Data from: Social selection parapatry in Afrotropical sunbirds

The extent of range overlap of incipient and recent species depends on the type and magnitude of phenotypic divergence that separates them, and the consequences of phenotypic divergence on their interactions. Signal divergence by social selection likely initiates many speciation events, but may yield niche-conserved lineages predisposed to limit each others’ ranges via ecological competition. Here we examine this neglected aspect of social selection speciation theory in relation to the discovery of a non-ecotonal species border between sunbirds. We find that Nectarinia moreaui and N. fuelleborni meet in a ∼6 km wide contact zone, as estimated by molecular cline analysis. These species exploit similar bioclimatic niches, but sing highly divergent learned songs, consistent with divergence by social selection. Cline analyses suggest that within-species stabilizing social selection on song-learning predispositions maintains species differences in song despite both hybridization and cultural transmission. We conclude that ecological competition between moreaui and fuelleborni contributes to the stabilization of the species border, but that ecological competition acts in conjunction with reproductive interference. The evolutionary maintenance of learned song differences in a hybrid zone recommend this study system for future studies on the mechanisms of learned song divergence and its role in speciation.

初期成种物种与新近形成物种的分布范围重叠程度，取决于区分二者的表型分化类型与强度，以及表型分化对二者种间相互作用所产生的影响。经由社会选择产生的信号分化，可能启动诸多成种事件，但也可能催生生态位保守的支系，这类支系易于通过生态竞争相互限制分布范围。本研究针对花蜜鸟之间发现的非生态交错带型物种边界，探讨社会选择成种理论中这一被忽视的研究维度。经分子梯度分析估算，我们发现莫罗花蜜鸟（Nectarinia moreaui）与富勒花蜜鸟（N. fuelleborni）在宽度约6千米的接触带内相遇。这两个物种占据相似的生物气候生态位，但拥有差异极大的习得鸣唱，这与社会选择介导的表型分化特征相符。梯度分析显示，尽管存在杂交与文化传递现象，物种内部针对鸣唱学习倾向的稳定型社会选择，仍维持了二者在鸣唱上的种间差异。本研究结论认为，莫罗花蜜鸟与富勒花蜜鸟之间的生态竞争，有助于物种边界的稳定，但生态竞争与生殖干扰共同发挥作用。杂交带内习得鸣唱差异的演化维持特性，使该研究系统成为未来探讨习得鸣唱分化机制及其在成种过程中作用的理想研究对象。