GENETIC DIVERGENCE, FEMALE CHOICE AND MALE MATING SUCCESS IN TRINIDADIAN GUPPIES

Guppy, Poecilia reticulata, populations from two major Trinidadian dra inages, the Caroni and Oropuche, are characterised by high levels of g enetic divergence. Our aim in this paper was to determine whether this divergence is linked to behaviourally-based reproductive isolation. W e compared two populations of guppies, one from the Tacarigua River in the Caroni drainage, the other from the Oropuche River in the Oropuch e drainage. Guppies in both sites are subject to predation from the pi ke cichlid, Crenicichla alta, and other predators. In visual choice te sts, virgin females from both the Oropuche and Tacarigua populations s howed no preference for either type of male. This result was confirmed when females had free access to males. However, a population asymmetr y in male mating behaviour resulted in Tacarigua males gaining virtual ly all copulations. We argue that predation risk has constrained femal e choice and discuss the evolutionary significance of population diffe rences in male behaviour.