Competition and the Origins of Diversity: An Empirical Test of the Ecological Speciation Hypothesis

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Ecological mechanisms that lead to speciation (the evolutionary splitting of one species into multiple new species) are central to general theory synthesizing ecology and macroevolution. Although competition for resources has long been viewed as the major mechanism by which natural selection would lead to divergence of organism traits, there are few conclusive examples of competition promoting speciation. The proposed research will provide a rare and strong test of the ecological speciation hypothesis in a system of co-occurring spadefoot toad species.Specifically, it will test whether competition among larvae of the spadefoot toads, Spea bombifrons and S. multiplicata, is leading to ecological speciation. This research will evaluate the general hypothesis that populations of S. multiplicata that do and do not occur with S. bombifrons are becoming reproductively isolated from one another because of contrasting competitive pressures faced by their larvae. The goals will be to test the following three predictions: (1) hybrids from crosses between populations should be less fit than offspring from matings within populations because of selection against hybrids; (2) traits under divergent selection between environments should influence mate choice and thereby form the basis of reproductive isolation; and (3) divergence in these traits should evolve in parallel in different populations that experience similar selective pressures. This project will form a decisive test of ecological speciation and will enhance our understanding of how competition promotes adaptive radiation. This study will, therefore, help explain the origins of diversity, which is one of the most challenging issues confronting biologists.