COLLAR, D.C.*; NEAR, T.J.; WAINWRIGHT, P.C.; University of California, Davis; University of Tennessee, Knoxville; University of California, Davis: Comparative studies of morphological diversity: trophic evolution in centrarchid fishes

Evolutionary lineages differ with respect to the variety of forms they exhibit. We investigated whether comparisons of morphological diversity can be used to inform about differences in ecological diversity in two sister clades of centrarchid fishes. Species in the Lepomis clade (sunfishes) feed on a wider range of prey items than species in the Micropterus clade (black basses). We quantified morphological variation in the trophic apparatus as within-clade variance on principal components and found that Lepomis exhibits 4.4 and 6.5 times more variance than Micropterus on the first two principal components. However, lineages are expected to diversify morphologically and ecologically given enough time, and this pattern could have arisen due to differences in the amount of time each clade has had to accumulate variance. Despite being sister groups, the age of the most recent common ancestor (MRCA) of Lepomis is 14.6 million years ago (mya) and its lineages have a total length of 85.6 million years (My) while the age of the MRCA of Micropterus is only 9.1 mya and it has a total branch length of 46.8 My. We used the Brownian motion model of character evolution to test the hypothesis that morphological variance accumulates at the same rate within each clade and determined that the rates of evolution of the first two principal components are 4.7 and 7.5 times greater in Lepomis. Thus, time and phylogeny do not account for the observed differences in morphological disparity, and other diversity-promoting mechanisms should be investigated. We suggest that rates of morphological evolution are time- and phylogeny-independent, and therefore provide an appropriate metric for comparing phenotypic diversity between any pair of clades.