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Inter- and Intra-Specific Correlates of Habitat and Locomotion in Snakes


It is often thought that locomotion is the behavior that most shapes organismal form and

function. Among tetrapods, differences in locomotor ability both within and among

species are often thought to be the result of variation in the limbs and other aspects of the

appendicular skeleton. Snakes are both elongate and completely without limbs. While

this bauplan has served snakes well, it is nevertheless subject to constraint at several

levels--particularly with reference to friction and the effects of gravity. Several

functional hypotheses have been put forth attempting to relate variation in snake anatomy

and physiology with movement through particular types of habitat, but none have been

conducted in a strict, phylogenetic context.

This dissertation will address several of these hypotheses in an evolutionary

context to ask whether variation in snake anatomy and physiology is determined by

adaptive mechanisms, or is a consequence of phylogenetic history. I also examine

variation in locomotor performance in the corn snake, Pantherophis guttata.

I first address a long-standing hypothesis that the heart position in arboreal snakes

is an adaptive feature related to head up postures during climbing. I use a

phylogenetically diverse sample of snakes from several habitats to address the source of

the variation in heart position. We found a trend opposite previous studies and found that

phylogenetic effects were equally important as ecological effects. I also present a

response to criticism of this study in chapter two.

I then use a similar approach to that of chapter one to address whether variation in

the musculature in snakes is associated with adaptations to particular habitats. I use an

information-theoretic approach to develop and compare models that incorporate

morphological, behavioral, ecological and phylogenetic variables. I found evidence that a

model containing all variables best fit my data.

Finally, I examined whether there was variation in locomotor performance in the

corn snake, Pantherophis guttata. Having found variation in several measures of

performance, we found that variation in several novel, lower-level traits predicted

locomotor performance.

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