Biogeography of the Amazon molly, Poecilia formosa

Aim The unisexual Amazon molly (Poecilia formosa) is a clonal, all-female fish but depends on sperm of heterospecific males to trigger embryogenesis. Thus, one very important factor shaping its geographical range is the presence of suitable host males. Several species of the genus Poecilia from Central America, Mexico and the USA can provide sperm in the laboratory, but are not utilized as hosts in nature. Consequently the potential geographic range of the Amazon molly is much larger than the actual range. This raises the question of what is responsible for the biogeographical range of the Amazon molly? Location Southern USA, Mexico and Central America. Methods We review the current data available for the distribution of the Amazon molly. We further tested whether salinity might hinder the dispersal of the species. Results Amazon mollies tolerate marine conditions. We review the available data on recent and human influenced introductions of Amazon mollies. Main conclusions We argue that male preferences are not responsible for the current range. We propose that prevailing near-shore marine currents act as an effective barrier against further dispersal. Furthermore, we discuss recent changes in the biogeography of the Amazon molly.