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Dryad

Shell shape does not accurately predict self-righting ability in hatchling freshwater turtles

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Apr 23, 2024 version files 5.56 MB

Abstract

The different degrees of hydrodynamic shell shape in freshwater turtles likely represent an evolutionary trade-off between adaptation to an aquatic lifestyle and the movement capabilities of a larger and more rounded shell. Trade-offs often result in compromises, and this is particularly true when these turtles must self-right to avoid the negative effects of inverting. With flatter carapaces aquatic turtles, theoretically, must invest more biomechanical effort than their terrestrial counterparts with their more rounded carapaces, to achieve successful and timely self-righting. This places the hatchlings of freshwater species in a precarious position; more prone to inversion and predation than adults and with shells seemingly maladapted to the act of self-righting. Here, we examine the self-righting performance in three morphologically distinct freshwater turtle species (Apalone spinifera, Chelydra serpentina and Trachemys scripta scripta) that inhabit similar environmental niches. We demonstrate that hatchlings of these species were capable of rapid self-righting and used considerably less biomechanical effort relative to adult turtles. Despite differences in shell morphology the energetic efficiency of self-righting remained remarkably low and uniform between the three species of freshwater hatchling. Our results confound theoretical predictions of self-righting ability based solely on shell shape metrics and indicate that other morphological characteristics like neck or tail morphology and shell material properties must be considered to better understand the biomechanical nuances of Testudine self-righting.