Functional performance of turtle humerus shape across an ecological adaptive landscape

Area of Science:

• Evolutionary biology
• Biomechanics
• Paleontology

Background:

• Adaptive landscapes visualize evolutionary selection and adaptation.
• Morpho-functional data analysis is increasingly important in evolutionary studies.
• Humerus morphology varies among turtles with different locomotor adaptations.

Purpose of the Study:

• To construct adaptive landscapes for turtle humerus morphology.
• To explore functional trade-offs in marine, semiaquatic, and terrestrial turtles.
• To link form, function, and ecological adaptation in turtles.

Main Methods:

• Quantified humerus shape in 40 cryptodire turtle species using pseudolandmarks.
• Measured four functional traits (strength, stride length, mechanical advantage, hydrodynamics) on hypothetical shapes.
• Employed quantitative trait modeling to build adaptive landscapes optimizing traits for each ecology.

Main Results:

• Turtles in different environments exhibit statistically significant differences in humerus shape.
• Optimal adaptive landscapes vary across ecologies, with species grouping around specific adaptive peaks.
• Species follow Pareto fronts between marine-semiaquatic and semiaquatic-terrestrial optima, but not marine-terrestrial.

Conclusions:

• Adaptive landscapes are useful for understanding the form-function-ecology link.
• A framework is established for reconstructing turtle evolution from fossil humeri.
• Humerus shape variation reflects adaptation to diverse locomotor environments.