BERDNIKOVS, Sergejs; University of Cincinnati: Evolution of sexual dimorphism in shape of the pelvic bones of Mustela (Carnivora, Mammalia)

The pelvic bones (os coxae) play a critical functional role in animal support, locomotion and parturition. One of the biggest controversies surrounding this structure concerns evolution of differences in pelvic shape between sexes. Two alternative evolutionary explanations of pelvic sexual shape dimorphism are (1) a correlated consequence of differences in size between sexes (allometry) and (2) direct selection pressure on shape, most likely due to internal gestation and parturition in females. The problem in testing these hypotheses lies in the difficulty of accurate description and quantification of shape differences of these anatomically complex bones. I applied a thin plate spline morphometric analysis (Bookstein, 1991) in a comparative phylogenetic framework to resolve the allometry-function controversy in one group of closely related mammals (the genus Mustela). This landmark-based geometric morphometric approach provides a precise description of pelvic shape and quantifies both global and localized shape changes, permitting testing of the relationship between size (pelvic centroid size) and pelvic shape sexual dimorphisms (partial warps of thin plate spline analysis). Significant differences in pelvic shape exist between sexes and among species. Localized expansion of pelvic inlet area in females supports the hypothesis that sexual dimorphism is the consequence of direct selective pressure on females in several Mustela species. Phylogenetic analysis of shape data pointed to the broad patterns of the evolution of sexual shape differences in the pelvic area as well as gave clues to their functional significance.