Reversible switches between male-male and male-female mating behaviour by male damselflies.

For many animal groups, both sexes have been reported to attempt to mate with members of their own sex. Such behaviour challenges theories of sexual selection, which predict optimization of reproductive success. We tested male mate choice between opposite- and same-sex members in the damselfly Ischnura elegans. Binary choice experiments were conducted following exposure periods in insectaries with only males or with both sexes present. We show that switches in choice between the opposite sex and the same sex can be induced and reversed again by changing the social context. We argue that the observed reversibility in male-male- and male-female-directed mating behaviour is maladaptive and a consequence of strong selection on a male's ability to alter choice between different female colour morphs.