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.

近缘物种间的二次接触可产生遗传层面的影响。对必需资源的竞争可能促使可遗传性状发生分化，从而降低种间竞争强度，进一步加剧遗传分化；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）的种群展开分析，聚焦其在2013年与其亲本之一的西班牙麻雀（P. hispaniolensis）发生二次接触前后的变化。本研究证实了种间竞争的显著影响：意大利麻雀被亲本物种从热门觅食地排挤，导致其身体状况恶化，种群规模显著下降。尽管未检测到显著的形态学变化，但仅经过3年的同域共存，意大利麻雀在81个蛋白编码基因的集合上已与西班牙麻雀发生显著遗传分化。这种随时间推移产生的遗传分化，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模式一致。与微异域分布的个体相比，同域分布的意大利麻雀与西班牙麻雀之间的遗传分化程度更高。值得注意的是，在时间或空间维度的对比中筛选出的6个显著异常基因（即与西班牙麻雀分化程度最高的基因），均被证实与其他物种的学习能力及神经发育相关。