Sympatric Speciation via Host or Habitat Specialization: An Experimental Test

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A contentious issue in biology is whether speciation, the splitting of one species into two, can occur when no geographic barrier separates the incipient species. Speciation without geographic isolation has been hypothesized to occur in plant-feeding insects that use the host as a rendezvous for mating: if a population diverges into two populations that feed on different hosts, the resulting populations will no longer encounter each other. The proposed work will investigate whether divergence in host preference and consequent mating isolation can occur in a laboratory population of the common fruit fly, Drosophila melanogaster. In each generation, unmated flies will be allowed to choose between two hosts that require different fly attributes for successful breeding. Mating will take place only between flies that chose the same host. The extent to which the experimental population splits into two populations with different host preferences will be monitored.The results will aid biologists' understanding of the mechanisms of species formation in plant-feeding insects, one of the most diverse groups of organisms on earth. The results will also shed light on the mechanisms by which insect species that feed on non-crop species can form new races on crop species.