Male choice, willingness to mate and body size in seaweed flies (Diptera :Coelopidae)

The mating system of seaweed flies is characterized by scramble competition and a premating:struggle during which females vigorously attempt to remove mounted males and prevent copulation: Here we investigate factors affectin g the willingness of males to mate in five species of Coelopa: C. frigida, C. nebularum, C. ursina, C. pilipes and C. vanduzeei. The data from 2000 in dividual observations of pairs of flies revealed no association between fem ale size and the willingness of males to mate, suggesting that males do not exhibit mate choice for larger, more fecund females. Male willingness to m ount was associated with male size in C. frigida, C. nebularum and:C;ursina , although not in C. pilipes and C. vanduzeei. There is considerable intras pecific variation in;male size in the former three species, including the p resence of two almost discrete size classes within C, nebularum. We suggest that males of different sizes in these species may be adopting alternative reproductive strategies. Large males may benefit from increased longevity and their ability to withstand female rejection responses, whereas small ma les are more active and thus likely to encounter and mount more females. In addition small males develop faster and thus gain earlier access to female s. (C) 1999 The Association for the Study of Animal Behaviour.