YOUNG, Nathan M.; HALLGRIMSSON, Benedikt; University of Calgary; University of Calgary: A Comparison of Patterns of Forelimb and Hindlimb Covariation in Mammals

Within mammals there is remarkable structural diversity in limb morphology, with a variety of functional relationships between and within hind and forelimb elements. Improved understanding of the developmental genetic basis of fore- and hind limb identity indicates both limbs share a broad range of developmental pathways. Morphological integration theory predicts covariation between limb traits should be reduced in those lineages where selection for morphologically divergent forelimbs or hindlimbs has occurred. The evolution of specialized limbs should favor interlimb traits that are selectively orthogonal to each other, otherwise severe negative fitness consequences would entail. In this project we assess whether covariation between limbs is greater in mammalian taxa with structurally similar forelimbs and hindlimbs compared to those with structurally divergent limbs. We analyze the pattern and significance of interlimb morphological integration in morphometric data from a broad range of mammalian taxa (primates, carnivores, chiropterans, rodents) that exhibit varying degrees of fore- and hindlimb specialization or functional divergence. Data is collected from adult fore- and hindlimb elements (scapula, ilium, humerus, femur, radius, tibia, third metacarpal, and third metatarsal) using standard morphometric techniques. Linear distance measurement are subjected to an analysis of integration using randomization methods and principal components analysis. These data are also used to test whether taxa with structurally divergent limbs have weaker between limb covariation than those with less divergent limbs. Future studies are planned to build on this work by experimentally manipulating genes involved in developmental pathways that are either associated with one limb type or both, and then assess the effect on patterns of limb covariation.