78.3 Friday, Jan. 6 Ecological opportunity and competition predict widespread disruptive selection in the wild MARTIN, R.A.*; PFENNIG, D.W.; Univ. of North Carolina, Chapel Hill; Univ. of North Carolina, Chapel Hill email@example.com
Disruptive selection occurs in a population when two or more modal phenotypes have higher fitness than the intermediate phenotypes between them. Such selection has long been viewed as being important in maintaining and increasing variation within natural populations; in favoring the evolution of alternative phenotypes; and initiating speciation. Nevertheless, disruptive selection has traditionally received relatively little attention. As a consequence, few studies have looked for evidence of disruptive selection in natural populations and relatively little is known regarding its underlying causes, its prevalence in natural populations, or the ecological factors that may promote it. We address these issues in natural populations of Mexican spadefoot toad tadpoles (Spea multiplicata), which are highly variable in trophic morphology and resource use. First, using an experimental approach, we show that functional tradeoffs among different trophic phenotypes for their preferred resources allow for frequency dependent competition, and that this competition generates disruptive selection. Next, to evaluate the prevalence and predictability of disruptive selection, we surveyed 15 ephemeral ponds containing S. multiplicata. We found that disruptive selection was the predominant mode of quadratic selection acting on resource-use phenotypes in these ponds. Furthermore, disruptive selection was strongest in populations with high conspecific density and intermediate levels of ecological opportunity and phenotypic variation. Generally, these results suggest that disruptive selection can be common in natural populations and predictable in the presence of certain ecological conditions.