Article,
The Genomics of Speciation in Drosophila: Diversity, Divergence, and Introgression Estimated Using Low-Coverage Genome Sequencing
PLoS Genet, 5 (7): e1000550 (July 2009)
DOI: 10.1371/journal.pgen.1000550
Abstract
The transformation of populations into distinct species depends on whether hybridization, recombination, and subsequent gene introgression can be suppressed between diverging species. We use partial genome sequences to reconstruct this evolutionary process in the <italic>Drosophila pseudoobscura</italic> species subgroup, which includes the hybridizing species pair <italic>D. pseudoobscura pseudoobscura</italic> and <italic>D. persimilis</italic>. Recent models suggest that chromosomal inversions can facilitate the persistence of hybridizing species because of their effects on recombination, whereby inverted regions would exhibit higher nucleotide divergence than non-inverted regions. Indeed, <italic>D. pseudoobscura-D. persimilis</italic> nucleotide divergence outside these inverted regions is lower than within or near inversions, resembling <italic>D. ps. pseudoobscura</italic> levels of within-species nucleotide diversity. We also observe that recombination suppression in F<sub>1</sub> hybrids extends greater than 2 Mbp outside the inversion breakpoints. Furthermore, when genomic sequence of <italic>D. persimilis</italic> is compared to two sister subspecies—the hybridizing subspecies, <italic>D. ps. pseudoobscura</italic>, and a non-hybridizing control subspecies, <italic>D. ps. bogotana</italic>—autosomal divergence is lower in the former, demonstrating recent gene exchange. These lines of evidence support a speciation model in which the two hybridizing species persist despite the presence of recent genic introgression in collinear regions of the genome because of the reduced recombinational effects of the inversions that distinguish them.
