ena-STUDY-BOISE STATE UNIVERSITY-05-07-2019-15:09:49:472-440
The genetic architecture of hybrid fitness under environmental stress
Hybridization between species can either promote or impede adaptation. But there is a deficit in our understanding of the genetic basis of hybrid fitness, especially in non-domesticated organisms, and when populations are facing environmental stress. We made genetically variable F2 hybrid populations from two divergent Saccharomyces yeast species. We exposed populations to ten toxins and sequenced the most resilient hybrids on low coverage using ddRADseq to quantify three aspects of their genomes: 1) hybridity, 2) interspecific heterozygosity, and 3) epistasis (positive or negative associations between non-homologous chromosomes). We used linear mixed effect models and simulations to measure to which extent hybrid genome composition is contingent on the environment. We found strong genotype-by-environment interactions in every aspect of hybridness we measured. Individual chromosomes and chromosomal interactions revealed significant environment-dependent species biases. Our results suggest selection against heterozygosity, with larger fitness of genomes carrying more homozygous allelic combinations in an otherwise hybrid genomic background. We found no evidence for strong genetic incompatibilities, which is surprising given the large divergence of parental genomes (~15%). On the contrary, we observed beneficial, opposite-species associations between chromosomes, confirmed by epistasis- and selection-free computer simulations. Together, these results suggest that stress-resilient hybrid genomes can be assembled from the best features of both parents without paying high costs of negative epistasis. This illustrates the importance of measuring genetic trait architecture in an environmental context when determining the evolutionary potential of hybrid populations.
Hybridization between species can either promote or impede adaptation. But there is a deficit in our understanding of the genetic basis of hybrid fitness, especially in non-domesticated organisms, and when populations are facing environmental stress. We made genetically variable F2 hybrid populations from two divergent Saccharomyces yeast species. We exposed populations to ten toxins and sequenced the most resilient hybrids on low coverage using ddRADseq to quantify three aspects of their genomes: 1) hybridity, 2) interspecific heterozygosity, and 3) epistasis (positive or negative associations between non-homologous chromosomes). We used linear mixed effect models and simulations to measure to which extent hybrid genome composition is contingent on the environment. We found strong genotype-by-environment interactions in every aspect of hybridness we measured. Individual chromosomes and chromosomal interactions revealed significant environment-dependent species biases. Our results suggest selection against heterozygosity, with larger fitness of genomes carrying more homozygous allelic combinations in an otherwise hybrid genomic background. We found no evidence for strong genetic incompatibilities, which is surprising given the large divergence of parental genomes (~15%). On the contrary, we observed beneficial, opposite-species associations between chromosomes, confirmed by epistasis- and selection-free computer simulations. Together, these results suggest that stress-resilient hybrid genomes can be assembled from the best features of both parents without paying high costs of negative epistasis. This illustrates the importance of measuring genetic trait architecture in an environmental context when determining the evolutionary potential of hybrid populations.