Wave exposure as a driver of isolation by environment in the marine gastropod Nucella lapillus

Abstract

The way adaptive and neutral genetic variation is shaped by environmental factors is crucial for evolutionary biology. To investigate whether wave exposure can enhance local adaptation on littoral snails, AFLP markers were scanned across ten populations of Nucella lapillus from contrasting habitats (protected vs. exposed). As some 6% of the analysed loci deviated from neutral expectations, it was suggested that wave exposure could be a strong selective agent shaping genetic variation. Neutral markers described a pattern of “Isolation by distance (IBD) only” with no signature of Isolation by environment (IBE), whereas loci under divergent selection followed a pattern of “IBD and IBE”, as Partial Mantel tests detected a significant IBD after accounting for environmental differences. The topology of genetic networks revealed a substantial gene flow at neutral markers (i.e. dense net with edges connecting similar and contrasting habitats), whereas few connections were established between contrasting environments at loci under divergent selection. Furthermore, loci correlated to phenotype (shell shape; i.e. a morphological biomarker of wave exposure) explained up to ca 11% of the variance of this trait. Altogether, our results suggest that, even in a context of gene flow, local adaptation could outline a feature such as shell shape.