The developmental basis of evolutionary changes in limb proportions
Mammalian limbs are complex morphological structures that exhibit an astonishing amount of diversity. This diversity is driven by changes in the relative proportions of the three limb segments that are conserved among mammals. Despite the importance of limb proportions to mammalian evolution, the developmental mechanisms that regulate mammalian limb proportions remain largely unknown. In this study, I address three questions whose answers will provide insights into the mechanisms through which mammalian segment proportion is determined: when and how does the forelimb achieve its adult proportions, when and how does the hind limb achieve its adult proportions, and when and how does the proportions of the fore-and hind limb diverge. I address these questions using mouse, the model mammalian species. Results of this study indicate that adult forelimb segment proportions are achieved through differing rates of segment growth after their initial condensation, adult hind limb segment proportions are achieved through differing rates of growth after their initial condensations, and fore- and hind limb proportions diverge by the time of the initial cartilage condensation of segments. These findings suggest that the proportions of mammalian limb segments are not established until well after their cartilage condensation, and sets up future research on the specific cellular and molecular mechanisms driving proportion differences among species.
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign