ANGIELCZYK, K.D.*; ROOPNARINE, P.D.; California Academy of Sciences; California Academy of Sciences: Morphological integration and modularity in the plastron of Emys marmorata (Testudines, Emydidae)

Several recent studies have used geometric morphometrics to examine morphological integration and modularity, but in most cases the methods used required the potentially interacting modules to be defined a priori. Here we present a rigorous method for identifying groups of landmarks that form integrated modules, and apply it to a data set consisting of 409 plastra of the turtle Emys marmorata. Landmark data sets were first scaled to unit centroid size and specimens aligned using Procrustean landmark alignment. Morphological integration was represented by the partial correlation between landmarks. These correlations were measured by considering each landmark to be a bivariate distribution of x and y coordinates, and subsequently calculating the partial correlation between pairs of landmarks, while holding other landmarks constant, using a multivariate matrix regression technique. We then divided our turtles into six centroid size classes which we analyzed independently. Bilaterally symmetric landmarks were highly correlated in all size classes. In addition, two modules, one comprising several anterior landmarks and the other several posterior landmarks, were evident in most cases. Correlations between landmarks in these modules tended to be strongest in larger specimens. The total number of significant correlations between landmarks also increased with size, suggesting that the plastron as a whole tends to become more integrated over ontogeny. This technique views morphological integration as a network of correlated landmarks, and will permit rigorous identification of morphological modules.