AI Article Synopsis
- Under allopatric speciation, species are isolated by geographic barriers, leading to genetic changes and potential reproductive isolation.
- The yellowhammer and pine bunting diverged during the Pleistocene but have shown weak reproductive barriers, as evidenced by extensive hybridization in their overlapping regions of Siberia.
- Genomic analysis indicates that admixture is significant, suggesting that the two species might either continue to differentiate or merge, while also revealing a genetic inversion linked to plumage variation that could preserve these differences even if they do merge.
Article Abstract
Under allopatric speciation, populations of a species become isolated by a geographic barrier and develop reproductive isolation through genetic differentiation. When populations meet in secondary contact, the strength of evolved reproductive barriers determines the extent of hybridization and whether the populations will continue to diverge or merge together. The yellowhammer (Emberiza citrinella) and pine bunting (E. leucocephalos) are avian sister species that diverged in allopatry on either side of Eurasia during the Pleistocene glaciations. Though they differ greatly in plumage and form distinct genetic clusters in allopatry, these taxa show negligible mitochondrial DNA differentiation and hybridize extensively where they overlap in central Siberia, lending uncertainty to the state of reproductive isolation in the system. To assess the strength of reproductive barriers between taxa, we examined genomic differentiation across the system. We found that extensive admixture has occurred in sympatry, indicating that reproductive barriers between taxa are weak. We also identified a putative Z chromosome inversion region that underlies plumage variation in the system, with the 'pine bunting' haplotype showing dominance over the 'yellowhammer' haplotype. Our results suggest that yellowhammers and pine buntings are currently at a crossroads and that evolutionary forces may push this system towards either continued differentiation or population merging. However, even if these taxa merge, recombination suppression between putative chromosome Z inversion haplotypes may maintain divergent plumage phenotypes within the system. In this way, our findings highlight the important role hybridization plays in increasing the genetic and phenotypic variation as well as the evolvability of a system.
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| http://dx.doi.org/10.1111/mec.17526 | DOI Listing |
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