Complex range expansion and selective regime in the introduced Florida cane toad.

Introduced species that successfully establish in new areas are a powerful system for investigating the genetic, ecological, and adaptive processes underlying range expansion. Rhinella marina is the focus of many studies of invasion dynamics, rapid evolution, and range limits. However, comparatively little is known about the nearly simultaneous establishment of closely related R. horribilis in Florida, USA. We sequenced 280 individuals using double-digest restriction-associated DNAseq (ddRAD) to investigate the role of introduction history, standing genetic diversity, and adaptation in R. horribilis' establishment in Florida. We test the hypothesis of a single introduction event versus the alternative of several cryptic introductions. Second, we characterize population structure and genetic diversity to elucidate the roles of genetic bottlenecks and subsequent gene flow. Third, we use redundancy analyses to identify climate-associated genetic variants that may play a role in adaptation in Florida, which is colder than the cane toad's native range. Lastly, we analyze a morphological trait, limb length, to investigate potential evolution of dispersal at the range edge. We find evidence for a single introduction of R. horribilis and complex range expansion characterized by range-wide gene flow, a lack of isolation by distance or environment, and no range edge dispersal phenotype. We also find evidence of selection related to range-wide gradients of precipitation, temperature, and urbanization. Together, our results indicate that range-wide gene flow maintains genetic diversity and adaptive capacity, likely supporting the neotropical species' success in adapting to and establishing in this temperate environment.