Data from: Rapid polygenic response to secondary contact in a hybrid species

Secondary contact between closely related species can have genetic consequences. Competition for essential resources may lead to divergence in heritable traits that reduces interspecific competition, thus leading to increased genetic divergence. Conversely, hybridization and backcrossing can lead to genetic convergence. Here we study a population of a hybrid species, the Italian sparrow (Passer italiae), before and after it came into secondary contact with one of its parent species, the Spanish sparrow (P. hispaniolensis), in 2013. We demonstrate clear consequences of interspecific competition: Italian sparrows became outcompeted from a popular feeding site by its parent species, resulting in poorer body condition and a significant drop in population size. Although no significant morphological change could be detected, after only 3 years of sympatry the Italian sparrows had diverged significantly from the Spanish sparrows across a set of 81 protein coding genes. These temporal genetic changes are mirrored by genetic divergence observed in older sympatric Italian sparrow populations within the same area of contact. Compared to microallopatric birds, sympatric ones are genetically more diverged from Spanish sparrows. Interestingly, all six significant outlier genes in the temporal or spatial comparison (i.e. those showing the greatest divergence from Spanish sparrows) have been found to be associated with learning and neural development in other species.

亲缘关系相近的物种间发生次级接触（secondary contact）可产生遗传学层面的效应。对必需资源的竞争可促使可遗传性状发生分化，进而降低种间竞争强度，最终加剧遗传分化；反之，杂交与回交则可能引发遗传趋同。本研究针对杂交物种意大利麻雀（Passer italiae）的一个种群，追踪了2013年该种群与其中一个亲本物种西班牙麻雀（P. hispaniolensis）发生次级接触前后的动态变化。研究证实了种间竞争的显著影响：意大利麻雀被亲本物种排挤离开一处热门觅食地，进而导致其身体状况变差、种群规模大幅下降。尽管未检测到显著的形态学变化，但仅经过3年的同域分布（sympatry）后，意大利麻雀在81个蛋白编码基因（protein coding genes）的序列上已与西班牙麻雀发生显著遗传分化。上述随时间推移出现的遗传分化模式，与同一接触区域内更古老的同域分布意大利麻雀种群所观测到的遗传分化结果高度一致。相较于微异域（microallopatric）种群的个体，同域分布的意大利麻雀与西班牙麻雀间的遗传分化程度更高。有趣的是，在时间或空间维度的比较中筛选出的6个显著异常基因（即与西班牙麻雀序列分化程度最高的基因），在其他物种中均被证实与学习能力及神经发育密切相关。