Mate choice, sexual coercion and gene flow in guppy populations

The role of behaviour in gene flow in Trinidadian guppies Poecilia reticulata was assessed using fish from an upstream and downstream pair of populations that differ in predation regime. High-predation (downstream) females preferred males from the corresponding low-predation population, but high-predation males achieved greater reproductive success under competition. This suggests that post-copulatory as well as pre-copulatory events are important in determining rates of gene flow.