Abstract
To assess how ecological and morphological disparity is interrelated in the adaptive radiation of Antarctic notothenioid fish we used patterns of opercle bone evolution as a model to quantify shape disparity, phylogenetic patterns of shape evolution, and ecological correlates in the form of stable isotope values. Using a sample of 25 species including representatives from four major notothenioid clades, we show that opercle shape disparity is higher in the modern fauna than would be expected under the neutral evolution Brownian motion model. Phylogenetic comparative methods indicate that opercle shape data best fit a model of directional selection (Ornstein–Uhlenbeck) and are least supported by the “early burst” model of adaptive radiation. The main evolutionary axis of opercle shape change reflects movement from a broad and more symmetrically tapered opercle to one that narrows along the distal margin, but with only slight shape change on the proximal margin. We find a trend in opercle shape change along the benthic–pelagic axis, underlining the importance of this axis for diversification in the notothenioid radiation. A major impetus for the study of adaptive radiations is to uncover generalized patterns among different groups, and the evolutionary patterns in opercle shape among notothenioids are similar to those found among other adaptive radiations (three-spined sticklebacks) promoting the utility of this approach for assessing ecomorphological interactions on a broad scale.
Highlights
Morphological disparity, a measure of the variability in morphological form, is well recognized to be unequally distributed across vertebrate phylogeny (e.g., Erwin 2007; Pigliucci 2008; Sidlauskas 2008)
To assess how ecological and morphological disparity is interrelated in the adaptive radiation of Antarctic notothenioid fish we used patterns of opercle bone evolution as a model to quantify shape disparity, phylogenetic patterns of shape evolution, and ecological correlates in the form of stable isotope values
Using a sample of 25 species including representatives from four major notothenioid clades, we show that opercle shape disparity is higher in the modern fauna than would be expected under the neutral evolution Brownian motion model
Summary
Morphological disparity, a measure of the variability in morphological form, is well recognized to be unequally distributed across vertebrate phylogeny (e.g., Erwin 2007; Pigliucci 2008; Sidlauskas 2008). Understanding why phenotypic spaces possess these properties, and the evolutionary processes underlying their patterning, has long captured the attention of evolutionary biologists (e.g., Wright 1932; Simpson 1953; Gould 1989; Carroll 2005). In this regard, the study of adaptive radiations, groups that have rapidly diversified from a common ancestor to occupy a wide variety of ecological niches, has been of particular interest because these bursts a 2013 The Authors.
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