Males will court just about anything, but females mate preferentially with their own species. This, at least, is true for two species of the fruitfly Drosophila (D.pseudoobscura and D. persimilis) that occur in the same environment along the western United States and can interbreed where they meet. In the open-access journal PLoS Biology, Daniel Ortiz-Barrientos and his colleagues present the first high-resolution analysis of "species reinforcement genes" that account for heightened discrimination by females in populations faced with a choice, compared with their isolated peers.
The researchers identify two new loci that influence the likelihood that a female will choose to mate with a male of her own species, rather than one of a closely related species. Because the daughters of discriminating D. pseudoobscura females were just as discriminating as their mothers, they concluded that female mating discrimination is inherited as a dominant trait. They further show that genes responsible for female preference are on the X and fourth chromosomes. The most promising genes in both regions appear to be involved with olfaction and on this basis, the authors propose a novel model of speciation via mating discrimination in Drosophila pseudoobscura based on the combined response to auditory and olfactory cues.
These findings mark a major turning point in the study of speciation as they provide vital clues to the final stages of the speciation process. Ortiz-Barrientos and colleagues are now poised to identify and study the evolution of the actual genes contributing to the creation of new species.
Citation: Ortiz-Barrientos D, Counterman B, Noor M (2004) The Genetics of Speciation by Reinforcement. PLoS Biol 2 (12): e416.
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