Integration and Evolvability in Primate Hands and Feet |
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Authors: | Campbell Rolian |
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Institution: | (1) Department of Cell Biology and Anatomy, University of Calgary, G503 - 3330 Hospital Drive NW, Calgary, AB, T2N4N1, Canada |
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Abstract: | Morphological integration theory predicts that sets of phenotypic traits that covary strongly due to developmental and/or
functional connections between them eventually co-evolve because of a coordinated response to selection, and accordingly become
less independently evolvable. This process is not irreversible, however, and phenotypic traits can become less integrated,
and hence more independently evolvable, in the context of selection for divergent functions and morphologies. This study examines
the reciprocal relationship between shared function, integration and evolvability by comparing integration patterns among
serially homologous skeletal elements in the hands and feet of a functionally diverse sample of catarrhine primates. Two hypotheses
are tested: (1) species in which the autopods are functionally more similar (e.g. quadrupedal monkeys) have more strongly
integrated autopods than species in which the autopods are functionally divergent (e.g. gibbons, humans) and (2) the latter
have autopods that are more evolvable, collectively and independently. Morphometric data from selected hand and foot digital
rays were used to derive phenotypic variance/covariance matrices. The strength of integration among autopods was quantified
using eigenanalysis and a measure of trait variational autonomy. Evolvability was estimated by subjecting phenotypic variance/covariance
matrices to simulated random selection gradients, and comparing evolutionary responses among species. Results indicate that
integration decreases as hands and feet become functionally divergent, and that the strongly integrated hand and foot skeletons
of quadrupedal monkeys respond to selection in a highly collinear manner, even when simulated selective pressures acting on
each autopod are in opposite directions in phenotypic space. Results confirm that the evolvability of morphological traits
depends largely on how strongly they covary with other traits, but also with body size. The role of pleiotropy as a developmental
mechanism underlying integration and evolvability is also discussed. |
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Keywords: | Morphological integration Evolvability Autopods Primates Pleiotropy |
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