Courtship role reversal and deceptive signals in the long-tailed dance fly, Rhamphomyia longicauda.

We examined the function of secondary sexual characters in the role-reversed, lekking behaviour of female long-tailed dance flies, Rhamphomyia longicauda Loew (Empididae), to test the hypothesis that the degree of abdominal distention is an honest female signal about the state of egg development. Female Rhamphomyia cannot hunt for prey and they receive all of their protein from males by exchanging copulations for nuptial prey gifts. Females compete for male gifts within leks that are organized for a brief period each evening before dark. Before hovering within leks, females swallow air, inflating expandable pouches on the pleural margins of the abdomen. The result is a large saucer-like abdomen which is further exaggerated by wrapping scaled pro-, meso- and metathoracic legs along its pleural margins. Male preference for an enlarged abdomen was confirmed by suspending plastic models of varying size from monofilament lines and recording which models attracted the most males. There was a positive relationship between egg development and abdominal distention in a related species, R. sociabilis (Williston), which lacks inflatable abdominal pouches. Multiple regression showed that in R. longicauda, abdominal inflation completely masks the state of egg development. We conclude that female R. longicauda deceive mate-seeking males with the unreliable message that eggs are nearing maturation in order to obtain a protein meal in exchange for copulation. Males that fail to identify a female bearing mature eggs risk near-certain cuckoldry and an increased probability that the female will die before oviposition. Copyright 2000 The Association for the Study of Animal Behaviour.