Size or symmetry: an experiment to determine which of the two accounts for mating success in male midges

It has repeatedly been demonstrated that size, or its correlates, determine the mating success of male animals. Recently a second character, fluctuating asymmetry, has been identified as important in this regard. Thus, there may be two components to success for the male, size and symmetry. The question is the relative importance of the two. Here an experiment is described, designed to address this question. The midge Chironomus plumosus L. is the test organism. Swarms of males in the wild were manipulated to increase the average wing asymmetry of the swarm. An unmanipulated swarm provided a control. By this means the effects of size and fluctuating asymmetry were uncoupled. The outcome is that symmetry alone appears sufficient to account for mating success among males of this midge.