ALFARO, M/E; WAINWRIGHT, P/C; Univ. of California, Davis: A simulation study of the relationship between morphological and functional diversity in fish jaws

It is widely thought that ecological diversity is strongly correlated with morphological diversity although this assumption, which underlies many comparative evolutionary studies, has rarely been examined. We tested this hypothesis by simulating the evolution of four-bar mechanisms in labrid fishes. The four-bar is a simple mechanism with one degree of freedom. Thus the functional properties of the system for a given amount of input rotation are determined exactly by the lengths of the four elements. Because morphology and function are both simple to quantify, the four bar mechanism provides a model system for examining the relationship between morphological and functional evolution in complex traits. We evolved the elements of the four bar mechanism under a Brownian model of character change on 500 taxon trees and recorded morphology and lever mechanics (expressed as the ratio between rotation of the output and input links, kinematic transmission coefficient or KT) in the terminals. We then characterized diversity in morphology as the summed variance in lengths of the four-bar elements and functional diversity as the variance in KT for the entire tree and calculated the correlation between these parameters from 500 replicates of the simulation. We found no relationship between morphological and functional variance, suggesting that morphological diversity may be a poor predictor of functional and ecological diversity in even relatively simple systems.