A TEST OF THE CHROMOSOMAL REARRANGEMENT MODEL OF SPECIATION IN DROSOPHILA PSEUDOOBSCURA

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Abstract
Recent studies suggest that chromosomal,rearrangements,play a significant role in speciation by preventing recombination,and maintaining,species persistence despite interspecies gene flow. Factors conferring adaptation or reproductive isolation are maintained in rearranged regions in the face of hybridization, while such factors are elim- inated from collinear regions. As a direct test of this rearrangement model, we evaluated the genetic basis of hybrid male sterility in a sympatric species pair, Drosophila pseudoobscura pseudoobscuraand D. persimilis, and an allopatric species pair, D. pseudoobscura bogotanaand D. persimilis. Our results are consistent with the proposed model: virtually all of the sterility factors in the former pair are associated with three inverted regions, whereas sterility factors are present in the collinear regions in the latter pair. These findings,indicate recombination,and,selection may,have eliminated sterility factors outside the inverted regions between D. p. pseudoobscura and D. persimilis, suggesting chromosomal,rearrangements,may,facilitate species persistence despite hybridization. Key words. Chromosomal inversions, Drosophila persimilis, Drosophila pseudoobscura, hybrid sterility, speciation. Received March 12, 2004. Accepted May 5, 2004. Because the process of speciation is rarely observed, we