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3rd Internat. Congr. Dipterology

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Pinnate scales on the legs and abdomen, enlarged wings, and eversible abdominal pleural sacs occur widely in various taxa of Empidinae. These features, which are restricted almost entirely to females, appear correlated with female swarming behavior. Previous hypotheses have proposed that all of these features evolved as aerodynamic adaptations to assist females with flight during swarming, or as precopulatory isolating mechanisms. However, the few detailed observations that are available for species with one or more of these features suggest that they are all signalling devices used by females as displays of fitness to compete for mates. Each feature appears to be an indicator of sex-role reversed courtship behavior, where females take an active role in courtship and males exhibit mate choice. Widespread sex-role reversed courtship behavior should be predicted by sexual selection theory for the Empidinae, because males generally monopolize the prey of females through transfers of nuptial gifts. Pinnate scales, enlarged wings, and eversible pleural sacs occur most commonly in females of the Empidini; for example they are found in over 28% of the 583 identified species of this tribe contained in the Canadian National Collection of Insects and Arachnids in Ottawa. The relatively extensive occurrence of these features throughout the Empidinae implies that sex-role reversed courtship behavior, in which mate choice has shifted from females to males, is probably a more significant evolutionary phenomenon for this group than has been previously recognized.

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