BERDNIKOVS, Sergejs; University of Cincinnati: Sexual Dimorphism and Morphological Integration in Mustelid Pelvis

Morphological integration, the evolutionary pattern of trait correlation due to commonality in function within a form, is an important consideration in the pelvis, which consists of several different bones, and serves several different functions. Understanding the evolution of the pelvis is complicated by these functions, one of which, parturition, differs between the sexes. I tested two evolutionary hypotheses concerning pelvic sexual dimorphism in extant taxa: (1) direct selection pressure on shape due to parturition in females or (2) a correlated consequence of differences in size between sexes, allometry. The carnivore family Mustelidae is excellent model for examining pelvic evolution, as there are many species, a resolved phylogeny, and significant variation in body size and sexual dimorphism. I first analyzed shape and morphological integration patterns in the pelvis of both sexes of seventeen mustelid species using landmark-based geometric morphometrics methodology and resampling-based matrix correlation techniques. I used these data on the covariation patterns in this structure to examine the hypotheses about sexual dimorphism. Significant differences in pelvic shape and degree of integration exist between sexes and among species. Sexual dimorphism in the pelvic shape was found to be largely the consequence of parturition function as supported by localized expansion and higher degree of covariation in the pelvic inlet area of females in most mustelid species. In addition, sexual shape dimorphism in the pelvis was significantly correlated with relative neonatal size and did not correspond to the evolution of sexual size differences between sexes. These results suggest that the evolution of sexual dimorphism shows complex patterns that are the result of specific selective forces in a clade.