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。

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.