Landscape Genomic Analyses Reveal Rapid Adaptation to Climate in Introduced Biocontrol Weevils despite Multiple Founder Events

The distribution of many species are expected to shift markedly under future climate change scenarios, yet the capacity for populations to adapt to new climates is poorly understood. Introduced species offer excellent opportunities to explore the nature and sources of genetic variation that shape the ability of species to persist under new climates. The hairy weevil (Eustenopus villosus), a biocontrol insect for invasive yellow starthistle (Centaurea solstitialis), was introduced to the western US by a small number of founders from a single origin in its native range. Although populations successfully established, they have failed to control yellow starthistle, potentially because they lack genetic variation for adaptation to new climates. We identified and surveyed several thousand single nucleotide polymorphisms (SNPs) in hairy weevils using restriction site associated sequencing (RADseq). We compared genomic variation between native and introduced populations, and identified candidate loci underlying local adaptation to climate using regression-based models. We explored the putative function of loci associated with climate, and identified whether climatic adaptation in native and introduced populations has occurred at the same sets of marker loci. Our analyses revealed several candidate SNPs associated with precipitation and temperature in introduced weevils. Introduced populations have similar levels of genetic variation as their native origin, which implies a lack of genetic bottlenecks despite serial founder events. The results support rapid adaptation (less than 40 generations) to climate in small founding populations.