The effect of sperm production and mate availability on patterns of alternative mating tactics in the guppy

Theory predicts that in polyandrous species males that invest more in traits enhancing postcopulatory success should have less energy to invest in mating acquisition, leading to trade-offs between pre- and post-copulatory episodes of sexual selection. Although such trade-offs are well studied, the potential constraints that postcopulatory sexual selection imposes on alternative mating tactics are rarely considered. In guppies, Poecilia reticulata, individual males can obtain matings by performing energetically costly courtship displays or by using less costly forced copulations. In this study we manipulated a component of social environment (namely, the presence of females) to experimentally elevate sperm production in males. We found that male guppies rapidly compensated by reducing their reliance on courtship in favour of forced matings. As both tactics differ in mating and fertilization success, the consequences of this trade-off may have important ramifications for male reproductive fitness.