Polygenic selection within a single generation leads to subtle divergence among ecological niches

Moritz A Ehrlich, Dominique N Wagner, Marjorie F Oleksiak, Douglas L Crawford, Bonnie Fraser
2020 Genome Biology and Evolution  
Selection on standing genetic variation may be effective enough to allow for adaptation to distinct niche environments within a single generation. Minor allele frequency changes at multiple, redundant loci of small effect can produce remarkable phenotypic shifts. Yet, demonstrating rapid adaptation via polygenic selection in the wild remains challenging. Here we harness natural replicate populations that experience similar selection pressures and harbor high within-, yet negligible
more » ... ion genetic variation. Such populations can be found among the teleost Fundulus heteroclitus which inhabits marine estuaries characterized by high environmental heterogeneity. We identify 10,861 single nucleotide polymorphisms in F. heteroclitus that belong to a single, panmictic population yet reside in environmentally distinct niches (one coastal basin and three replicate tidal ponds). By sampling at two time-points within a single generation we quantify both allele frequency change within as well as spatial divergence among niche subpopulations. We observe few individually significant allele frequency changes yet find that the number of moderate changes exceeds the neutral expectation by 10-100%. We find allele frequency changes to be significantly concordant in both direction and magnitude among all niche subpopulations, suggestive of parallel selection. In addition, within-generation allele frequency changes generate subtle but significant divergence among niches, indicative of local adaptation. Although we cannot distinguish between selection and genotype-dependent migration as drivers of within-generation allele frequency changes, the trait/s determining fitness and/or migration likelihood appear to be polygenic. In heterogeneous environments, polygenic selection and polygenic, genotype-dependent migration offer conceivable mechanisms for within-generation, local adaptation to distinct niches.
doi:10.1093/gbe/evaa257 pmid:33313716 pmcid:PMC7875003 fatcat:3blathb3z5hilmm2nswhtfbnfe