Peters K J, Myers S A, Dudaniec R Y, O'Connor J A, Kleindorfer S
School of Biological Sciences, Flinders University, Adelaide, SA, Australia.
Southern Seas Ecology Laboratory, School of Earth and Environmental Sciences, The University of Adelaide, Adelaide, SA, Australia.
J Evol Biol. 2017 Nov;30(11):1940-1952. doi: 10.1111/jeb.13167. Epub 2017 Sep 25.
The consequences of hybridization for biodiversity depend on the specific ecological and evolutionary context in which it occurs. Understanding patterns of gene flow among hybridizing species is crucial for determining the evolutionary trajectories of species assemblages. The recently discovered hybridization between two species of Darwin's tree finches (Camarhynchus parvulus and C. pauper) on Floreana Island, Galápagos, presents an exciting opportunity to investigate the mechanisms causing hybridization and its potential evolutionary consequences under conditions of recent habitat disturbance and the introduction of invasive pathogens. In this study, we combine morphological and genetic analysis with pairing observations to explore the extent, direction and drivers of hybridization and to test whether hybridization patterns are a result of asymmetrical pairing preference driven by females of the rarer species (C. pauper). We found asymmetrical introgression from the critically endangered, larger-bodied C. pauper to the common, smaller-bodied C. parvulus, which was associated with a lack of selection against heterospecific males by C. pauper females. Examination of pairing data showed that C. parvulus females paired assortatively, whereas C. pauper females showed no such pattern. This study shows how sex-specific drivers can determine the direction of gene flow in hybridizing species. Furthermore, our results suggest the existence of a hybrid swarm comprised of C. parvulus and hybrid birds. We discuss the influence of interspecific abundance differences and susceptibility to the invasive parasite Philornis downsi on the observed hybridization and recommend that the conservation of this iconic species group should be managed jointly rather than species-specific.
杂交对生物多样性的影响取决于其发生的特定生态和进化背景。了解杂交物种间的基因流动模式对于确定物种组合的进化轨迹至关重要。最近在加拉帕戈斯群岛的弗洛雷纳岛上发现了两种达尔文树雀（小树雀和大嘴树雀）之间的杂交现象，这为研究在近期栖息地干扰和入侵病原体引入的条件下导致杂交的机制及其潜在进化后果提供了一个令人兴奋的机会。在本研究中，我们将形态学和遗传学分析与配对观察相结合，以探索杂交的程度、方向和驱动因素，并测试杂交模式是否是由较稀有物种（大嘴树雀）的雌性驱动的不对称配对偏好的结果。我们发现，极度濒危、体型较大的大嘴树雀向常见、体型较小的小树雀发生了不对称基因渗入，这与大嘴树雀雌性对异种雄性缺乏选择有关。对配对数据的检查表明，小树雀雌性进行同配交配，而大嘴树雀雌性则没有这种模式。这项研究展示了性别特异性驱动因素如何决定杂交物种间基因流动的方向。此外，我们的结果表明存在一个由小树雀和杂交鸟类组成的杂交群体。我们讨论了种间丰度差异和对入侵寄生虫暗腹细蠓易感性对观察到的杂交的影响，并建议对这个标志性物种群体的保护应进行联合管理，而不是针对特定物种。
