Immigrant song: males and females learn songs post-dispersal in a tropical bird

A fundamental hypothesis about vocal learning is that young animals learn vocalizations in their natal areas and, following post-natal dispersal, they may introduce new types of vocalizations into their breeding areas. We tested this hypothesis in a tropical bird, the Rufous-and-white Wren (Thryophilus rufalbus), a species in which both sexes produce learned songs. We collected blood samples and acoustic recordings from 146 adult wrens from three populations in northwestern Costa Rica. We genotyped individuals at 10 polymorphic microsatellite loci and identified first-generation migrants using partial Bayesian genotype assignment. We quantified acoustic variation by comparing fine-scale acoustic structure, song sharing, and repertoire novelty between residents and first-generation migrants. We found significant population-level differences in acoustic structure of songs among the three populations. Of the 146 individuals genotyped, 9 individuals were identified as first-generation migrants. In contrast to our predictions, however, we found that these first-generation migrants did not exhibit differences in the acoustic structure of their songs from resident individuals in their breeding population, either for males or females. We conclude that song learning in first-generation migrants must be behaviourly influenced by birds in their breeding populations, following post-natal dispersal. We observed population-level acoustic differences among the three study sites, which implies sustained divergent selection pressures at each site, possibly reflecting acoustic adaptation to different environments or social pressure to sing local songs. Understanding and quantifying patterns of cultural evolution at multiple scales provides insight into how behavioural barriers, such as acoustic signals, contribute to population differentiation and even speciation.

关于发声学习的一项核心假说认为，幼年动物会在其出生区域习得鸣唱，而在产后扩散后，它们可能会将新型鸣唱引入其繁殖区域。我们以热带鸟类棕白鹪鹩（Thryophilus rufalbus）为研究对象检验了该假说，该物种的雌雄个体均能习得鸣唱。我们从哥斯达黎加西北部的三个种群中采集了146只成年鹪鹩的血液样本与声学录音，对10个多态性微卫星位点进行个体基因分型，并通过部分贝叶斯基因型分配法鉴定第一代迁入者。我们通过比较留居个体与第一代迁入者的精细声学结构、鸣唱共享情况以及曲目新颖性，量化了声学变异。研究发现，三个种群间的鸣唱声学结构存在显著的种群水平差异。在完成基因分型的146只个体中，共有9只被鉴定为第一代迁入者。然而与我们的预测相悖的是，无论雌雄，这些第一代迁入者的鸣唱声学结构与其繁殖区域内的留居个体均无显著差异。据此我们推断，产后扩散后的第一代迁入者，其鸣唱学习必然会受到繁殖区域内其他鸟类的行为影响。我们在三个研究区域间观测到了种群水平的声学差异，这意味着每个区域均存在持续的歧化选择压力，这可能反映了鸣唱对不同环境的声学适应，或是遵循当地鸣唱模式的社会压力。理解并量化多尺度下的文化演化模式，有助于揭示包括声学信号在内的行为障碍如何推动种群分化乃至物种形成。