The effect of turtle locomotor style on plastron shape and strength

Meeting Abstract

P3.142  Monday, Jan. 6 15:30  The effect of turtle locomotor style on plastron shape and strength MUNTEANU, VD*; STAYTON, CT; Bucknell University; Bucknell University

The shells of aquatic and terrestrial turtles are well known to differ in shape. The most well-studied differences involve features of the carapace: terrestrial turtles tend to have tall, domed carapaces, while the carapaces of aquatic turtles are flatter. These differences in shape are known to have functional implications – the more domed carapaces of terrestrial taxa develop lower stresses for a given load than those of aquatic taxa. However, given the differences in locomotor styles, and the consequent differences in typical limb movements between aquatic and terrestrial taxa, differences in the shapes of the plastron are expected as well. These differences in plastron shape are likely to have important functional consequences. We investigated differences in the morphology and mechanical performance between the plastrons of aquatic and terrestrial emydid turtles. Given the differences in limb orientation and motion required by terrestrial locomotion relative to aquatic locomotion, we hypothesized that terrestrial turtle plastrons will be narrower than those of aquatic turtle plastrons and will have a larger bridge region. Given this, we also predicted that the plastrons of aquatic turtles will be stronger than the plastra of terrestrial turtles, but that the bridges of aquatic turtles will be weaker. We used geometric morphometrics methods to test our morphological hypotheses and finite element analysis (FEA) to test our functional hypotheses. We found support for our morphological hypotheses. However, we found that the plastra and bridges of terrestrial turtles were stronger, on average, than those of aquatic turtles. These results imply that differences in locomotor style do indeed affect plastron shape in aquatic and terrestrial species, but that there is not necessarily a trade-off between plastron strength and efficiency of terrestrial locomotion.

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