Data from: Genetic and phenotypic divergence in an island bird: isolation by distance, by colonisation or by adaptation?

Discerning the relative roles of adaptive and non-adaptive processes in generating differences among populations and species, as well as how these processes interact, are fundamental aims in biology. Both genetic and phenotypic divergence across populations can be the product of limited dispersal and gradual genetic drift across populations (isolation by distance), of colonisation history and founder effects (isolation by colonisation) or of adaptation to different environments preventing migration between populations (isolation by adaptation). Here we attempt to differentiate between these processes using island populations of Berthelot's pipit (Anthus berthelotii), a passerine bird endemic to three Atlantic archipelagos. Using microsatellite markers and approximate Bayesian computation, we reveal that the northwards colonisation of this species ca 8,500 years ago resulted in genetic bottlenecks in the colonised archipelagos. We then show that high levels of genetic structure exist across archipelagos, and that these are consistent with a pattern of isolation by colonisation, but not with isolation by distance or adaptation. Finally, we show that substantial morphological divergence also exists and that this is strongly concordant with patterns of genetic structure and bottleneck history, but not with environmental differences or geographic distance. Overall our data suggest that founder effects are responsible for both genetic and phenotypic changes across archipelagos. Our findings provide a rare example of how founder effects can persist over evolutionary timescales, and suggest that they may play an important role in the early stages of speciation.

厘清适应性与非适应性过程在种群和物种间差异产生中的相对作用，以及这些过程的相互作用机制，是生物学领域的核心研究目标之一。种群间的遗传分化与表型分化，可由三类过程导致：一是种群间有限扩散与渐进式遗传漂变引发的距离隔离（isolation by distance）；二是定居历史与奠基者效应（founder effects）引发的定居隔离（isolation by colonisation）；三是适应不同环境阻碍种群间基因交流引发的适应性隔离（isolation by adaptation）。本研究以分布于三大大西洋群岛的特有雀形目鸟类——贝氏鹨（Anthus berthelotii）的岛屿种群为研究对象，尝试区分上述三类演化过程。研究借助微卫星标记与近似贝叶斯计算方法，揭示该物种约8500年前的北向定居事件致使其定居群岛出现遗传瓶颈现象。后续分析发现，群岛间存在显著的遗传结构，且该结构与定居隔离模式高度契合，而非距离隔离或适应性隔离模式。最后，本研究证实群岛间同样存在显著的表型分化，且该分化与遗传结构及瓶颈历史高度一致，但与环境差异或地理距离无明显关联。综合来看，本研究数据表明，奠基者效应是驱动各群岛间遗传与表型变异的核心因素。本研究结果为奠基者效应如何在演化时间尺度上持续发挥作用提供了罕见实证案例，并暗示其在物种形成早期阶段可能扮演重要角色。