Do male Trinidadian guppies adjust their alternative mating tactics in the presence of a rival male audience?

Males in polygamous mating systems may inadvertently transmit information regarding their mating preferences to bystanding sexual competitors, thereby permitting bystanders to use this information to enhance their own mating success by copying the mate choice of signallers. If males are at risk of having their mate choice copied and consequently face a higher risk of sexual competition, then selection should favour males that reduce conspicuous mating behaviours in the presence of an audience of sexual competitors. In the current study, we used the Trinidadian guppy (Poecilia reticulata), a species that exhibits alternative male mating tactics, to test this sexual competition avoidance hypothesis and the predictions that males would decrease their overall mating effort and exhibit fewer conspicuous courtship displays relative to more inconspicuous sneak mating attempts in the presence of either one or two sexual rivals compared to the absence of any audience. Male guppies significantly reduced their overall mating effort in the presence of increasing numbers of rival audience males. This was reflected in similar monotonic decreases in the frequencies of courtship displays and sneak mating attempts and in the proportional use of courtship displays (relative to sneak mating attempts) across treatments. These findings are consistent with the sexual competition avoidance hypothesis. Our novel results contribute to an increasing body of knowledge showing that the social environment can influence the mating effort and mating decisions of individuals and thus have important implications for sexual selection and evolution.