RT Journal Article SR Electronic T1 Hybridization and range expansion in tamarisk beetles (Diorhabda spp.) introduced to North America for classical biological control JF bioRxiv FD Cold Spring Harbor Laboratory SP 2021.05.18.444725 DO 10.1101/2021.05.18.444725 A1 Amanda R. Stahlke A1 Ellyn V. Bitume A1 A. Zeynep Ozsoy A1 Dan W. Bean A1 Anne Veillet A1 Meaghan I. Clark A1 Eliza I. Clark A1 Patrick Moran A1 Ruth A. Hufbauer A1 Paul A. Hohenlohe YR 2021 UL http://biorxiv.org/content/early/2021/05/18/2021.05.18.444725.abstract AB With the global rise of human-mediated translocations and invasions, it is critical to understand the genomic consequences of hybridization and mechanisms of range expansion. Conventional wisdom is that high genetic drift and loss of genetic diversity due to repeated founder effects will constrain introduced species. However, reduced genetic variation can be countered by behavioral aspects and admixture with other distinct populations. As planned invasions, classical biological control (biocontrol) agents present important opportunities to understand the mechanisms of establishment and spread in a novel environment. The ability of biocontrol agents to spread and adapt, and their effects on local ecosystems, depends on genomic variation and the consequences of admixture in novel environments. Here we use a biocontrol system to examine the genome-wide outcomes of introduction, spread, and hybridization in four cryptic species of a biocontrol agent, the tamarisk beetle (Diorhabda carinata, D. carinulata, D. elongata, and D. sublineata), introduced from six localities across Eurasia to control the invasive shrub tamarisk (Tamarix spp.) in western North America. We assembled a de novo draft reference genome and applied RADseq to over 500 individuals from laboratory cultures, the native ranges, and across the introduced range. Despite evidence of a substantial genetic bottleneck among D. carinulata in N. America, populations continue to establish and spread, possibly due to aggregation behavior. We found that D. carinata, D. elongata, and D. sublineata hybridize in the field to varying extents, with D. carinata x D. sublineata hybrids being the most abundant. Genetic diversity was greater at sites with hybrids, highlighting potential for increased ability to adapt and expand. Our results demonstrate the complex patterns of genomic variation that can result from introduction of multiple ecotypes or species for biocontrol, and the importance of understanding them to predict and manage the effects of biocontrol agents in novel ecosystems.Competing Interest StatementThe authors have declared no competing interest.