EVOLUTION OF SEXUAL DIMORPHISM IN MUSTELIDS

The existence of striking sexual dimorphism in morphology, such as extreme differences in body size and mass between males and females across various animal taxa, has inspired a wealth of research. However, the narrow focus on specific aspects of dimorphic variation in adults and lack of integration between various sources of information leaves many unresolved questions in sexual dimorphism evolution. I have studied dimorphism at different levels of organization in model mammalian species (mustelid carnivores and laboratory rat), with a focus on the least understood aspects of morphological evolution: 1) phylogenetic relationship between sexual size dimorphism and body mass in mustelids, 2) ontogenetic origins of adult sexual size and shape dimorphism in the growing pelvic skeleton, 3) evolution of sex differences in shape and phenotypic covariation in the adult pelvic skeleton, 4) developmental origin and intraspecific and interspecific divergence and maintenance of patterns of trait relationships in the skull. Collectively, results emphasize the evolution of sexual dimorphism as a product of evolutionary changes in both males and females. Greater rates of male body size evolution relative to females, coupled with a more rapid body size evolution in some taxa, produced correlated evolution of body size and sexual dimorphism. Sexual divergence in ontogenetic trajectories of bone remodeling of the pelvis was tied to hormonal events occurring at puberty and was related to reproductive function of female pelvis, ultimately leading to specific expression of shape dimorphism in adults. Evolutionary divergence of shape of the pelvis in adult males and females was also found to be the result of reproduction-related variation (females had more spacious birth canal reflecting demands of increasing neonatal size in more dimorphic species), as well as sexual differences in bone size (bones were more robust in males having larger muscle site attachments). Both the pelvis and the skull showed sexual dimorphism in details of trait relationships at both intraand interspecific levels, possibly related to integration differences in early and late development. The research of mechanisms producing developmental variation leading to differential expression of adult morphology in males and females may hold a key to understanding sexual dimorphism evolution. Acknowledgements There are many people, without whom, this research would not be possible. First, I would like to thank my research advisor, Dr. Rebecca German, who has been a wonderful and understanding mentor, and who introduced me both to life in America and life in graduate school. I also would like to thank my committee members, Drs. Bruce Jayne, Michal Polak, Ron DeBry, Robert Skipper and Tom Kane, who paid critical attention and helped to determine the course of my research. I owe many thanks to Drs. Miriam Zelditch, Don Swiderski, David Sheets, Jim Rohlf, Chris Klingenberg and Robert Young for introducing me to the complex world of geometric morphometrics and valuable research discussions. I specially thank Dr. Benedikt Hallgrimsson for countless hours spent together in discussions of research and data collection. I thank the curators of following museums who were extremely helpful while on data collection trips: Thor Holmes (University of Kansas Museum of Natural History), Bill Stanley (Field Museum of Natural History), Mark Omura and Judith Chupasko (Harvard Museum of Comparative Zoology), Jean Spence (American Museum of Natural History) and David Schmidt and Linda Gordon (National Museum of Natural History). In the past few years I have had many friends who have been my colleagues and also great people to spend time with outside the lab: Tim Reichling, Andy Lammers, Meredith Farmer, Shannon Niehaus, Melissa Maynard, Tim Higham, Lisa Day, Angela Horner, Nicole Yarbourgh, Shannon Hunt, Tom Mast, Adam Biales, Donna Carlson Jones and Marica Bernstein. Finally, I would like to thank my parents, Dzintra Berdnikova and Sergejs Berdnikovs, and my wife, Hiam Abdala-Valencia, for their infinite love and support.