A trade-off between flight capability and reproduction in males of a wing-dimorphic insect

The widespread occurrence of dispersal polymorphisms among insects is consi stent with the hypothesis that fitness costs are associated with flight cap ability. Although trade-offs between flight capability and reproduction are well documented in the females of many wing-polymorphic insect species, th e relationship between dispersal capability and reproductive success in mal es is poorly established. Here we examine the potential cost of flight capa bility in males of the salt-marsh-inhabiting planthopper Prokelisia dolus ( Hemiptera: Delphacidae). This species exhibits a dispersal polymorphism wit h both flightless adults (brachypters) and migratory adults (macropters) oc curring in populations. In a competitive setting in the laboratory, brachypterous males exhibited a threefold mating advantage over macropterous males; they obtained 77% of t he matings with brachypterous females. This mating advantage resulted, in p art, from brachypterous males aggressively displacing rival macropters duri ng courtship. There was also a nonsignificant tendency for brachypterous ma les 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 con tested, the mating advantage of the male wing forms changed and macropterou s males obtained the majority of matings. Thus, there was evidence for asso rtative 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 bra chypters siring more offspring per female and not from inseminating more fe males; hence differences in sperm load between the male wing forms are impl icated in the siring advantage of brachypters. There was, however, no tende ncy for brachypterous males to survive longer than their macropterous count erparts; thus, differences in longevity did not contribute to enhanced siri ng ability. Overall, these results provide support for a trade-off between dispersal capability and reproductive success in males.