Conditional expression of a sexually selected trait in the stalk-eyed fly Diasemopsis aethiopica

1. An important assumption of many models of the evolution of sexually sele cted ornaments is that such ornaments should be conditionally expressed. Th is was investigated by rearing larvae of the stalk-eyed fly Diasemopsis aet hiopica (Diptera: Diopsidae) (Rondani) on two food treatments: normal and l ow-quality food. 2, Female flies responded to better food by increasing both their body size and the relative length of their eyestalks. 3. Male flies responded by increasing only the length of their eyestalks. 4. This demonstrates that food quality can change the allometric relationsh ip between body size and the size of a sexually selected character in this species, and gives an insight into the different developmental priorities o f each sex in this species.