Data from: Extensive phenotypic diversification coexists with little genetic divergence and a lack of population structure in the White Wagtail subspecies complex (Motacilla alba)

Geographically clustered phenotypes often demonstrate consistent patterns in molecular markers, particularly mitochondrial DNA (mtDNA) traditionally used in phylogeographic studies. However distinct evolutionary trajectories among traits and markers can lead to their discordance. First, geographic structure in phenotypic traits and nuclear molecular markers can be co-aligned but inconsistent with mtDNA (mito-nuclear discordance). Alternatively, phenotypic variation can have little to do with patterns in neither mtDNA nor nuclear markers. Disentangling between these distinct patterns can provide insight into the role of selection, demography and gene flow in population divergence. Here we examined a previously reported case of strong inconsistency between geographic structure in mtDNA and plumage traits in a widespread polytypic bird species, the White Wagtail (Motacilla alba). We tested whether this pattern is due to mito-nuclear discordance or discrepancy between morphological evolution and both nuclear and mtDNA markers. We analyzed population differentiation and structure across six out of nine commonly recognized subspecies using 17 microsatellite loci and a combination of microsatellites and plumage indices in a comprehensively sampled region of a contact between two subspecies. We did not find support for the mito-nuclear discordance hypothesis: nuclear markers indicated a subtle signal of genetic clustering only partially consistent with plumage groups, similar to previous findings that relied on mtDNA. We discuss evolutionary factors that could have shaped the intricate patterns of phenotypic diversification in the White wagtail and the role that repeated selection on plumage “hotspots” and hybridization may have played.

地理聚类的表型通常与分子标记呈现一致的分布模式，其中线粒体DNA（mitochondrial DNA，mtDNA）是系统地理学研究（phylogeographic studies）中传统使用的经典分子标记。然而，性状与标记间迥异的演化轨迹可能导致二者的不一致性：其一，表型性状与核分子标记的地理结构可相互匹配，但与线粒体DNA不一致，即线粒体-核基因不一致性（mito-nuclear discordance）；其二，表型变异与线粒体DNA及核分子标记的分布模式均无关联。厘清这些不同的分布模式，有助于解析选择、种群动态与基因流在种群分化（population differentiation）中的作用。本研究针对此前报道的一个案例展开分析：广布多型鸟类物种（polytypic bird species）白鹡鸰（Motacilla alba）的线粒体DNA地理结构与羽衣性状存在显著不一致。我们检验了该模式究竟源于线粒体-核基因不一致性，还是形态演化与核分子及线粒体DNA标记间的不匹配。在两个亚种（subspecies）的接触带开展全面采样的前提下，我们利用17个微卫星位点（microsatellite loci），结合微卫星数据与羽衣性状指数（plumage indices），对9个公认亚种中的6个开展了种群分化与种群结构（population structure）分析。本研究未发现支持线粒体-核基因不一致性假说的证据：核分子标记仅显示出微弱的遗传聚类（genetic clustering）信号，且仅与羽衣类群部分匹配，这与此前基于线粒体DNA得到的研究结果一致。我们还讨论了可能塑造白鹡鸰表型多样化复杂模式的演化因素，以及羽衣性状“热点区域”的反复选择与杂交可能发挥的作用。