Female dimorphism and mating behaviour in a damselfly, Ischnura ramburi: females mimicking males

Females of the damselfly Ischnura ramburi exhibit a simple genetic colour dimorphism in which one form is cryptic (heteromorph), and the other closely resembles the more conspicuously colourful males (andromorph). Andromorphs also mimic male behaviour in interactions with males. Consequently they copulate half as often as do heteromorphs, which may give them a frequency-dependent selective advantage. Assuming that females need only mate once, excessive copulations, which average 3 h in duration, waste time for heteromorphs and may expose them to increased predation. The peculiar biology and mating behaviour of ischnurans provides a possible evolutionary context for this mimicry. The polymorphism is probably balanced by a frequency-independent selective disadvantage suffered by the more conspicuous andromorphs, through increased predation.