Selection on size and secondary sexual characters of the damselfly Calopteryx splendens when sympatric with the congener Calopteryx virgo

Abstract

Male mating success is often determined by body size or secondary sexual characters because of female mate choice or competition for females. In addition to intraspecific interactions, interspecific interactions may interfere with intraspecific selection. In this study, we investigated sexual selection on size and sexual characters of male banded demoiselle ( Calopteryx splendens (Harris, 1780)) in wild populations sympatric with the beautiful demoiselle ( Calopteryx virgo (L., 1758)). As secondary sexual characters, male C. splendens have pigmented wing spots whose size appears to be under positive selection. Male C. virgo resemble male C. splendens that have the largest wing spots, leading to interspecific male–male aggression and possibly also to heterospecific matings via mistaken species recognition. If interspecific interactions interfere with intraspecific sexual selection on wing-spot size of C. splendens, their effects should increase with the increasing relative abundance of C. virgo. Our results did not show the expected positive selection on wing-spot size in C. splendens, suggesting that interspecific interactions might interfere with sexual selection. Also, we observed no relationship between the strength of interspecific sexual selection and the relative abundance of C. virgo. However, there was a positive intraspecific density-dependent sexual selection for larger size. Although the present results are tentative, we suggest that interspecific interactions should be considered along with intraspecific selection when studies of sexual selection are performed in the wild.