The diversity of life surrounds us. Speciation is the process by which biodiversity originates. Differences among species or distinct populations are perhaps the most observable manifestations of the evolutionary process. Speciation can occur via divergent natural selection (ie, ecological speciation), as Darwin (1859) initially hypothesized, or potentially via sexual selection as is supported in theory (Lande 1981). Ecological speciation is currently considered the most common mode of speciation and is evident in several study systems including fish and insects. Speciation via sexual selection, however, has theoretical support and only limited experimental support stemming from comparative studies.
I am broadly interested in the process of speciation and maintenance, or breakdown, of species boundaries. More specifically, my dissertation aims to address the potential role of sexual selection in the diversification of darters, a genus of small, benthic stream fishes. Darters are one of the most diverse groups of fishes in North America, being comprised of more than 150 species. Snubnose darters and closely related species (~28 species) are all sexually dichromatic, and species differ most markedly in male nuptial coloration.
To test the role of sexual selection in darter speciation, I will measure reproductive barriers (ie, ecological isolation, behavioral isolation, gametic incompatibility, hybrid inviability, and hybrid sterility) between 10 allopatric species pairs. Using a method pioneered by Coyne and Orr (1989), I can determine the evolutionary rate of each of the reproductive barriers. Provided sexual selection via coevolution of female preferences and male traits is the primary facilitator of speciation, I expect behavioral isolation to evolve faster than other reproductive barriers. In addition to this central objective, I also will address the role male nuptial color and other visual cues play in facilitating behavioral isolation via correlative studies.
Some focal species (at right) are: the Chickasaw (top), Bandfin, Splendid, Saffron, Coosa, Brighteye, and Eastrim (bottom) darters.