SG: The adaptive (and maladaptive) consequences of non-additive genetic variation

Understanding the genetic basis, and potential limitations, of how organisms adapt to their environment is fundamentally important in many areas of biology. For example, such knowledge can improve crop breeding and can improve predictions about responses to climatic variability in both native and agronomic species. Current knowledge about the genetics of adaptation is mostly limited to a subset of genetic variation, where the effects of different copies (alleles) of a gene on survival and reproduction are additive and can simply be summed together. However, the effects of alleles on the organism can depend on the presence of other alleles for the same gene or different genes, and on environmental conditions. One example of this is called hybrid vigor, which often occurs when mating together plants of different strains, and results in hybrid offspring that have better survival and better seed production than either parent strain. The proposed research uses a unique set of genetic resources to quantify the contribution of these non-additive effects on survival and seed production. Outreach activities will be conducted with K-12 students on topics related to adaptation and maladaptation in the face of climate change. Despite nearly a century of work on the genetics of adaptation, we know little about the contribution of non-additive genetic variation to adaptation, the extent to which adaptation exists despite maladaptive loci, and how that balance may shift with environmental change. This research will determine the genetic basis of heterosis (hybrid vigor) and heterosis-by-environment interactions for fitness, quantify the role of epistasis in adaptive differentiation, and determine the extent to which antagonistic loci contribute to transgressive segregation in crosses between locally-adapted populations. Foundational work mapping the genetic basis of long-term fitness of two ecotypes of Arabidopsis thaliana from Italy and Sweden at the native sites implicated a complex genetic basis, including epistasis, a mixture of adaptive and maladaptive alleles, and transgressive segregation for fitness in Sweden. Dominance contributes to heterosis in a cross between these ecotypes, and limited genetic variation and high heterosis characterize northern populations. The research will leverage a panel of Near Isogenic Lines (NILs) to produce homozygous, heterozygous, and combinatorial introgression segments. To investigate heterosis, epistasis, and additive complementation for fitness, fitness components of these lines will be assayed in growth chambers programmed to simulate the native environments, designed and optimized with over a decade of site level climate and fitness data. Training will be provided for a graduate and undergraduate student who will also participate in K-12 outreach activities. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.