Geographical variation in multiple paternity within natural populations ofthe guppy (Poecilia reticulata)

Mating can increase an individual's risk of mortality by predation. In resp onse to predation hazards, males in some species court females less often, but alternatively engage in coerced copulations more frequently and females become less selective. Such predator-mediated shifts in mating tactics may result in higher lea els of multiple inseminations in females and, thus, i n greater frequencies of females with broods of mixed paternity. We tested this hypothesis using two polymorphic microsatellite loci to estimate conse rvatively multiple paternity in broods of female guppies (Poecilia reticula ta) originating from ten natural populations that have evolved under differ ent fish predation regimes in Trinidad. The frequency of broods that were m ultiply sired was significantly greater on average in populations experienc ing high predation pressure compared to populations experiencing a relative ly low predation risk. These results suggest that the intensity of male spe rm competition covaries geographically with predation pressure in this spec ies and that the local risk of predation mediates the opportunity for sexua l selection within populations.