Functional Tradeoffs in Specialization for Locomotion Versus Fighting

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Both rapid, economical running and fighting are important in the life histories of most or all terrestrial species. Nevertheless, musculoskeletal "design" that allows rapid, economical running is likely to be incompatible with musculoskeletal design that is appropriate for fighting. This locomotor versus fighting tradeoff may explain many cases of divergence in body form among closely related species and may also help explain why males and females of the same species often differ in the size and proportions of their musculoskeletal system. This study will use comparative methods to test hypotheses of functional tradeoff between specialization for rapid, economical running versus specialization for fighting. The first aim of the investigation is to test a broad set of hypotheses of functional design of the skeletal system in two mammalian orders: Artiodactyla (e.g., deer and antelope) and Carnivora (e.g. wolves and lions). Using museum collections, limb bone proportions will be measured in a large number of species and compared with proxies for male-male aggression (size sexual dimorphism) and maximum running speed. The second and third aims of the study are to quantify sexual differences in the properties of limb bones and muscle architecture in 2 species exhibiting high levels of male-male competition (black bears and bisons) and 2 highly cursorial species (wolves and pronghorns). Hence, this investigation will test hypotheses of functional tradeoff between musculoskeletal specializations for running versus fighting and it will significantly expand our knowledge and understanding of the sexual dimorphism of the mammalian musculoskeletal system. The study will also provide research opportunities for 6 to 9 undergraduate students. We will also create an open access, online library of high resolution CT scans of anatomically aligned cross-sections of the whole limb bones from all of the subjects. Finally, although sexual dimorphism is poorly understood by the general public, it is of broad importance to physiology, evolutionary biology, and human evolution and behavior. We expect the research proposed here to be of general interest and to provide opportunities to educate the public about the biological significance of sexual dimorphism.