Data from: Willet be one species or two?: a genomic view of the evolutionary history of Tringa semipalmata

The Willet (Tringa semipalmata; Scolopacidae) is composed of 2 morphologically and vocally distinct subspecies with broadly disjunct breeding distributions in North America. Nominate T. s. semipalmata breeds in coastal salt and brackish marshes along the Atlantic and Gulf coasts of eastern North America and the West Indies, and T. s. inornata breeds in wet grasslands and prairies in the northwestern interior of North America. To assess divergence and test for hybridization between the 2 subspecies, we sampled breeding and wintering populations and collected morphological data, mitochondrial DNA sequences from the ND2 locus, and nuclear DNA sequences from genomic libraries enriched for ultraconserved elements (UCEs). Mitochondrial haplotypes were reciprocally monophyletic between the 2 subspecies and indicated divergence approximately 700,000 yr ago. The UCE dataset included 4,635 loci containing 19,322 single nucleotide polymorphisms (SNPs), and, based on these data, individuals clustered by subspecies with no evidence of admixture between them and no substructure within subspecies. We identified 42 nuclear loci that contained SNPs fixed for alternate alleles between the 2 subspecies. Of the 42 loci with fixed differences, a statistically disproportional 17 were Z-linked, indicating a role for sexual selection in the divergence of the 2 subspecies. Genetic, morphological, ecological, and behavioral differences suggest that the 2 Willet subspecies may merit treatment as separate species. Further studies are needed to determine the presence of pre- or post-mating reproductive isolation.威尔鹬（Willet，学名Tringa semipalmata；隶属于鹬科Scolopacidae）包含两个在形态学与声学上均具有显著差异的亚种，二者在北美大陆的繁殖分布区呈广泛间断格局。指名亚种T. s. semipalmata的繁殖栖息地为北美东部大西洋沿岸、墨西哥湾沿岸及西印度群岛的沿海盐沼与咸淡水沼泽；而T. s. inornata则繁殖于北美西北内陆的湿草甸与草原。 为评估这两个亚种的分化程度并检测其杂交情况，本研究采样了繁殖种群与越冬种群，收集了形态学数据、ND2基因座的线粒体DNA序列，以及通过富集超保守元件（ultraconserved elements, UCEs）构建的基因组文库获得的核DNA序列。线粒体单倍型在两个亚种间呈现相互单系性，提示二者的分化时间约为70万年前。 本次研究的超保守元件数据集包含4635个基因座，共涵盖19322个单核苷酸多态性位点（single nucleotide polymorphisms, SNPs）；基于该数据的聚类分析显示，个体可按亚种清晰分组，亚种间未检测到遗传混合现象，且亚种内部不存在遗传结构。本研究共鉴定出42个核基因座，其携带的单核苷酸多态性位点在两个亚种间为固定的等位基因差异。在这42个存在固定差异的基因座中，有17个为Z连锁基因座，这一比例在统计学上显著偏高，表明性选择在两个亚种的分化过程中发挥了重要作用。 遗传、形态、生态与行为层面的多重差异提示，这两个威尔鹬亚种或许应当被认定为独立物种。未来仍需开展进一步研究，以明确二者是否存在交配前或交配后生殖隔离。