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

Abstract

Male Tokunagayusurika akamusi chironomids have alternative mating tactics. One is to search for females on vegetation (ground mating), and the other is to wait for females in an aerial swarm (swarm mating). Simultaneous sampling of ground-unpaired and ground-paired males and of swarm-unpaired and swarm-paired males were performed. The average wing length and right-left wing length difference (wing asymmetry) were compared between males from the four different categories. Swarm-unpaired males were larger than ground-unpaired ones, swarm-paired males were larger than swarm-unpaired ones, and ground-paired males were not larger than ground-unpaired ones. Thus, large males tended to aggregate in swarms, and larger swarming males mated more successfully. On the other hand, small males probably enjoyed mating on the ground, especially when large males swarmed. The wing asymmetry was not significantly different between unpaired and paired males both within and between tactics. There was a flat or U-shaped relationship between wing length and asymmetry, underpinning the lack of a symmetrical advantage of swarming to large males. The right-left difference was not normally distributed in four of six samples of unpaired males but, in contrast, was not normally distributed in only one of six samples of paired males. The non-normal distributions were leptokurtic and included outliers. Removal of the outliers improved normality, suggesting that males with extremely asymmetric wings were not successful in mating.