Data from: Behavioral response to song and genetic divergence in two subspecies of white-crowned sparrows (Zonotrichia leucophrys)

Divergence in sexual signals may drive reproductive isolation between lineages, but behavioral barriers can weaken in contact zones. Here, we investigate the role of song as a behavioral and genetic barrier in a contact zone between two subspecies of white-crowned sparrows (Zonotrichia leucophrys). We employed a reduced genomic dataset to assess population structure and infer the history underlying divergence, gene flow and hybridization. We also measured divergence in song and tested behavioral responses to song using playback experiments within and outside the contact zone. We found that the subspecies form distinct genetic clusters, and demographic inference supported a model of secondary contact. Song phenotype, particularly length of the first note (a whistle), was a significant predictor of genetic subspecies identity and genetic distance along the hybrid zone, suggesting a close link between song and genetic divergence in this system. Individuals from both parental and admixed localities responded significantly more strongly to their own song than to the other subspecies song, supporting song as a behavioral barrier. Putative parental and admixed individuals were not significantly different in their strength of discrimination between own and other songs; however, individuals from admixed localities tended to discriminate less strongly, and this difference in discrimination strength was explained by song dissimilarity as well as genetic distance. Therefore, we find that song acts as a reproductive isolating mechanism that is potentially weakening in a contact zone between the subspecies. Our findings also support the hypothesis that intra-specific song variation can reduce gene flow between populations.

性信号的分化可驱动不同演化支间的生殖隔离，但在种群接触带中，这类行为障碍可能会趋于减弱。本研究以两种白顶麻雀（Zonotrichia leucophrys）的亚种接触带为研究对象，探讨鸣声作为行为与遗传屏障的作用。我们借助简化基因组数据集评估种群结构，并推断分化、基因流与杂交的演化历史背景。同时，我们测定了鸣声的分化程度，并在接触带内外开展鸣声回放实验，检验受试个体对不同鸣声的行为响应。结果表明，两个亚种各自形成独立的遗传聚类簇，种群历史推断结果支持次级接触演化模型。鸣声表型，尤其是首个哨音音节的时长，能够显著预测杂交带内的亚种遗传身份与遗传距离，提示该系统中鸣声与遗传分化存在紧密关联。来自亲本种群分布区与混合种群分布区的个体，对同种鸣声的响应强度均显著高于异种鸣声，证实鸣声可作为有效的行为隔离屏障。疑似亲本个体与混合种群个体在同种与异种鸣声的辨别强度上并无显著差异；但混合种群分布区的个体整体辨别强度偏弱，且该辨别强度差异可通过鸣声相似度与遗传距离进行解释。综上，本研究证实鸣声可作为生殖隔离机制，且在该亚种接触带中其隔离作用正逐渐减弱。本研究结果同时支持这一假说：种内鸣声变异可降低种群间的基因流。