Climate‐Associated Genetic Variation in Native and Introduced Populations of Eustenopus villosus , a Biological Control Agent for Yellow Starthistle

ABSTRACT

Contemporary evolution in biological control systems is rarely studied, though biological agents are repeatedly exposed to novel environmental conditions upon introduction. Their ability to adapt to new conditions could influence management efficacy and reveal important aspects of environmental selection. Using a ddRADseq dataset, we tested for genomic evidence of adaptation to climate in populations of Eustenopus villosus (Boheman, Coleoptera: Curculionidae), the “hairy weevil”, which is used in classical biological control for yellow starthistle ( Centaurea solstitialis L., Asteraceae) in the western United States. We first estimated population structure in E. villosus across our samples of the native and introduced ranges and then used six complementary genotype‐environment association analyses to identify single nucleotide polymorphisms (SNPs) associated with climate in both native and introduced populations. Additionally, we used historical release records to categorize sampling sites according to their serial founding history and test for impacts of this history on total and putatively adaptive genomic variation in the introductions. We also tested whether candidate loci associated with climate in the native range exhibit similar associations in the introductions, or if new associations have evolved. We identified many candidate loci in both native and introduced populations and found little evidence of a decline in genomic variation, which suggests that serial founding events did not prevent climatic adaptation. Candidate loci differed between native and introduced populations, indicating that local adaptation has occurred in different regions of the genome after introduction of E. villosus . Our findings suggest an important role for novel contemporary adaptation in this biological control system and provide insight into how genetic variation can persist in biological control agents through introduction and serial founding events.