark, Department of Zoology, University of 
Canterbury, Christchurch, New Zealand. 

38 © 1994 International Society for Comparative Psychology 



ROBERT CLARK AND ROBERT JACKSON 39 

characteristics of the eggsac; (2) chemical cues associated with the 
eggsac's silk; (3) chemical cues associated with the spider's web; (4) cues 
based on the geographic location of the eggsac, the web or both. 

Portia is a web-building jumping spider that specializes in preying 
on other spiders, including conspecifics (Jackson, 1992). Portia females 
enter the webs of conspecifics, where they attack or sometimes kill the 
resident female, then eat any eggsacs that are left behind (Jackson & 
Blest, 1982; Jackson & Hallas, 1986). Upon encountering eggsacs, 
Portia females open them by chewing and tugging with their chelicerae, 
then using their front pair of legs to rake the eggs forward into their 
mouths (Jackson & Blest, 1982). 

Portia females have never been observed eating their own eggs. Yet 
females leave, then return to their webs during the incubation period 
(Jackson & Blest, 1982). Also, incubating Portia females in nature have 
been observed to eat eggs of conspecifics (Jackson & Blest, 1982; 
Jackson, unpubl. data). This suggests that P. labiata females have 
evolved an ability to recognize their own eggs or web. We investigated 
this hypothesis using a representative species, P. labiata, from Sri Lanka. 



MATERIALS AND METHODS 

Standard maintenance procedures were used, as described elsewhere 
(Jackson & Hallas, 1986). Tests were carried out in cages with 
removable glass sides (Fig lA). An internal metal frame was positioned 
inside each cage (Fig IB). Spiders attached their webs to the metal 
frame instead of to the glass, enabling the cages to be opened without 
damaging webs. 

All females used in tests were randomly selected from the laboratory 
stock. Though a given female was used in more than one (maximum of 
two tests) test, no eggsac-female pair was used more than once. Also, no 
eggsac was used more than once, except for instances in which it had 
previously been paired with its parent. All eggsacs used in tests were of 
approximately (maximum difference of 3 days) matching age. 

Before each test, the parent spider (test spiders and spiders that 
provided foreign eggsacs and webs) was deprived of contact with its 
eggsac and web for a 2-h period. After the 2-h period, the test female 
was placed in a cage containing one of the following treatments: (1) the 
test female's own eggsac in the test female's own web; (2) the eggsac 
and web of another conspecific female ('foreign eggsac in foreign web'); 
(3) the test female's eggsac in another conspecific female's web ('own 
eggsac in foreign web'); (4) the eggsac of another conspecific in the test 



40 



INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY 







B 



Figure 1. Cage (30 cm x 30 cm x 30 cm) used in testing Portia labiata for eggsac 
recognition. A: Wooden outer frame with sliding glass sides, one of which is shown 
partially raised. Prey were introduced through the four holes (plugged with corks) on top 
of the cage. B: Inner metal frame that is slightly smaller than the inside dimensions of 
outer cage. Inner frame is shown separately for clarity, but is normally positioned inside 
the outer wooden frame. 



female's web ('foreign eggsac in own web'). The test consisted of leaving 
the test female in the cage for one week, during which time the eggsac 
was checked daily for evidence of having been fed upon. 

Treatments 3 and 4 were obtained each time by taking a pair of 
incubating females' webs and trading the eggsacs: eggsac of female 1 
placed in web of female 2 as close as possible to previous location of 
eggsac of female 2, and likewise for eggsac of female 2 placed in web 
of female 1 . 



RESULTS 



Eggsacs encountered by test females in their own webs were treated 
differently depending on whether they belonged to the test female or 
another conspecific female (x^=47.62, N= 59): test females in their own 
webs resumed guarding their own eggsac in 19 out of 20 tests, and ate 
the foreign eggsac in only 6 out of 12 tests. 

Test females in foreign webs resumed guarding their own eggsacs 



ROBERT CLARK AND ROBERT JACKSON 41 

in 13 out of 14 tests and ate the eggsacs in 12 out of 13 tests. Eggsacs 
which the test female did not resume guarding were invariably eaten. 



DISCUSSION 

Evidently, P. labiata females can discriminate between their own 
eggsac and a foreign eggsac. In the present study, females usually 
guarded their own eggs and ate foreign eggs. How widespread eggsac 
recognition abilities may be in salticids is unknown because species 
other than P. labiata have not yet been studied. However, an ability to 
recognize their own eggs may be especially advantageous in Portia 
because this is a genus of salticids known to feed frequently on eggs of 
other spiders, including conspecifics. 

This study raises questions about the cues by which P. labiata 
distinguishes between its own and foreign eggsacs. In some vertebrates, 
cues from the geographic locations of the eggs are known to be 
important (Colgan, 1983). However, for P. labiata, cues other than 
location must be of primary importance. In our tests, when females' own 
eggsacs were placed in foreign webs, they were not placed in a location 
comparable to their original positions in the parent webs but, instead, as 
close as possible to the previous location of the foreign eggsac. 
Therefore, if the location of the eggsac in the web was the most 
important cue for eggsac recognition, then test females would have been 
expected often to eat their own eggsacs. However, test females usually 
guarded their own eggsacs, instead of eating them, regardless of whether 
they were in foreign webs or the females' own webs. Probably, in P. 
labiata, eggsac discrimination is based primarily on chemical cues. 

