THE EVOLUTION OF ALTERNATE MORPHOLOGIES - FITNESS AND WING MORPHOLOGYIN MALE SAND CRICKETS

Many organisms show distinct morphological types. We argue that the ev olution of these alternate morphologies depends upon both fitness diff erences between morphs within each sex and the genetic correlation bet ween sexes. In this paper, we examine the evolution of alternate morph ologies using wing dimorphism in insects as a model system. Many insec t species are wing dimorphic, one morph having wings and being capable of flight, the other lacking functional wings. While there is a well established trade-off in females between macroptery and reproduction, there are few data on the possible costs in males. We examine trade-of fs between macroptery and life-history traits in male sand crickets, G ryllus firmus, and estimate the genetic correlation of wing dimorphism between the sexes. Macropterous males develop faster than micropterou s males and are either larger or the same size depending upon rearing conditions. There is no difference in absolute or relative testis size at eclosion or 7 d thereafter. Finally, there is no difference betwee n macropterous and micropterous males in relative success at siring of fspring. Thus, with respect to the above traits, there are no costs as sociated with being winged in male G. firmus. It is possible that ther e may be a trade-off between calling rate and macroptery. A comparison of the relative frequency of macroptery between males and female acro ss different orders of insects supports this hypothesis. The genetic c orrelation of wing dimorphism between the sexes is high (r(8) = 0.86), and hence the frequency of macroptery in males may be strongly influe nced by selection acting on females.