Wing length and asymmetry of male Tokunagayusurika akamusi chironomid midges using alternative mating tactics

Male Tokunagayusurika akamusi chironomids have alternative mating tactics. One is to search for females on vegetation (ground mating), and the other i s to wait for females in an aerial swarm (swarm mating). Simultaneous sampl ing of ground-unpaired and ground-paired males and of swarm-unpaired and sw arum-paired males were performed. The average wing length and right-left wi ng length difference (wing asymmetry) were compared between males from the four different categories. Swarm-unpaired males were larger than ground-unp aired ones, swarm-paired males were larger than swarm-unpaired ones, and gr ound-paired males were not larger than ground-unpaired ones. Thus, large ma les tended to aggregate in swarms, and larger swarming males mated more suc cessfully. On the other hand, small males probably enjoyed mating on the gr ound, especially when large males swarmed. The wing asymmetry was not signi ficantly different between unpaired and paired males both within and betwee n tactics. There was a flat or U-shaped relationship between wing length an d asymmetry, underpinning the lack of a symmetrical advantage of swarming t o large males. The right-left difference was not normally distributed in fo ur of six samples of unpaired males but, in contrast, was not normally dist ributed in only one of six samples of paired males. The non-normal distribu tions were leptokurtic and included outliers. Removal of the outliers impro ved normality, suggesting that males with extremely asymmetric wings were n ot successful in mating.