Doctoral Dissertation Research: Evolutionary and developmental influences on skeletal maturation and internal structure

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The shape of the skeleton for a given species reflects both developmental genetic processes dictated by genes and environmental influences resulting from life history. In studies of primates and humans, understanding the relative contributions of these processes can help in making inferences about behavior and relatedness among both living and extinct species. For example, in humans, the enlarged calcaneus, or heel bone, with its expanded trabecular (spongy) bone volume is a well-known adaptation associated with walking upright. In contrast, the dramatic reduction of the pisiform bone in the in human wrist compared to other primates is not well appreciated. The fact that these are the only bones of the wrist and ankle to form growth plates suggests that they are under similar developmental control despite their different functional demands in humans. As such these bones form an ideal model to determine differential effects of genetic patterning and life history on skeletal shape. Increased knowledge of how differences in skeletal growth affect bone shape may also improve our understanding of the etiology of skeletal disease. This work will be used to train a female graduate student and several undergraduates, and will also be the basis of several K-12 student and educator outreach programs throughout central Pennsylvania. Functional morphological studies of the calcaneus, and specifically its trabecular bone structure, are abundant given its critical role in the unique forms of locomotion observed in hominoids, but little is known about how development influences trabecular structure. This study will investigate how trabecular structure changes when growth is altered by mutations in developmental genes. A comparative study of pisiform and calcaneus ossification across anthropoid primates and a mouse outgroup will be used to assess degree of developmental integration between the fore and hind limbs. Developmental effects of growth plate structure on trabecular bone will be studied using CT scans of calcanei from mice with normal growth plates and Hox11 loss-of-function mice with known growth plate abnormalities.