Serial homology and the evolution of mammalian limb covariation structure. Evolution, 59(12), 2691-2704

Department of Cell Biology and Anatomy, University of Calgary, Health Sciences Centre, 3330 Hospital Drive NW, Calgary, Alberta T2N 4N1, Canada.
Evolution (Impact Factor: 4.61). 01/2006; 59(12):2691-704. DOI: 10.1554/05-233.1
Source: PubMed


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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    • "Among these, suspicion of possible correlated evolution between each of the semicircular canals was indicated by the repetitive pattern represented by these structures. Serial homology can nowadays be understood as a type of intraorganismal homology, with repetitive features sharing a large proportion of their genetic architecture and developmental pathways (Harris et al. 2003; Young and Hallgrímsson 2005; Gómez-Robles and Polly 2012). According to this definition, the semicircular canals may well be serial homologues as they share a large part of their genetic and developmental pattern (Bok et al. 2007; Chang et al. 2008; Rakowiecki and Epstein 2013). "
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    • "There is an ongoing debate about the roles played by functional and developmental factors and their interactions in influencing morphological variation (Klingenberg , 2005; Hallgr ımsson et al., 2009; Klingenberg et al., 2010). One viewpoint is that genetic modularity should evolve to match developmental and functional modularity (Reidl, 1978; Cheverud, 1982, 1984; Wagner, 1996), whereas more recent studies highlight development as the source of all phenotypic variation (Nemeschal, 1999; Young and Hallgr ımsson, 2005; Zelditch and Swiderski, 2011). According to the latter viewpoint, for genetic (or phenotypic) modularity to match functional modularity, developmental interactions must evolve to match functional interactions. "
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