However, it is interesting that, when we placed foreign eggsacs in 
the webs of test females, the test females accepted (i.e., did not eat) the 
foreign eggsac half the time. Yet, when test females encountered foreign 
eggsacs in foreign webs, they usually ate them. This suggests that cues 
from the female's own web are important in addition to cues from her 
eggsac. It is probably unlikely in nature for a female to encounter 
foreign eggs in her own web and, therefore, it might be advantageous for 
females to be reluctant to eat eggsacs encountered in their own webs, 
despite dissenting chemical cues. 



42 INTERNATIONAL JOURNAL OF COMPARATIVE PSYCHOLOGY 

ACKNOWLEDGEMENTS 

We thank Andrew McLachlan, Mary Whitehouse and Philip Taylor 
for useful comments on the manuscript and Tracey Robinson for her 
invaluable help in the preparation of the manuscript. Financial support 
was provided by grants from the National Geographic Society (3226-85) 
and the U.S. -New Zealand Cooperative Program of the National Science 
Foundation (BNS 8657078). Import permits were provided by the New 
Zealand Ministry of Agriculture and Fisheries. 

REFERENCES 

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Bulletin Societe d'Histoire Naturelle Toulouse, 81, 185-250. 
Bristowe, W.S. (1958). The World of Spiders. London: Collins. 

Colgan, P. (1983). Comparative social recognition. New York: John Wiley & Sons. 
Eberhard, W.G. (1974). Maternal behaviour in a South American Lyssomanes. Bulletin 

of the British Arachnological Society, i, 51. 
Farley, C, & Shear, W.A. (1973). Observations on the courtship behaviour of Lycosa 

carolinensis. Bulletin of the British Arachnological Society, 2, 153-158. 
Fink, L.S. (1986). Costs and benefits of maternal behaviour in the green lynx spider 

{Oxyo^xdois., Puecitia viridans). Animal Behaviour, 34, 1051-1060. 
Fink, L.S. (1987). Green lynx spider egg sacs: source of mortality and the function of 

female guarding (Araneae, Oxyopidae). Journal of Arachnology, 15, 231-239. 
Fletcher, D.J.C., & Michener, CD. (1987). Kin recognition in animals. Chichester: John 

Wiley & Sons. 
Jackson, R.R. (1992). Eight-legged tricksters: spiders that specialize at catching other 

spiders. BioScience, 42, 590-598. 
Jackson, R.R., & Blest, A.D. (1982). The biology of Portia fimbriata, a web building 

jumping spider (Araneae, Salticidae) from Queensland: utilization of webs and 

predatory versatility. Journal of Zoology, 196, 255-292. 
Jackson, R.R., & Hallas S.E.A. (1986). Comparative biology of Portia africana, Portia 

albimana, Portia fimbriata, Portia labiata, Portia schultzi, araneophagic jumping 

spiders (Araneae, Salticidae): utilisation of webs, predatory versatility and 

intraspecific interactions. New Zealand Journal of Zoology, 13, 423-489. 
Kessler, A., & Fokkinga. A. (1973). Hymenopterous parasites in eggsacs of spiders of 

the genus Pardosa (Araneida, Lycosidae). Tijdschrift voor Entomologie, 116, 43- 

61. 
Kraft, B. (1982). The significance and complexity of communication in spiders. In P.N. 

Witt & J.S. Rovner (Eds.), Spider communication: mechanisms and ecological 

significance. Princeton: Princeton University Press. 
Kullman, E.J. (1972). Evolution of .social behavior in spiders (Araneae: Eresidae and 

Theriididae). American Zoologist, 12, 419-426. 
N0rgaard E. (1956). Environment and behavior ot'Theridion saxatile. Oikos, 7, 159-162. 
Palmgren, P. (1944). Uber die brutpfleginstincthandlung der wolfspinnen. Societas 

Scientiarum fennica-Commentationes Biologicae, 9, 1-19. 



ROBERT CLARK AND ROBERT JACKSON 43 

Pollard S.D. (1984). Egg guarding by Clubiona cambridgei (Araneae, Clubionidae) 

against conspecific predators. Journal of Arachnology, ]], 323-326. 
Shear W.A. (1970). The evolution of social phenomena in spiders. Bulletin of the British 

Arachnological Society, 1, 65-76. 
Whitcomb W.H., Eason R. (1967). Life history and predatory importance of the striped 

lynx spider (Araneida, Oxyopidae). Proceedings of the Arkansas Academy of 

Science, 21, 49-58. 
Willey, M.B., & Adler P.H. (1989). Biology of Peucitia viridans (Aranae, Oxyopidae) 

in South Carolina, with special reference to predation and maternal care. Journal 

of Arachnology, 17, 275-284. 



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