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

Abstract

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 affecting the willingness of males to mate in five species ofCoelopa:C.frigida, C.nebularum, C.ursina, C.pilipesandC.vanduzeei. The data from 2000 individual observations of pairs of flies revealed no association between female size and the willingness of males to mate, suggesting that males do not exhibit mate choice for larger, more fecund females. Male willingness to mount was associated with male size inC.frigida, C.nebularumandC.ursina, although not inC.pilipesandC.vanduzeei. There is considerable intraspecific variation in male size in the former three species, including the presence of two almost discrete size classes withinC.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 males are more active and thus likely to encounter and mount more females. In addition small males develop faster and thus gain earlier access to females.