Absence of female conspecifics induces homosexual behaviour in male guppies

Social environment can have dramatic effects on the expression of speciestypical sexual behaviour. Using guppies, Poecilia reticulata, we asked how an all-male social environment affects male sexual behaviour. Males were assigned to either single-sex or mixed-sex groups. After 15 weeks, their sexual behaviour was assayed in the presence of three novel individuals of each sex. Males from single-sex groups performed higher rates of sexual displays and sneak copulation attempts towards stimulus males than did males from mixed-sex groups. Males from mixed-sex groups directed the majority of their sexual behaviour towards females using typical heterosexual behaviour. The social environment for each subject was then reversed for 2 weeks, after which subjects in both treatments showed a stronger tendency to display or sneak towards males. These findings reveal that homosexual behaviour is not readily extinguished when females become accessible and that it can be induced even after the ontogeny of heterosexual behaviour. While guppies may rarely occur in all-male groups in nature, these findings highlight the capacity for social environment to shape mating behaviour, which is particularly relevant for captive populations used in behavioural studies or conservation breeding programmes.