Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada.
National Museum of Natural Sciences, Spanish National Research Council (CSIC), Madrid, Spain.
Mol Ecol. 2018 Dec;27(23):4839-4855. doi: 10.1111/mec.14858. Epub 2018 Oct 1.
Detailed evaluations of genomic variation between sister species often reveal distinct chromosomal regions of high relative differentiation (i.e., "islands of differentiation" in F ), but there is much debate regarding the causes of this pattern. We briefly review the prominent models of genomic islands of differentiation and compare patterns of genomic differentiation in three closely related pairs of New World warblers with the goal of evaluating support for the four models. Each pair (MacGillivray's/mourning warblers; Townsend's/black-throated green warblers; and Audubon's/myrtle warblers) consists of forms that were likely separated in western and eastern North American refugia during cycles of Pleistocene glaciations and have now come into contact in western Canada, where each forms a narrow hybrid zone. We show strong differences between pairs in their patterns of genomic heterogeneity in F , suggesting differing selective forces and/or differing genomic responses to similar selective forces among the three pairs. Across most of the genome, levels of within-group nucleotide diversity (π ) are almost as large as levels of between-group nucleotide distance (π ) within each pair, suggesting recent common ancestry and/or gene flow. In two pairs, a pattern of the F peaks having low π suggests that selective sweeps spread between geographically differentiated groups, followed by local differentiation. This "sweep-before-differentiation" model is consistent with signatures of gene flow within the yellow-rumped warbler species complex. These findings add to our growing understanding of speciation as a complex process that can involve phases of adaptive introgression among partially differentiated populations.
对姐妹物种之间的基因组变异进行详细评估通常会揭示出明显的相对分化的染色体区域（即 F 中的“分化岛屿”），但对于这种模式的原因存在很多争议。我们简要回顾了基因组分化岛屿的突出模型，并比较了三个密切相关的新世界莺属对的基因组分化模式，目的是评估这四个模型的支持程度。每对（麦吉利夫雷氏/哀婉莺；汤森氏/黑喉绿莺；和奥杜邦氏/紫蓝莺）都由在更新世冰川周期中可能在北美西部和东部避难所中分离的形式组成，现在已经在加拿大西部接触，在那里每个形式形成一个狭窄的杂交带。我们展示了 F 中基因组异质性模式在三个对之间存在强烈差异，表明选择力不同和/或对三种对中类似选择力的基因组反应不同。在基因组的大部分区域，组内核苷酸多样性（π）的水平几乎与每个对之间组间核苷酸距离（π）的水平一样大，这表明最近有共同的祖先和/或基因流。在两个对中，F 峰的低π模式表明，选择扫掠过地理分化的群体之间传播，然后是局部分化。这种“先分化后选择”的模型与黄腹莺种复合体中的基因流特征一致。这些发现增加了我们对物种形成作为一个复杂过程的理解，该过程可以涉及部分分化群体之间的适应性渗透阶段。
