Chemical control is a common strategy for managing invasive species. However, invasive species may evolve resistance to these chemicals, resulting in substantial economic, societal, and environmental losses. As an invasive species in the Great Lakes, sea lamprey (Petromyzon marinus) have been treated with the lampricide, 3-trifluoromethyl-4-nitrophenol (TFM), for ~60 years. In order to test whether sea lamprey are developing resistance to TFM, we collected sea lamprey larvae from Lake Michigan (LM, TFM treatment for ~60 years), Lake Champlain (LC, TFM treatment for ~30 years) and the Connecticut River (CT, no TFM treatment). After a lengthy acclimation period, we exposed the larvae to TFM at concentrations of 0 mg/L (control), 2 mg/L and 3 mg/L, from which we sampled muscle tissues to generate RNA sequencing (RNA-seq) data. With the RNA-seq data, we identified differentially expressed genes, called SNPs, calculated measures of genetic diversity, and tested for evidence of loci under selection.
Results/Conclusions
We called 53,579 SNPs for 44 sea lamprey (LM: n=17; LC: n=13; CT: n=14). Observed heterozygosity of three populations show a consistent pattern, with the highest genetic diversity observed in the Lake Michigan population and the lowest genetic diversity observed in the Lake Champlain population. According to FST outlier tests, 48 loci show evidence of adaptive differences among populations. Outlier loci provide evidence for differential responses to TFM in sea lamprey across varying degrees of TFM exposure, suggesting an adaptive response to TFM. Our next steps are to uncover mechanisms at the genomic level by studying candidate loci and genes. Combined with patterns of differential gene expression, these analyses suggest that invasive sea lamprey may be in the early stages of developing resistance to their only known pesticide.