Fitness differences associated with calling behaviour in the two wing morphs of male sand crickets, Gryllus firmus

Alternate morphologies exist in a wide range of species. A commonly encountered dimorphism in insects is wing dimorphism, in which one morph is winged (macropterous=LW) and flight-capable while the other has reduced wings (micropterous=SW) and cannot fly. Gryllus firmus is a wing-dimorphic cricket found in the southeastern U.S.A. Although trade-offs associated with wing dimorphism are well established in female crickets, no such trade-offs have been demonstrated in male crickets. Differences between morphs in male G. firmus in the likelihood of attracting a female were tested in the laboratory using a simple T-maze where females chose between an LW male and an SW male. Time spent caling for each male was recorded on the sixth day of adult life. SW males were more likely to attract a female and spent more time calling than LW males. A logistic regression of female choice against the absolute proportional difference in calling time between males revealed that, as the difference in calling time between males increased, the likelihood of a female choosing the longer-calling male also increased. Therefore it is concluded that there is a trade-off between macroptery and the likelihood of attracting a female, and that it may be a primary factor in the maintenance of wing dimorphism in male G. firmus.