FLUCTUATING ASYMMETRY AND SEXUAL SELECTION IN THE MEDITERRANEAN FRUIT-FLY (DIPTERA, TEPHRITIDAE)

Sexual selection is known to operate at medfly leks with a few males g aining a high proportion of matings. However, specific male characteri stics subject to sexual selection have not been identified. Here we re port laboratory studies indicating that directional sexual selection o perates on the level of fluctuating asymmetry (FA) in the superior fro ntal orbital setae (sex setae), with symmetrical males gaining more ma tings. Studies relating mating success with FA in a male trait have ge nerally been taken as evidence of the operation of indirect sexual sel ection: For a male trait to acts as a reliable indicator of fitness, F A in the male trait should be negatively associated with trait size an d females should mate with the males with the most exaggerated form of the trait. However no association was found between seta FA and mean sera length. In addition sexual selection did not appear to operate on mean trait size, although males with an intermediate sex seta to wing length ratio did achieve higher mating success, indicating that stabi lizing sexual selection operates on this relative dimension. It is sug gested that differences in male competitive ability may provide an alt ernative explanation of how such associations between mating success a nd FA in male characteristics can arise. (C) 1998 The Linnean Society of London.