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International Journal of Evolutionary Biology
Volume 2012 (2012), Article ID 285468, 9 pages
http://dx.doi.org/10.1155/2012/285468
Research Article

Rapid Evolution of Assortative Fertilization between Recently Allopatric Species of Drosophila

1Department of Biology, The University of Iowa, Iowa City, IA 52242, USA
2Department of Biology, University of Rochester, Rochester, NY 14627-0211, USA

Received 15 July 2011; Accepted 11 October 2011

Academic Editor: Artyom Kopp

Copyright © 2012 Yasir H. Ahmed-Braimah and Bryant F. McAllister. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The virilis group of Drosophila represents a relatively unexplored but potentially useful model to investigate the genetics of speciation. Good resolution of phylogenetic relationships and the ability to obtain fertile hybrid offspring make the group especially promising for analysis of genetic changes underlying reproductive isolation separate from hybrid sterility and inviability. Phylogenetic analyses reveal a close relationship between the sister species, Drosophila americana and D. novamexicana, yet excepting their contemporary allopatric distributions, factors that contribute to reproductive isolation between this species pair remain uncharacterized. A previous report has shown reduced progeny numbers in laboratory crosses between the two species, especially when female D. novamexicana are crossed with male D. americana. We show that the hatch rate of eggs produced from heterospecific matings is reduced relative to conspecific matings. Failure of eggs to hatch, and consequent reduction in hybrid progeny number, is caused by low fertilization success of heterospecific sperm, thus representing a postmating, prezygotic incompatibility. Following insemination, storage and motility of heterospecific sperm is visibly compromised in female D. novamexicana. Our results provide evidence for a mechanism of reproductive isolation that is seldom reported for Drosophila species, and indicate the rapid evolution of postmating, prezygotic reproductive barriers in allopatry.