1 Department of Biology, Washington University in St. Louis, St. Louis, MO 63130; dan.g.bock@gmail.com losos@wustl.edu.
2 Functional Morphology Lab, Department of Biology, University of Antwerp, B-2610 Wilrijk, Belgium.
3 Department of Biological Sciences, University of Rhode Island, Kingston, RI 02881.
4 Department of Biology, Concordia University, Montreal, QC H4B 1R6, Canada.
5 Center for Population Biology and Department of Evolution and Ecology, University of California, Davis, CA 95616.
6 CREAF (Centre for Research on Ecology and Applied Forestry), Cerdanyola del Valles, Catalonia 08193, Spain.
7 Department of Genetics, University of Georgia, Athens, GA 30602.
8 Department of Biology and Center for Computational and Integrative Biology, Rutgers University, Camden, NJ 08102.
9 Living Earth Collaborative, Washington University in St

Hybridization is among the evolutionary mechanisms most frequently hypothesized to drive the success of invasive species, in part because hybrids are common in invasive populations. One explanation for this pattern is that biological invasions coincide with a change in selection pressures that limit hybridization in the native range. To investigate this possibility, we studied the introduction of the brown anole (Anolis sagrei) in the southeastern United States. We find that native populations are highly genetically structured. In contrast, all invasive populations show evidence of hybridization among native-range lineages. Temporal sampling in the invasive range spanning 15 y showed that invasive genetic structure has stabilized, indicating that large-scale contemporary gene flow is limited among invasive populations and that hybrid ancestry is maintained. Additionally, our results are consistent with hybrid persistence in invasive populations resulting from changes in natural selection that occurred during invasion. Specifically, we identify a large-effect X chromosome locus associated with variation in limb length, a well-known adaptive trait in anoles, and show that this locus is often under selection in the native range, but rarely so in the invasive range. Moreover, we find that the effect size of alleles at this locus on limb length is much reduced in hybrids among divergent lineages, consistent with epistatic interactions. Thus, in the native range, epistasis manifested in hybrids can strengthen extrinsic postmating isolation. Together, our findings show how a change in natural selection can contribute to an increase in hybridization in invasive populations.