Data from: Hybridization at an ecotone: ecological and genetic barriers between three Iberian vipers

The formation of stable genetic boundaries between emerging species is often diagnosed by reduced hybrid fitness relative to parental taxa. This reduced fitness can arise from endogenous and/or exogenous barriers to gene flow. Although detecting exogenous barriers in nature is difficult, we can estimate the role of ecological divergence in driving species boundaries by integrating molecular and ecological niche modelling tools. Here, we focus on a three-way secondary contact zone between three viper species (Vipera aspis, V. latastei and V. seoanei) to test for the contribution of ecological divergence to the development of reproductive barriers at several species traits (morphology, nuclear DNA, and mitochondrial DNA). Both the nuclear and mitochondrial data show that all taxa are genetically distinct and that the sister species V. aspis and V. latastei hybridize frequently and backcross over several generations. We find that the three taxa have diverged ecologically and meet at a hybrid zone coincident with a steep ecotone between the Atlantic and Mediterranean biogeographic provinces. Integrating landscape and genetic approaches, we show that hybridization is spatially restricted to habitats that are sub-optimal for parental taxa. Together, these results suggest that niche separation and adaptation to an ecological gradient confer an important barrier to gene flow among taxa that have not achieved complete reproductive isolation.

新兴物种间稳定遗传界限的判定，通常以相较于亲本类群的杂交适合度（hybrid fitness）降低为依据。这类适合度降低可由基因流的内源和/或外源障碍引发。尽管在自然环境中检测外源障碍颇具难度，但我们可通过整合分子生物学与生态位建模（ecological niche modelling）工具，评估生态分化在塑造物种界限中所发挥的作用。本研究聚焦于三种蝰蛇（Vipera aspis、V. latastei与V. seoanei）之间的三方次生接触带（secondary contact zone），旨在检验生态分化对多个物种性状（形态学、核DNA以及线粒体DNA）层面生殖隔离形成的贡献。核DNA与线粒体DNA数据均显示，所有类群均存在遗传分化，且姐妹种极北蝰（Vipera aspis）与拉氏蝰（Vipera latastei）会频繁杂交并历经多代回交（backcross）。研究发现，三种类群均发生了生态分化，并形成了与大西洋与地中海生物地理区之间陡峭生态交错带（ecotone）相吻合的杂交带。通过整合景观遗传学方法，我们证实杂交事件在空间上局限于对亲本类群而言并非最优的生境之中。综合以上结果，本研究表明，生态位分化与对生态梯度的适应性，为尚未达成完全生殖隔离（reproductive isolation）的类群之间的基因流构建了重要障碍。