Weak Genetic Isolation and Putative Phenotypic Selection in the Wild Carnation Dianthus virgineus (Caryophyllaceae)

SIMPLE SUMMARY: Natural selection, genetic drift, and migration mainly drive evolution within species. By studying intraspecific variation at different elevations within the wild carnation Dianthus virgineus, we found a low genetic isolation paralleled by a high phenotypic differentiation among populations. In this species, genetic variation is related to geographic distance, whereas phenotypic variation does not result from genetic drift or gene flow limitations. Accordingly, we hypothesize that the phenotypic variation in this species is driven by selective forces, which act despite the presence of gene flow. ABSTRACT: By relating genetic divergence at neutral loci, phenotypic variation, and geographic and environmental distances, it is possible to dissect micro-evolutionary scenarios involving natural selection and neutral evolution. In this work, we tested the patterns of intraspecific genetic and phenotypic variation along an elevational gradient, using Dianthus virgineus as study system. We genotyped genome-wide SNPs through ddRAD sequencing and quantified phenotypic variation through multivariate morphological variation. We assessed patterns of variation by testing the statistical association between genetic, phenotypic, geographic, and elevational distances and explored the role of genetic drift and selection by comparing the Fst and Pst of morphometric traits. We revealed a weak genetic structure related to geographic distance among populations, but we excluded the predominant role of genetic drift acting on phenotypic traits. A high degree of phenotypic differentiation with respect to genetic divergence at neutral loci allowed us to hypothesize the effect of selection, putatively fuelled by changing conditions at different sites, on morphological traits. Thus, natural selection acting despite low genetic divergence at neutral loci can be hypothesized as a putative driver explaining the observed patterns of variation.