Unexpected absence of behavioural differences between female damselfly colour morphs

Males are often selected for higher mating rates than females. As a consequence of this sexual conflict, unreceptive females may suffer fitness costs from excessive male sexual harassment. In a variety of vertebrate and invertebrate species, multiple female morphs coexist in natural populations which have been observed to differ in body colour, in behaviour and also in the amount of male harassment received. However, the degree of harassment on a female morph may depend on the frequency and density of males and female morphs in the population. We quantified harassment rate and subsequent refusal behaviour of males and female morphs of the polymorphic damselfly Nehalennia irene. Unexpectedly and contrary to previous work, female morphs received similar amounts of male harassment and showed mostly the same behaviour. We discuss why differences in morph behaviours may be lacking and how this compares to contemporary explanations for the maintenance and evolution of female-limited polymorphisms.