Size-dependent mate preference in the stalk-eyed fly Cyrtodiopsis dalmanni

We investigated size-dependent mate choice in the stalk-eyed fly Cyrtoniops is dalmanni. In this species, females prefer to mate with males with larger eyespans. We experimentally manipulated female eyespan by rearing larvae a t different densities. The mating preferences of females with small and lar ge eyespans were compared in choice chambers containing two males that diff ered in eyespan. Neither type of female distinguished between males with sm all differences in eyespan ((X) over bar =1.45 mm), but both preferred the male with the wider eyespan when the difference between males was large ((X ) over bar =3.17 mm). When presented with an intermediate difference in mal e eyespan ((X) over bar =2.40 mm), large-eyespan females showed a significa ntly stronger preference than small-eyespan females for the male with the w ider eyespan. Size-dependent mate choice in stalk-eyed flies is probably ca used by small-eyespan females being less able to discriminate differences b etween males. It may also reflect female condition, as eyespan is highly co rrelated with body size, which is a strong predictor of developmental condi tions. (C) 2001 The Association for the Study of Animal Behaviour.