71.6 Jan. 7 How to be a miniature turtle: comparisons of ontogeny in the Emydinae using geometric morphometrics ANGIELCZYK, Kenneth; Univ. of Bristol firstname.lastname@example.org
Miniaturization is a widespread phenomenon among animals, and often is accompanied by profound changes in morphology, physiology, and development. An obvious question to ask about miniaturized species is how their ontogenies compare to those of their larger relatives. For example, do miniaturized species resemble tiny adults of larger species, or do they retain the size and morphology of juveniles of larger species? The Emydinae include two of the smallest extant turtle species, Glyptemys muhlenbergii and Clemmys guttata, as well as more normally-sized species. To examine whether these two species attained their small sizes by modifying their ontogenies, I compared ontogenetic changes in plastron shape in C. guttata, G. muhlenbergii, and their larger relatives using geometric morphometrics. The results of these analyses indicate that the ontogenies of C. guttata and G. muhlenbergii are not simply truncated versions of those of larger emydines. Instead, both species display unique alterations in plastron shape as they grow. The plastron shapes of C. guttata and G. muhlenbergii also tend to become more similar to those of their larger relatives as ontogeny progresses. The turtles examined in this study range from hatchlings to large adults, but no pre-hatching embryos were used. When combined with the morphometric results, this fact suggests that the major differences in plastron shape between the miniaturized emydines and their relatives form early in development, with post-hatching ontogeny counterbalancing these differences to some degree. This convergence between adult shapes may reflect constraints on the morphology of the shell imposed by its protective function or the need to maintain a relatively hydrodynamic shape in species that are amphibious or aquatic.