A sex chromosome polymorphism maintains divergent plumage phenotypes between extensively hybridizing yellowhammers (Emberiza citrinella) and pine buntings (E. leucocephalos)
Ellen Nikelski, Alexander S. Rubtsov, Darren Irwin
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引用次数: 0
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.
在同域物种分化中,一个物种的种群被地理屏障隔离,并通过基因分化形成生殖隔离。当种群在二次接触中相遇时,进化出的生殖屏障的强度决定了杂交的程度,也决定了种群是继续分化还是融合在一起。黄椋鸟(Emberiza citrinella)和松鹀(E. leucocephalos)是鸟类的姊妹物种,它们在更新世冰川时期分居于欧亚大陆的两侧。虽然它们在羽色上有很大差异,并在异源繁殖中形成了不同的基因群,但这些类群的线粒体DNA分化几乎可以忽略不计,而且在西伯利亚中部它们重叠的地方发生了广泛的杂交,这给该系统的生殖隔离状态带来了不确定性。为了评估类群间生殖隔离的强度,我们研究了整个系统的基因组分化。我们发现在同域中发生了广泛的混交,这表明类群之间的生殖隔离很弱。我们还确定了一个推定的 Z 染色体反转区域,该区域是该系统羽色变异的基础,"松鹀 "单倍型比 "黄锤 "单倍型占优势。我们的研究结果表明,黄锤和松鹀目前正处于十字路口,进化的力量可能会推动该系统继续分化或种群合并。然而,即使这些类群合并,推定的染色体 Z 反转单倍型之间的重组抑制可能会维持该系统内不同的羽色表型。因此,我们的发现凸显了杂交在增加遗传和表型变异以及系统可进化性方面的重要作用。
期刊介绍:
Molecular Ecology publishes papers that utilize molecular genetic techniques to address consequential questions in ecology, evolution, behaviour and conservation. Studies may employ neutral markers for inference about ecological and evolutionary processes or examine ecologically important genes and their products directly. We discourage papers that are primarily descriptive and are relevant only to the taxon being studied. Papers reporting on molecular marker development, molecular diagnostics, barcoding, or DNA taxonomy, or technical methods should be re-directed to our sister journal, Molecular Ecology Resources. Likewise, papers with a strongly applied focus should be submitted to Evolutionary Applications. Research areas of interest to Molecular Ecology include:
* population structure and phylogeography
* reproductive strategies
* relatedness and kin selection
* sex allocation
* population genetic theory
* analytical methods development
* conservation genetics
* speciation genetics
* microbial biodiversity
* evolutionary dynamics of QTLs
* ecological interactions
* molecular adaptation and environmental genomics
* impact of genetically modified organisms