SMALL MALES ARE MORE SYMMETRICAL - MATING SUCCESS IN THE MIDGE CHIRONOMUS-PLUMOSUS L (DIPTERA, CHIRONOMIDAE)

Male Chironomus plumosus most successful at acquiring mates showed lower levels of fluctuating asymmetry in length of wing than their rivals. These males were not of the most common size, but were the smallest in the population. These results are consistent with the prediction that where there is directional selection for small individuals, fluctuating asymmetry will be positively correlated with size. However, for a species that mates on the wing, selection may act upon symmetry per se rather than body size. Uncoupling the effects of size from those of asymmetry suggested that fluctuating asymmetry might, on its own, account for the observed mating success of C. plumosus. It is suggested that the success of the more symmetrical males is due to their improved aerobatic ability. Chironomus plumosus provides an example of the importance of fluctuating asymmetry in male characters that are not purely ornamental and these results are therefore more readily interpreted in terms of natural rather than sexual selection. (C) 1995 The Association For the Study of Animal Behaviour