The effect of visual obstructions on the sexual behaviour of guppies: the importance of privacy

Sexual selection is the outcome of behavioural interactions within and between the sexes. Numerous studies show how individuals modify their sexual behaviour in response to ecological or social conditions, and such changes may therefore affect the evolutionary outcome of sexual selection. Our study examined the effect of habitat structure on the sexual behaviour of male and female guppies, Poecilia reticulata. We asked whether the ability of males to observe other courting males would affect the rates of male courtship and courtship interference and the sexual responsiveness of females. Specifically, we manipulated visibility using opaque barriers in laboratory aquaria and found that there was less male interference behaviour in aquaria containing visual obstructions than in aquaria without barriers, regardless of whether the male was courting sexually responsive (virgin) or unresponsive (nonvirgin) females. In addition, sexual responsiveness of virgin females to male displays was significantly increased in aquaria with barriers relative to aquaria without barriers. Finally, the display frequency of males courting virgin females was significantly reduced in aquaria with barriers, probably as a result of the females' increased rate of sexual response. Evidently, the barriers impede visibility enough that males are less likely to observe and interfere with the courtship of other males, and therefore, females are less likely to flee or lose interest in a courting male. Ultimately, characteristics of the visual environment could affect females' ability to choose mates and in turn could potentially affect the evolutionary outcome of sexual selection.