Nonrandom variation in Poecilia marcellinoi n. sp. and P. salvatoris Regan, 1907 in El Salvador (Pisces, Poeciliidae)

A new species of the genus Poecilia Bloch & Schneider, 1801 is recorded from El Salvador. Morphological and meristic data of P. marcellinoi n. sp. and of the sympatric P. salvatoris Regan, 1907 are analysed. Intra- and interspecific variation are compared and correlated with environmental and interspecific influences. A high degree of character displacement is observed in populations from stable freshwater habitats. In habitats with presumed marine influences, this character displacement is counteracted by ecological stress. Based on the evidence presented, subspecific separation of observed ecotypes from literature is rejected.