Molecular data provide strong evidence of natural hybridization between native and introduced lineages of Phragmites australis in North America

Hybridization, both within and between taxa, can be an important evolutionary stimulus for bioinvasions. Novel intra-taxon hybridizations may arise either between formerly allopatric introduced lineages, or between native and introduced lineages. The latter can occur following a cryptic invasion of a non-native lineage, such as the nineteenth century introduction to North America of a European lineage of the common reed Phragmites australis. Previous studies found no evidence of natural hybridization between native and introduced lineages of P. australis, but produced some F₁ hybrids under experimental conditions when the seed parent was native and the pollen parent was introduced. In this study we used microsatellite data to compare genotypes of P. australis along a transect of approximately 2,000 km in eastern North America. Although hybridization appears uncommon, simulations and principle component analysis of genetic data provided strong evidence for natural hybridization at two sites adjacent to Lake Erie in which native and introduced lineages were sympatric. The seed parent was the native lineage in some cases, and the introduced lineage in other cases. There is now the potential for P. australis hybrids to become increasingly invasive, and managers should consider as a priority the removal of introduced stands from sites where they co-exist with native stands.