Gene flow and species delimitation

A defining feature of species is that their constituting populations are connected by gene flow. However, interspecific gene flow (introgression) can affect species integrity. If some genome components were less prone to introgression than others, they should be particularly suitable to delimitate species. Recent simulation studies have predicted a negative correlation between intra- and interspecific gene flow, suggesting that markers associated with the most dispersing sex should better delimitate species. A review of studies of introgression in species with sex-biased dispersal largely confirms this prediction. Hence, species delimitation should be more effective with markers experiencing high levels of gene flow, a simple but not widely appreciated prediction.