Mechanisms of Speciation

Copyright © 2012 Kyoichi Sawamura et al. 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. " Speciation " was largely " speculation " two decades ago, at least with respect to a detailed and comprehensive mechanis-tic understanding of the origin of new species. Despite elegant classical work examining the genetic basis of interspe-cific differences and reproductive isolation and complementary studies of the ecological factors that can contribute to species divergence, speciation researchers lacked the tools to dissect the specific forces, traits, and genes involved. Thanks to the recent advances in molecular biology and genomic sequencing, detailed study of speciation is becoming feasible in many animal and plant groups. In fact, a dozen of " speciation genes " responsible for reproductive isolation between sibling species have been identified at the molecular level. Further, genetic changes leading to morphological differentiation among related species have been elucidated, supported by phylogenetic analyses at high resolution. We invited investigators to contribute both original research and review articles that would stimulate the continuing efforts to understand speciation and species differentiation from all perspectives, not only the genetic mechanisms but also the ecological and evolutionary causes. Among the seven original articles in this special issue, four were Drosophila studies. Two of them focus on the mechanisms of reproductive isolation. A. Takahashi et al. in " Cuticular hydrocarbon content that affects male mate preference of Drosophila melanogaster from west Africa " identified a polymorphic chemical cue involved in mate recognition between sibling species. Y. H. Ahmed-Braimah and B. F. McAllister in " Rapid evolution of assortative fertilization between recently allopatric species of Drosophila " described an example of postmating/prezygotic isolation, where heterospecific fertilization after mating is compromised due to disruptions in sperm storage and motility. Often, reproductive isolation evolves more rapidly than any morphological traits so that the only way to distinguish recently diverged species is through mating experiments. Y.-F. Li et al. in " DNA barcoding and molecular phylogeny of Drosophila lini and its sibling species " showed that molecular variation can also be widely shared between sibling species despite strong reproductive isolation between them. To understand why reproductive isolation can evolve so rapidly compared to other traits, L. Müller et al. in " Inter-and intraspecific variation in Drosophila genes with sex-biased expression " examined …