Thermal Characteristics of Shelter Rocks Used by Gravid Female Timber Rattlesnakes Crotalus horridus In the Appalachian Mountains of Northern Georgia
Thermal environments created by such retreats as shelter rocks can heavily influence both physiological and behavioral processes in ectotherms. For viviparous species, successful gestation of developing embryos demonstrates one critical physiological process for which suitable thermal retreats are often sought. Female Timber Rattlesnakes (Crotalus horridus),a viviparous species found throughout the Appalachian Mountains, rely on exposed rock outcroppings for gestation and birthing, using the same shelter rocks for both purposes. We investigated thermal characteristics of repeatedly used shelter rocks to determine if these sites represent unique thermal microhabitats. We chose six shelter rocks located in the mountains of northern Georgia and paired each with a nearby, seemingly suitable, unused rock as a control. We used data loggers to record temperature under each rock every 15 min across an entire active season. We randomly chose 50 data points for each rock for analyses. Because the data were normally distributed, we used a 2-way ANOVA, testing for differences among pairs and between treatments (used versus unused). There was no difference in treatments in mean temperature, although there were highly significant differences among pairs. The results of a test of equality of variance between the pooled gestation data and the pooled control data indicated a significantly higher variance among the control data, although this pattern was not present for all rock pairs. Active behavioral thermoregulation by rattlesnakes throughout each day may preclude the need for reliance on unique thermal microhabitats associated with shelter rocks.
Dept of Natural Sciences, Piedmont College, Demorest, GA
Assessment Behavior in Neonate Copperhead Snakes Is Correlated With Familiarity and Not Kinship
Reptiles have been traditionally viewed as asocial. However, recent evidence suggests that some squamate reptiles, notably pitviper snakes, may possess individual recognition capabilities, and in some cases aggregate in kin-based social groups. Such sociality requires individuals to recognize and remember one another over time. Here we describe a novel behavior in neonate copperhead snakes, Agkistrodon contortrix, that may function in individual recognition through chemoreception, the primary mode of communication in snakes. We tested whether the behavior (assessment) differs in duration and frequency between test groups composed of sibling and non-sibling pairs, either raised together or separately. Although the assessment behavior does not differ in duration when tested after six months of isolation, we found that naïve individuals perform the assessment behavior more frequently than do individuals having previous experience with one another. Our results suggest that recognition of individuals is correlated with interactions experienced during the first three weeks after birth and that those interactions can be recalled after six months.
Dept of Biology, Wofford College, Spartanburg, SC
P147 • Neil Choyce, Charles F. Smith
Reproductive Investment in Female Copperheads (Agkistrodon contortrix) at the Extreme of Their Northern Range: Do Large Females Produce Large Progeny?
Female investment in reproduction may entail trade-offs, i.e. energetic tradeoffs between current and future reproductive investment; neonate size versus neonate number and frequency of reproduction versus energy allocated at each reproductive event. Trades-offs may be more pronounced in ectotherms because their morphology, physiology, behavior, and reproduction are strongly tied to the environment, particularly in higher latitudes or elevations. While larger neonates have been shown to have better performance and higher survival rates, female viviparous snakes typically produce more neonates rather than larger neonates as female body size increases. We tested the hypothesis that increase in female body size results in the production of larger neonates, rather than more neonates, in northern populations of viviparous snakes (Viperidae: Agkistrodon contortrix) where ingress to hibernation occurs shortly after parturition (thus strong selection on neonate survival). Contrary to our hypothesis, an increase in female body size in A. contortrix does not result in larger neonates. Rather, larger females produce more neonates consistent with previous studies. Because thermal dependence of embryonic development is widespread among squamate reptiles, female copperhead snakes in northern latitudes may be constrained from producing larger neonates, (perhaps by extending gestation length), due to decreasing environmental temperatures in late summer months.
Dept of Biology, Wofford College, Spartanburg, SC
P148 • Callie C. Wolfe1, Tyler J. Fisk1, Sarah A. Smiley2, Terence M. Farrell1
The Effect of Prey Type on Foraging Behavior in Pigmy Rattlesnakes (Sistrurus miliarius)
Pigmy rattlesnakes are dietary generalists that consume amphibians, reptiles, mammals and centipedes. We investigated foraging in pigmy rattlesnakes in laboratory feeding trials using Ground Skinks (Scincella lateralis) and Florida Blue Centipedes (Hemiscolopendra marginata). We videotaped 15 field-collected snakes in 16 centipede and 15 skink trials. Rattlesnakes envenomated centipedes significantly more often than skinks and in 62.5% of trials centipedes were consumed, whereas, skinks were eaten in only 26.7% of trials. There was no statistically significant difference in mean time to first strike between prey species. However, there was a trend towards shorter mean strike distance in centipede trials. Venom acted more slowly in centipedes resulting in a significantly longer mean period between the strike and the prey’s last locomotion as well as a longer period between the strike and the initiation of ingestion of the prey. It also took snakes significantly more time to complete ingestion once it was started for centipedes than skinks. Unlike skinks, centipedes were frequently consumed while still alive and by the midbody region rather than head first. Head elevation was exhibited by rattlesnakes approaching centipede prey significantly more frequently than when approaching skinks. Many of the observed differences in foraging behavior appear to result from centipedes low susceptibility to rattlesnake venom and their potent retaliatory strikes. The behavioral plasticity exhibited by pigmy rattlsnakes in foraging may be crucial to their success as generalist predators.
1 Biology Dept, Stetson University, DeLand, FL; 2 Evolution, Ecology and Organismal Biology, Ohio State University, Columbus, OH
