Journal
MOLECULAR ECOLOGY
Volume 23, Issue 5, Pages 1124-1136Publisher
WILEY
DOI: 10.1111/mec.12678
Keywords
positive selection; speciation; gene flow; recurrent adaptation
Funding
- University of Iowa funds
- NIH Predoctoral Training Grant in Genetics [T32 GM008629014]
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Interspecific hybridization provides the unique opportunity for species to tap into genetic variation present in a closely related species and potentially take advantage of beneficial alleles. It has become increasingly clear that when hybridization occurs, mitochondrial DNA (mtDNA) often crosses species boundaries, raising the possibility that it could serve as a recurrent target of natural selection and source of species' adaptations. Here we report the sequences of 46 complete mitochondrial genomes of Drosophila yakuba and Drosophila santomea, two sister species known to produce hybrids in nature (~3%). At least two independent events of mtDNA introgression are uncovered in this study, including an early invasion of the D.yakuba mitochondrial genome that fully replaced the D.santomea mtDNA native haplotypes and a more recent, ongoing event centred in the hybrid zone. Interestingly, this recent introgression event bears the signature of Darwinian natural selection, and the selective haplotype can be found at low frequency in Africa mainland populations of D.yakuba. We put forward the possibility that, because the effective population size of D.santomea is smaller than that of D.yakuba, the faster accumulation of mildly deleterious mutations associated with Muller's ratchet in the former species may have facilitated the replacement of the mutationally loaded mitochondrial genome of D.santomea by that of D.yakuba.
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