From Pampas to Patagonia: Human-Modified Environments Drive the Spread of the Argentine Ant Beyond Its Climatic Limits

The Argentine ant (Linepithema humile) is a highly invasive species with a widespread global distribution. However, the dynamics of its recent expansion into southwestern Argentina remain unclear. We evaluated its spread, niche shifts, and genetic diversity using field surveys, distribution models, and mitochondrial DNA analyses. Our results revealed a strong expansion from Pampas into anthropogenic habitats (multiple urban and rural sites) in the Monte Desert, but not into natural habitats. The Argentine ant’s presence declined westward along the Río Negro Valley in the Monte Desert, and was virtually absent from the Patagonian Steppe, where it was found only in urban sites in Bariloche (ecotone with the Patagonian Forest). The distribution models identified isothermality and water balance as the key drivers of suitability. Thus, urbanization and irrigated agriculture seem to have facilitated its establishment in the Río Negro Valley by buffering climate extremes. Genetic analyses revealed widespread and novel haplotypes, which are consistent with multiple introductions and potential regional differentiation. This southward expansion underscores the critical role of urban areas and irrigated agriculture as refuges and stepping stones that facilitate Argentine ant survival in otherwise inhospitable environments. Continued monitoring of transitional zones in northern Patagonia is crucial to determining whether this front will remain stable or shift further south.