How constrained is evolution? The importance of genetic redundancy in local adaptation

适应是进化的核心，但我们才刚刚开始回答关于它是如何工作的基本问题：物种以不同的方式适应同一种环境的情况有多普遍？为什么会出现这种情况？是什么维持了一个物种适应环境变化的能力？我的研究项目使用计算方法来探索遗传学如何影响进化的结果，然后试图用经验数据集来测试从这项工作中产生的假设，以回答这些基本问题。特别是，我的研究项目探讨了种群如何适应异质环境，在这种环境中，适应性权衡往往会阻止一种表型在所有可能的条件下都是最佳的。在这种情况下，不同的自然选择、迁移和重组之间的紧张关系可以极大地改变进化的遗传结构：在某些条件下，结构往往以更少、更大、更紧密聚集的等位基因为特征，而在其他条件下，它们往往以分布在整个基因组中的许多小等位基因为特征。这种生态学和遗传学之间的相互作用可以极大地影响进化的预测结果和可重复性，以及物种的可进化性。我建议探索基因型产生表型和表型转化为适合度的方式的差异如何影响局部适应的结构。我们将使用基于个体的模拟来探索基因型到表型映射中的冗余以及表型变化的有害副作用（即多效性）如何影响适应的结果，就进化的结构类型和适应的遗传基础的可重复性而言。这将为我们开发和扩展统计测试来比较不同物种适应类似压力的遗传结构提供理论基础。通过比较适应的遗传结构的相似性，我们将了解这些反应是由遗传约束还是选择约束形成的。最后，我们将收集两种鱼类（管状刺鱼和潮池刺鱼）对温度适应的新数据集，并将它们与现有的三刺棘鱼数据集进行比较，部署我们开发的测试来研究适应的可重复性。总的来说，这项研究将扩展对进化如何工作的理论理解，改进使用经验数据测试适应预测的统计工具，并提供一个案例研究，说明如何测试遗传学和生态学如何在基因组中形成适应模式。

Adaptation is central to evolution, but we are only beginning to answer fundamental questions about how it works: How commonly do species adapt to the same kind of environment in different ways? Why does this occur? What maintains the capacity of a species to adapt to changes in its environment? My research program uses computational approaches to explore how genetics can affect the outcome of evolution, and then seeks to test hypotheses that arise from this work using empirical datasets to answer these fundamental questions. In particular, my research program explores how populations adapt to heterogeneous environments, in which fitness trade-offs often prevent one phenotype from being optimal in all possible conditions. In such cases, the tension between divergent natural selection, migration, and recombination can greatly alter the genetic architecture that evolves: in some conditions, architectures tend to be characterized by fewer, larger, and more tightly clustered alleles, whereas in other conditions, they tend to be characterized by many small alleles distributed throughout the genome. This interplay between ecology and genetics can greatly affect the predicted outcome and repeatability of evolution, as well as the evolvability of a species. *** I propose to explore how differences in the way that genotypes give rise to phenotypes and phenotypes translate into fitness can affect the architecture of local adaptation. We will use individual-based simulations to explore how redundancy in the mapping of genotype to phenotype and deleterious side-effects of phenotypic changes (i.e. pleiotropy) affect the outcome of adaptation, in terms of the kind of architecture that evolves and the repeatability of the genetic basis of adaptation. This will provide the theoretical groundwork for us to develop and extend statistical tests to compare genetic architectures found in different species adapting to similar stresses. By comparing the similarity of genetic architectures underlying adaptation, we will learn whether such responses are shaped by genetic or selective constraints. Finally, we will collect novel datasets on adaptation to temperature in two species of fish: tubesnout and tidepool sculpin and compare them to existing datasets for threespine stickleback, deploying the tests we develop to study the repeatability of adaptation. Taken together, this research will extend theoretical understanding of how evolution works and improve statistical tools for testing predictions about adaptation using empirical data, as well as providing a case study illustrating how to test how genetics and ecology shape patterns of adaptation in the genome.