Article

Serial homology and the evolution of mammalian limb covariation structure

Department of Cell Biology and Anatomy, University of Calgary, Health Sciences Centre, 3330 Hospital Drive NW, Calgary, Alberta T2N 4N1, Canada.
Evolution (Impact Factor: 4.66). 01/2006; 59(12):2691-704. DOI: 10.1554/05-233.1
Source: PubMed

ABSTRACT The tetrapod forelimb and hindlimb are serially homologous structures that share a broad range of developmental pathways responsible for their patterning and outgrowth. Covariation between limbs, which can introduce constraints on the production of variation, is related to the duplication of these developmental factors. Despite this constraint, there is remarkable diversity in limb morphology, with a variety of functional relationships between and within forelimb and hindlimb elements. Here we assess a hierarchical model of limb covariation structure based on shared developmental factors. We also test whether selection for morphologically divergent forelimbs or hindlimbs is associated with reduced covariation between limbs. Our sample includes primates, murines, a carnivoran, and a chiropteran that exhibit varying degrees of forelimb and hindlimb specialization, limb size divergence, and/or phylogenetic relatedness. We analyze the pattern and significance of between-limb morphological covariation with linear distance data collected using standard morphometric techniques and analyzed by matrix correlations, eigenanalysis, and partial correlations. Results support a common limb covariation structure across these taxa and reduced covariation between limbs in nonquadruped species. This result indicates that diversity in limb morphology has evolved without signficant modifications to a common covariation structure but that the higher degree of functional limb divergence in bats and, to some extent, gibbons is associated with weaker integration between limbs. This result supports the hypothesis that limb divergence, particularly selection for increased functional specialization, involves the reduction of developmental factors common to both limbs, thereby reducing covariation.

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    • "In addition, the radius and ulna must interact during pronation and supination movements , which are important during locomotion and other behaviours (such as grasping, digging, prey capture and grooming). Consequently, we predict that there will be a greater degree of shape co-variation and morphological Fig. 2 Schematic representation of the developmental expression of 5 0 Hox paralogous 9–13 involved in the proximodistal patterning of forelimb in mice (modified from Wellik & Capecchi, 2003; Young & Hallgr ımsson, 2005; Schmidt & Fischer, 2009; Young et al. 2010) showing in the first box the developmental modules: the blue box represents the humerus module and the yellow box represents the ulna and radius module; the second box represents functional modules involved in movements of rotation (green) and flexion–extension (red). Primary expression pattern is shown in black; lesser expression is shown in grey. "
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