Too much water under the bridge: Unraveling the worldwide invasion of the tree tobacco through genetic and ecological approaches

Abstract

Understanding how, and from where, invasive species were introduced is critical for revealing the invasive mechanism, explaining the invasion success, and providing crucial insights for effective management. Here, we combined a phylogeographic approach with ecological niche modeling comparisons to elucidate the introduction mode and source of Nicotiana glauca, a native South American species that is now invasive worldwide. We tested three different scenarios based on the invasion source—random native, restricted native, and bridgehead invasive—considering genetic diversity and climatic niche comparisons among native and invaded areas. We found three genetic lineages geographically and climatically differentiated within the native range. Only one of these genetic groups contained the invasive haplotypes, but showed no climatic niche overlap with any invaded area. Conversely, one invaded area located in western South America, with more genetic diversity than other invaded areas but less than the native range, showed climatic niche overlap with almost all other invaded areas worldwide. These findings indicate that N. glauca first likely invaded the southernmost areas beyond its native range, forming a bridgehead invasive source, from which the species subsequently invaded other regions around the world. Invasiveness would have been fostered by changes in the environmental preferences of the species in the bridgehead area, towards drier, colder and less seasonal climates, becoming the actual source of invasion to areas climatically similar throughout the world. The fine scale resolution analyses combining genetic and climatic approaches within the native range were essential to illuminating the introduction scenario of this invasive species.