Sexual Selection on Male Morphology Independent of Male-Male Competition in the Mediterranean Fruit Fly (Diptera: Tephritidae)

Abstract

Sexual selection on morphology was examined in the lek-mating fly Ceratitis capitata (Weidemann). Single-pair courtships were videotaped in small chambers for males from a laboratory strain (L males) and males from the laboratory G2 generation of a sample of wild flies (W males). Virgin females derived from the wild population were used for all observations. The time spent on each courtship behavior (pheromone calling, wing fanning, wing buzzing, copulation attempt [mounting], missed jump during attempted copulation, and stationary status) was scored. Behavior was uncorrelated with morphology, except for a negative correlation between scutellum width and missed jump in L males. A multivariate analysis revealed that copulatory success is influenced by intermale variation to attempt copulation. Stabilizing sexual selection was apparent on eye length in L males and head width in W males, but size-related traits of thorax and wings had no effect on mating success. Because this selection was independent of any possible male-male competition, intersexual selection on male morphology is implied. Sexual selection on morphology was also substantial in a field cage experiment, where virgin flies were released into a cage containing a small host tree. The results of this caged experiment were consistent with those of single-pair courtships in that head morphology was suggested as a selection target, but directional selection (decreasing the trait mean) rather than stabilizing selection was apparent. Overall, male's head morphology was suggested to be at least one of the more probable direct target of mate choice of females once at a lek. The results are thus consistent with the predominant view that female mate choice is often significant in lek-mating systems.