Data from: Asymmetric introgression in a spotted salamander hybrid zone

Before the establishment of reproductive isolation, deeply diverged intraspecific lineages can experience complex genetic and behavioral interactions as they come into secondary contact. Divergent selective and demographic processes mediate gene flow among lineages, resulting in hybrid zones with complex biogeographic structure. Discordance in the biogeographic patterns of autosomal and maternally inherited loci provides a useful window to infer the processes mediating admixture and introgression across hybrid zones. Here, we sampled 489 genotypes across a hybrid zone between 2 phylogeographic lineages of the spotted salamander, Ambystoma maculatum, and characterize discordant patterns of nuclear and mitochondrial introgression across the contact boundary. Our results indicate asymmetric introgression of nuclear DNA beyond the contact boundary from the western to eastern lineage, with introgression of eastern mitochondrial DNA into the western lineage. We discuss alternative mechanisms for this pattern and attribute this result to neutral patterns of population expansion of the western lineage into the east in combination with female mate choice for larger-bodied western males. Our results underscore the complexity of interacting mechanisms that give rise to reproductive asymmetries in the earliest stages of the speciation process.

在生殖隔离（reproductive isolation）建立之前，分化程度较深的种内谱系在发生次生接触时，会发生复杂的遗传与行为互作。分化的选择压力与种群动态过程会调控谱系间的基因流，进而形成具有复杂生物地理结构的杂交带（hybrid zone）。常染色体与母系遗传位点的生物地理模式不一致，为推断杂交带内基因混合（admixture）与渐渗（introgression）的调控过程提供了有效途径。本研究对斑点钝口螈（Ambystoma maculatum）两个系统地理谱系间的杂交带内489个基因型样本进行了采样与分析，并刻画了接触边界两侧核基因（nuclear）与线粒体DNA（mitochondrial DNA）渐渗的不一致模式。研究结果显示，核DNA存在跨接触边界从西谱系向东谱系的不对称渐渗，而东部线粒体DNA则渐渗入西部谱系中。本研究探讨了该模式的多种潜在形成机制，并将该结果归因于西部谱系向东扩张的中性种群动态，与雌性偏好选择体型更大的西部雄性进行交配的行为共同作用。本研究结果凸显了物种形成早期阶段，驱动生殖不对称的互作机制的复杂性。