Meeting Abstract

2.1  Thursday, Jan. 3  Ecological divergence in sympatric populations of the Gold-breast Splitfin, Ilyodon furcidens HUIZINGA, M.*; GHALAMBOR, C.K.; Colorado State University; Colorado State University Meribeth.Huizinga@ColoState.edu

Understanding the processes that generate and maintain patterns of diversity both within and between species is a central focus of evolutionary ecology. The combined effects of natural and sexual selection are thought to give rise to and maintain variation within populations primarily by driving polymorphisms via individual specialization, which can lead to sympatric divergence and eventually ecological speciation. Specialization in resource use has resulted in a variety of conspicuous polymorphisms where sympatric individuals exhibit altered morphology, life history and behavior. Yet, while several studies have demonstrated the presence of coexisting ecological morphs, few have successfully established a link between intraspecific morphological variation and fitness. Here we test the role of selection in generating and maintaining variation, by comparing geographically isolated populations of the livebearing fish, Ilyodon furcidens. We describe differences in trophic morphology, diet, and mating patterns both within and among the sample populations. Our results show that populations of I. furcidens exhibit either a unimodal or bimodal frequency distribution of relative mouth width and that individuals of bimodal populations show significant differences in a suite of trophic characteristics and the degree of diet specialization. We relate this morphological variation to fitness estimates, and these results are discussed in the context of maintenance of morphological variation through selection and assortative mating, with implications for frequency-dependent selection.