Meeting Abstract

15.1  Thursday, Jan. 3  Can Modular Variation Affect Patterns of Morphological Disparity in the Rodent Mandible? MARQUEZ, E.J.; UNIV. OF MICHIGAN, ANN ARBOR emarquez@umich.edu

The relationship between modularity and disparity of mandible shape was studied in 11 species of oryzomyine rodents, using geometric morphometrics. A novel approach in which explicit expectations from hypotheses of modularity are tested against morphometric data was used to delimit modules in those species. Most modules appear to be evolutionarily labile, suggesting that some modules, corresponding to highly integrated regions, are found in diverse combinations in different species. Two conservative, highly integrated modules are identified, comprising (1) the coronoid and angular and, to a lesser extent, condylar processes, and (2) molar and incisor alveoli, including the portion of the incisor alveolus within the ascending ramus. To investigate whether overall evolutionary divergence has accumulated in a correlated manner within these modules, disparity was measured and decomposed to obtain estimates of the relative contribution of each region to the distinctiveness of each sampled species. Comparing these estimates across mandible regions resulted in moderate positive correlations only between coronoid and angular processes, and molar and incisor alveoli, partially agreeing with the modules found in previous tests, but inconsistent with species-specific covariation patterns. Analyses thus do not support a relationship between intraspecific patterns of integration and interspecific patterns of correlated divergence among mandible regions, suggesting instead the intriguing possibility that only traits forming conserved associations tend to show similar rates or magnitudes of divergence. These conservative modules may thus influence the dynamics of correlated evolution within the mandible complex.