title: On the Coyne and Orr-igin of species: effects of intrinsic postzygotic isolation, ecological differentiation, x chromosome size, and sympatry on Drosophila speciation.
abstract: Coyne and Orr found that mating discrimination (premating isolation) evolves much faster between sympatric than allopatric Drosophila species pairs. Their meta-analyses established that this pattern, expected under reinforcement, is common and that Haldane's rule is ubiquitous in Drosophila species divergence. We examine three possible contributors to the reinforcement pattern: intrinsic postzygotic isolation, dichotomized as to whether hybrid males show complete inviability/sterility; host-plant divergence, as a surrogate for extrinsic postzygotic isolation; and X chromosome size, whether roughly 20% or 40% of the genome is X-linked. We focus on "young" species pairs with overlapping ranges, contrasted with allopatric pairs. Using alternative criteria for "sympatry" and tests that compare either level of prezygotic isolation in sympatry or frequency of sympatry, we find no statistically significant effects associated with X chromosome size or our coarse quantifications of intrinsic postzygotic isolation or ecological differentiation. Although sympatric speciation seems very rare in animals, the pervasiveness of the reinforcement pattern and the commonness of range overlap for close relatives indicate that speciation in Drosophila is often not purely allopatric. It remains to determine whether increased premating isolation with sympatry results from secondary contact versus parapatric speciation and what drives this pattern.
authors: Department of Evolution and Ecology and Center for Population Biology, University of California, Davis, California, 95616. mturelli@ucdavis.edu.
authors: Michael
authors: M
authors: Turelli
authors: Jeremy R
authors: JR
authors: Lipkowitz
authors: Yaniv
authors: Y
authors: Brandvain
mesh_terms: D000818:Animals; D005075:Biological Evolution; D004330:Drosophila / Q000235:genetics*; D017753:Ecosystem; D005260:Female; D005843:Geography; D006824:Hybridization, Genetic; D007246:Infertility; D008297:Male; D060047:Reproductive Isolation; D061350:Sympatry; D014960:X Chromosome
keywords: Allopatry; Dobzhansky-Muller incompatibilities (DMIs); extrinsic postzygotic isolation; parapatric speciation; reinforcement