European Dung-Fly Females All Aflutter for Large Males

ScienceDaily (Apr. 13, 2012) — European dung fly females prefer large males, making them the driving selective force behind the rare phenomenon in insects of large males and small females. This is what evolutionary ecologists from the University of Zurich discovered when they compared North American and European dung flies, which not only differ in sexual size dimorphism (SSD), but also in their mating behavior.

European and North American black scavenger flies -- also called dung flies as their larvae develop in the feces of vertebrates and thus break them down -- belong to the same species. Nevertheless, they strongly differ in mating behavior and SSD. North American dung fly females are larger than males, the usual dimorphism in insects. European dung flies, however, are more unusual with males being considerably larger than females. In evolutionary biology, sexual selection for large males can be explained if they can reproduce more successfully than smaller ones, either because females prefer larger males or because the latter prevail more often in the competition for mates with other males. Evolutionary ecologists from the University of Zurich showed that female preference for large males is far greater in European fly populations than in their North American counterparts, which explains the different SSD.

Continued:  http://www.sciencedaily.com/releases/2012/04/120413101112.htm