Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming.
Program in Ecology, University of Wyoming, Laramie, Wyoming.
Mol Ecol. 2019 Apr;28(7):1692-1708. doi: 10.1111/mec.15043.
In hybrid zones in which two divergent taxa come into secondary contact and interbreed, selection can maintain phenotypic diversity despite widespread genetic introgression. Red-breasted (Sphyrapicus ruber) and red-naped (S. nuchalis) sapsuckers meet and hybridize along a narrow contact zone that stretches from northern California to southern British Columbia. We found strong evidence for changes in the structure of this hybrid zone across time, with significant temporal shifts in allele frequencies and in the proportions of parental phenotypes across the landscape. In addition to these shifts, we found that differences in plumage predict genetic differences (R = 0.80), suggesting that plumage is a useful proxy for assessing ancestry. We also found a significant bimodal distribution of hybrids across the contact zone, suggesting that premating barriers may be driving reproductive isolation, perhaps as a result of assortative mating based on plumage differences. However, despite evidence of selection and strong patterns of population structure between parental samples, we found only weak patterns of genetic divergence. Using museum specimens and genomic data, this study of sapsuckers provides insight into the ways in which phenotypic and genetic structure have changed over a 40-year period, as well as insight into the mechanisms that may contribute to the maintenance of the hybrid zone over time.
在两个具有分歧的分类单元发生次级接触和杂交的杂种区内，尽管存在广泛的遗传渐渗，但选择可以维持表型多样性。红胸（Sphyrapicus ruber）和红冠（S. nuchalis）吸汁啄木鸟在从加利福尼亚北部延伸到不列颠哥伦比亚省南部的狭窄接触区内相遇并杂交。我们发现了强有力的证据表明，随着时间的推移，这种杂种区的结构发生了变化，在景观上的等位基因频率和亲本表型的比例都发生了显著的时间变化。除了这些变化之外，我们还发现羽毛的差异可以预测遗传差异（R = 0.80），这表明羽毛是评估祖先的有用指标。我们还发现，杂种在接触区内呈现出双峰分布，这表明，可能是由于基于羽毛差异的选择性交配导致了交配前的隔离障碍，从而促进了生殖隔离。然而，尽管有选择的证据和父母样本之间强烈的种群结构模式，但我们只发现了微弱的遗传分化模式。通过对啄木鸟的研究，这项利用博物馆标本和基因组数据的研究深入了解了表型和遗传结构在 40 年间的变化方式，以及可能有助于杂种区随时间维持的机制。
