Male eyespan and resource ownership affect contest outcome in the stalk-eyed fly, Teleopsis dalmanni

The dominant theory for the evolution of male sexual ornaments is that they act as signals of male quality used by females in their mate choice. But these traits may also be used in male-male competition. In stalk-eyed flies, male eyespan (the distance between the eyes) is already known to play an important role in female mate choice. We investigated the influence of eyespan on male aggression over control of lek mating sites, both under controlled conditions and from field observations. Eyespan positively affected the number of aggressive encounters between two males on a lek. There were more aggressive interactions between large-eyespan males compared with small-eyespan males, and large-eyespan males won proportionately more aggressive interactions. Lek site ownership also influenced the outcome of aggression but to a smaller degree than eyespan. In addition, higher resource value, the number of females on a lek, increased the chance of aggression. The outcome of aggression between males is the control of lek aggregation sites, and this had direct consequences for male reproductive success, as lek owners gained more matings at both dusk and dawn. The importance of male-male competition in shaping sexual selection in stalk-eyed flies is discussed. (C) 2009 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.