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Alligator appendicular architecture across an ontogenetic niche shift
Brandon P Hedrick1, Emma R Schachner1, Peter Dodson2,3
1Department of Cell Biology and Anatomy, School of Medicine, Louisiana State University Health Science Center, New Orleans, Louisiana.
Anatomical Record (Hoboken, N.J. : 2007)
|July 26, 2021
Summary
American alligators (Alligator mississippiensis) show continuous limb shape changes with size, not punctuated shifts. Adult alligators exhibit greater limb shape disparity, but the niche shift doesn't impact limb morphology.
Area of Science:
- Evolutionary biology
- Comparative anatomy
- Herpetology
Background:
- Species often shift ecological niches during development (ontogeny).
- These ontogenetic niche shifts can influence morphology, particularly limb structure, due to differing environmental demands.
- The American alligator (Alligator mississippiensis) undergoes significant habitat and dietary shifts during its development.
Purpose of the Study:
- To investigate if ontogenetic niche shifts and sexual maturity in American alligators correlate with punctuated changes in limb bone morphology.
- To analyze limb shape trends, shape disparity, and integration across different developmental stages.
Main Methods:
- Geometric morphometrics applied to scapulae, humeri, ilia, and femora of American alligators.
- Analysis of limb shape, shape disparity, and integration in relation to size and developmental stage (juvenile, subadult, adult).
Main Results:
- Limb shape strongly correlated with size, showing a continuous gradient rather than abrupt changes.
- Adult alligators (>1.8 m) displayed significantly higher limb shape disparity compared to younger individuals.
- Forelimbs and hindlimbs functioned as a single integrated unit, with no significant difference in integration between them.
Conclusions:
- The ontogenetic niche shift in American alligators does not directly cause punctuated changes in limb morphology.
- Increased limb shape disparity in adults may be linked to reduced limb use and relaxed developmental constraints.
- Limb shape evolution in this species appears to be driven by continuous size-related factors rather than discrete developmental transitions.
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