Data from: Sharp acoustic boundaries across an altitudinal avian hybrid zone despite asymmetric introgression

Birdsong is a sexually selected trait that could play an important evolutionary role when related taxa come into secondary contact. Many songbird species however learn their songs through copying one or more tutors, which complicates the evolutionary outcome of such contact. Two subspecies of a presumed vocal learner, the grey-breasted wood-wren (Henicorhina leucophrys), replace each other altitudinally across the western slope of the Ecuadorian Andes. These subspecies are morphologically very similar, but show striking differences in their song. We examined variation in acoustic traits and genetic composition across the altitudinal range covered by both subspecies and between two allopatric populations. The acoustic boundary between the subspecies was found to be highly abrupt across a narrow elevational range with virtually no evidence of song convergence. Mixed singing and use of hetero-subspecific song occurred in the contact zone and was biased towards the use of leucophrys song types. Hetero-subspecific song copying by hilaris and not by leucophrys reflected a previously found asymmetric pattern of response to song playback. Using AFLP markers, we detected hybridization in the contact zone and asymmetric introgression in parapatric populations, with more leucophrys alleles present in hilaris populations than vice versa. This pattern may be a trail of introgression due to upslope displacement of leucophrys by hilaris. Our data suggest that song learning may impact speciation and hybridization in contrasting ways at different spatial scales: while learning may speed up population divergence in songs, thereby enhancing assortative mating and reducing gene flow, it may at a local level also lead to the copying of heterospecific songs, therefore allowing some level of hybridization and introgression.

鸣唱是受性选择调控的性状，当近缘类群发生次生接触时，其可能发挥重要的进化作用。然而，多数鸣禽物种通过模仿一位或多位鸣唱导师来习得鸣唱，这使得此类接触的进化结果变得更为复杂。灰胸苇鹪鹩（Henicorhina leucophrys）被认为是鸣唱学习者，其下两个亚种沿厄瓜多尔安第斯山脉西坡的海拔梯度形成相互替代的分布格局。这两个亚种形态极为相似，但鸣唱却存在显著差异。我们针对两个亚种的完整海拔分布范围，以及两个异域种群间的声学性状与遗传组成差异开展了研究。研究发现，两个亚种间的声学边界在狭窄的海拔区间内呈现极强的陡变特征，几乎无鸣唱趋同的迹象。接触带内存在混合鸣唱以及异亚种鸣唱的使用现象，且该现象更偏向于使用leucophrys亚种的鸣唱类型。hilaris亚种（而非leucophrys亚种）会模仿异亚种鸣唱，这与此前发现的鸣唱回放响应不对称模式相一致。我们利用AFLP（扩增片段长度多态性，Amplified Fragment Length Polymorphism）标记，在接触带中检测到杂交事件，并在邻域种群中发现了不对称渐渗现象：hilaris种群中携带的leucophrys等位基因数量显著多于反向情况。该模式可能是hilaris亚种将leucophrys亚种沿海拔向上排挤后所留下的渐渗痕迹。我们的研究数据表明，鸣唱学习在不同空间尺度下，会以截然相反的方式影响物种形成与杂交过程：一方面，鸣唱学习可加速种群间的鸣唱分化，进而强化选型交配并减少基因交流；另一方面，在局域尺度下，鸣唱学习也可能促使个体模仿异种鸣唱，从而为一定程度的杂交与渐渗提供了可能。