How Repeatable is Adaptive Evolution? Testing What Promotes Rapid Adaptation in a Replicated Natural System

生物经常在环境中遇到巨大的压力，长期以来，在压力下的种群必须进化地适应、迁移或灭绝。对相同选择压力的独立适应为适应性进化的可重复性提供了令人信服的证据，但种群适应极端压力的速度有多快是一个有争议的问题。在这种情况下，促进反复快速进化的因素很难弄清，因为研究人员不太可能也很少能够观察到适应的最早阶段。突变并不经常发生，即使发生了也不太可能是有益的。我们的项目在夏威夷群岛的一个“自然实验室”中使用快速进化的蟋蟀（Teleogryllus oceanicus）来克服这些障碍。我们将通过测试最近的一种适应——雄性沉默——是如何以及为什么在致命的、偷听的寄生蝇的压力下独立地反复进化的，来评估快速适应的驱动因素。进化动力在适应的早期阶段可能会有所不同，蟋蟀系统是独一无二的，因为我们可以研究15年前才出现适应性变异的种群。此外，我们最近在地理上的种群马赛克中发现了沉默蟋蟀的多种变体，这使我们能够测试突变，迁移和选择如何相互作用以驱动重复的快速适应。该项目首先关注果蝇施加的选择，测量其强度和相关表型变异的地理格局，然后表征收敛突变体。它将所有进化过程纳入种群基因组学框架，通过模拟不同空间尺度（种群内、岛屿内种群间和群岛间）的选择性扫描，将迁移和选择结合起来。我们的研究结果将更清楚地了解限制或促进近期快速适应的因素，重要的是它们的相对作用以及它们如何相互作用。该项目将有助于解决关于引发快速适应所需的选择强度的争论，我们在这个系统中产生的关于选择、突变和迁移的基本信息将为其他系统的趋同进化和快速适应的一般过程提供信息。

Organisms often encounter dramatic pressures in their environment, and over the long term populations under pressure must evolutionarily adapt, migrate or go extinct. Independent adaptations to the same selection pressure provide compelling evidence for the repeatability of adaptive evolution, but how quickly populations can adapt to extreme pressure is a contentious issue. The factors that promote recurrent, rapid evolution in such cases can be difficult to disentangle because it is very unlikely and very rare for researchers to be able to observe the earliest stages of adaptation. Mutations do not occur frequently, and when they do they are not likely to be beneficial. Our project overcomes these obstacles using rapidly evolving crickets (Teleogryllus oceanicus) in a "natural laboratory" on the Hawaiian archipelago. We will evaluate the drivers of rapid adaptation by testing how and why a recent adaptation, male silence, has independently evolved repeatedly under pressure from deadly, eavesdropping parasitoid flies. Evolutionary dynamics can differ during the early stages of adaptation, and the cricket system is unique because we can study populations in which adaptive variants appeared only 15 years ago. In addition, we have recently discovered multiple variants of silent cricket in a geographic mosaic of populations, which allows us to test how mutation, migration, and selection interact to drive repeated rapid adaptation.The project first focuses on selection imposed by the flies, measuring its strength and the geographic pattern of associated phenotypic variation, then characterizes the convergent mutants. It joins all evolutionary processes in a population genomics framework, incorporating migration and selection by modelling selective sweeps at various spatial scales (within populations, across populations within islands, and across the archipelago). Our results will provide a clearer understanding of factors limiting or promoting recent, rapid adaptation, and importantly their relative roles and how they interact. The project will contribute to resolving debate over the strength of selection required to provoke rapid adaptation, and basic information we generate about selection, mutation and migration in this system will inform the general processes of convergent evolution and rapid adaptation in other systems.