Meeting Abstract

102.6  Saturday, Jan. 7  Are the plastral scutes and plastral lobes of turtle shells modules? A geometric morphometric perspective ANGIELCZYK, K. D.*; MELSTROM, K. M.; Field Museum of Natural History; Univ. of Michigan

The turtle plastron (ventral shell) is covered by a series of keratinous scutes. Each scute is derived from one tissue condensation; therefore we might expect the scutes to be separate developmental modules. Similarly, the anterior and posterior plastral lobes of turtles with a hinged plastron may be separate modules because each lobe has to articulate with different parts of the carapace. To test these hypotheses, we used Klingenberg's application of the RV coefficient to geometric morphometric data to examine patterns of integration in the plastra of 884 specimens belonging to 12 emydid and kinosternid species. When the fluctuating asymmetry component of shape variation was considered, RV scores for configurations that were divided into modules representing individual scutes were consistently in the left tail of the distribution of possible RV scores. RV scores for configurations divided into modules representing the anterior and posterior lobes also were low, although some akinetic species had slightly higher scores. When the among-individuals component of shape variation was considered, RV scores for the emydid species were all near the high ends of their distributions when the configurations were divided into scutes, whereas the scores for kinosternids were low. RV scores for configurations divided into anterior and posterior lobes spanned a wide range, and there was not a consistent difference between kinetic and akinetic species. Together, these results are consistent with the individual scutes and the plastral lobes being independent developmental modules within individuals. However, the factors that affect shape variation among individuals seem to influence the plastron in a much more integrated way, at least for the species we sampled.