Runemark Anna, Fernández Laura Piñeiro, Eroukhmanoff Fabrice, Sætre Glenn-Peter
Am Nat. 2018 Jul;192(1):10-22. doi: 10.1086/697563. Epub 2018 Apr 23.
Hybridization is increasingly recognized as a potent evolutionary force. Although additive genetic variation and novel combinations of parental genes theoretically increase the potential for hybrid species to adapt, few empirical studies have investigated the adaptive potential within a hybrid species. Here, we address whether genomic contingencies, adaptation to climate, or diet best explain divergence in beak morphology using genomically diverged island populations of the homoploid hybrid Italian sparrow Passer italiae from Crete, Corsica, and Sicily. Populations vary significantly in beak morphology both between and within islands of origin. Temperature seasonality best explains population divergence in beak size. Interestingly, beak shape along all significant dimensions of variation was best explained by annual precipitation, genomic composition, and their interaction, suggesting a role for contingencies. Moreover, beak shape similarity to a parent species correlates with proportion of the genome inherited from that species, consistent with the presence of contingencies. In conclusion, adaptation to local conditions and genomic contingencies arising from putatively independent hybridization events jointly explain beak morphology in the Italian sparrow. Hence, hybridization may induce contingencies and restrict evolution in certain directions dependent on the genetic background.
杂交越来越被认为是一种强大的进化力量。虽然从理论上讲，加性遗传变异和亲本基因的新组合会增加杂交物种适应的潜力，但很少有实证研究调查杂交物种内部的适应潜力。在这里，我们利用来自克里特岛、科西嘉岛和西西里岛的基因组分化的同倍体杂交意大利麻雀（Passer italiae）的岛屿种群，探讨基因组偶然性、对气候的适应或饮食是否最能解释喙形态的差异。在起源岛屿之间和岛屿内部，种群的喙形态存在显著差异。温度季节性最能解释喙大小的种群差异。有趣的是，沿着所有显著变异维度的喙形状最好由年降水量、基因组组成及其相互作用来解释，这表明偶然性起到了作用。此外，与亲本物种的喙形状相似性与从该物种继承的基因组比例相关，这与偶然性的存在一致。总之，对当地条件的适应以及假定独立杂交事件产生的基因组偶然性共同解释了意大利麻雀的喙形态。因此，杂交可能会引发偶然性，并根据遗传背景限制某些方向的进化。
