Meeting Abstract
Evolutionary biologists have considered understanding the relationship between organismal morphology and functional performance to be fundamental for understanding phenotypic diversification. Numerous studies have investigated performance and morphological evolution within lineages. However, far less attention has been paid to the relationship between performance and morphological diversification among lineages. This study develops the turtle shell as a model system for studying morphological and performance diversification in a comparative context. In particular, this study focused on differences between aquatic and terrestrial turtle species. Original data consisted of 3D landmark coordinates of 1962 turtle shells representing 254 separate species. Turtle shell performance was assessed for numerous functions through finite element modelling of strength and the computation of various shell shape indices. Phylogenetic MANOVA or ANOVA was used to test for differences in shell shape and performance between aquatic and terrestrial turtle species. In general, shape showed strong phylogenetic signal throughout the turtle phylogeny. Similarly, performance measures also showed strong phylogenetic signal. Significant differences in performance, but not morphology, were found between aquatic and terrestrial shells. The shells of terrestrial turtles, though not all the same shape, are stronger, easier to overturn, produce more drag, and exchange heat more slowly, than those of aquatic species. This combination of functional distinctiveness without morphological distinctiveness suggested the operation of many-to-one mapping of shell form onto function, which was investigated in Part II of this study.
