Understanding evolutionary dynamics of chromosomal inversions in adaption: the interplay of gene flux and selection

Objective

Understanding the genetic mechanisms that generate and preserve diversity is a central goal in biology. Chromosomal inversions, segments of a chromosome that are reversed in order, play a key role in the formation of locally adapted forms across a broad range of different species. They suppress recombination in heterozygotes, thereby maintaining large genomic blocks consisting of sets of locally adaptive alleles that can further diverge and evolve independently. Yet, exchange (‘gene flux’) between alternative arrangements can occur. It may be crucial for maintaining inversion polymorphisms and facilitating adaptation by reducing mutational load and generating novel allele combinations. However, the frequency of gene flux events, how they interact with selection, and their overall consequences for evolutionary dynamics and adaptation are still poorly understood. This project will investigate the frequency of gene flux events and their interplay with selection in a model system for adaptation, the threespine stickleback. In this ancestrally marine species, freshwater forms have independently evolved multiple times over very short timescales, despite ongoing gene flow from marine populations. Three ancient chromosomal inversions appear to play key roles in this process. However, in some freshwater systems, such as large lakes, the marine inversions persist, raising questions about their adaptive value in these environments. This project will use an ambitious multi-scale approach, from studying gene flux events in a single meiosis to large-scale global patterns to uncover the evolutionary dynamics of these special genomic regions and more generally advance our knowledge of the genetic architecture of adaptation.