Unable to Diversify

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Science  03 Jul 2009:
Vol. 325, Issue 5936, pp. 12
DOI: 10.1126/science.325_12a

The decline in fitness with increasing distance from an adaptive peak can constrain morphological divergence between sister lineages. Collar et al. examine whether the functional demands of feeding on fish have limited morphological diversification in the Centrarchidae, an endemic clade of North American freshwater teleosts that includes sunfish and bass. To reconstruct ancestral feeding strategies, they map diet data synthesized from the literature onto a well-resolved, time-calibrated, multilocus phylogeny of 29 extant species. After measuring functional aspects of the skull, they carried out principal-components analysis of seven size-corrected morphological variables and total length. For each principal component (PC), the authors compare the fit of several evolutionary models, allowing parameters to vary across lineages with different degrees of piscivory. Two adaptive peaks (piscivory and nonpiscivory) appear to have influenced the evolution of PC1, with strongest loadings on the pharyngeal jaw adductor muscle and lower jaw out-lever. Brownian motion models reveal slow evolution of PC2 (muscle closing oral jaws) and PC4 (gape width) in fish-eating lineages. These findings indicate that piscivory has curtailed the diversification of feeding morphology in the centrarchids and that the effects have been strongest in highly piscivorous lineages.

Evolution 63, 1557 (2009).

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