Inter- and Intra-Specific Correlates of Habitat and Locomotion in Snakes
- Author(s): Gartner, Gabriel Emil Asher
- Advisor(s): Garland Jr., Theodore
- et al.
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