Genetic Divergence, Female Choice and Male Mating Success in Trinidadian Guppies

Guppy, Poecilia reticulata, populations from two major Trinidadian drainages, the Caroni and Oropuche, are characterised by high levels of genetic divergence. Our aim in this paper was to determine whether this divergence is linked to behaviourally-based reproductive isolation. We compared two populations of guppies, one from the Tacarigua River in the Caroni drainage, the other from the Oropuche River in the Oropuche drainage. Guppies in both sites are subject to predation from the pike cichlid, Crenicichla alta, and other predators. In visual choice tests, virgin females from both the Oropuche and Tacarigua populations showed no preference for either type of male. This result was confirmed when females had free access to males. However, a population asymmetry in male mating behaviour resulted in Tacarigua males gaining virtually all copulations. We argue that predation risk has constrained female choice and discuss the evolutionary significance of population differences in male behaviour.