A TRADE-OFF BETWEEN FLIGHT CAPABILITY AND REPRODUCTION IN MALES OF A WING-DIMORPHIC INSECT

Abstract

The widespread occurrence of dispersal polymorphisms among insects is consistent with the hypothesis that fitness costs are associated with flight capability. Although trade-offs between flight capability and reproduction are well documented in the females of many wing-polymorphic insect species, the relationship between dispersal capability and reproductive success in males is poorly established. Here we examine the potential cost of flight capability in males of the salt-marsh-inhabiting planthopper Prokelisia dolus (Hemiptera: Delphacidae). This species exhibits a dispersal polymorphism with both flightless adults (brachypters) and migratory adults (macropters) occurring in populations. In a competitive setting in the laboratory, brachypterous males exhibited a threefold mating advantage over macropterous males; they obtained 77% of the matings with brachypterous females. This mating advantage resulted, in part, from brachypterous males aggressively displacing rival macropters during courtship. There was also a nonsignificant tendency for brachypterous males to arrive before macropterous males to court a calling female. Neither female rejection behavior nor male body size appeared to contribute to the mating advantage of brachypterous males. When macropterous females were contested, the mating advantage of the male wing forms changed and macropterous males obtained the majority of matings. Thus, there was evidence for assortative mating based on wing form. When placed with ten brachypterous females, brachypterous males sired twice as many offspring as did macropterous males. This advantage was due to brachypters siring more offspring per female and not from inseminating more females; hence differences in sperm load between the male wing forms are implicated in the siring advantage of brachypters. There was, however, no tendency for brachypterous males to survive longer than their macropterous counterparts; thus, differences in longevity did not contribute to enhanced siring ability. Overall, these results provide support for a trade-off between dispersal capability and reproductive success in males.