Genome-wide genetic diversity of rove beetle populations along a metal pollution gradient

To what extent chemical contamination affects genetic diversity of wild populations remains an open question in ecotoxicology. Here we used a genome-wide approach (615 nuclear RADseq loci containing 3017 SNPs) and a mtDNA fragment (ATP6) to analyze the effect of long-term exposure to elevated concentrations of metals (Cd, Pb, Zn) on genetic diversity in rove beetle (Staphylinus erythropterus) populations living along a pollution gradient in Poland. In total, 96 individuals collected from six sites at increasing distance from the source of pollution were analyzed. We found weak differentiation between populations suggesting extensive gene flow. The highest genetic diversity was observed in a population inhabiting the polluted site with the highest metal availability. This may suggest increased mutation rates, possibly in relation to elevated oxidative stress levels. The polluted site could also act as an ecological sink receiving numerous migrants from neighboring populations. Despite higher genetic diversity at the most polluted site, there was no correlation between the genetic diversity and metal pollution or other soil properties. We did not find a clear genomic signature of local adaptation to metal pollution. Like in some other cases of metal tolerance in soil invertebrates, high mobility may counteract possible effects of local selective forces associated with soil pollution.