PARASITE LOAD, BODY SIZE, AND AGE OF WILD-CAUGHT MALE FIELD CRICKETS (ORTHOPTERA: GRYLLIDAE): EFFECTS ON SEXUAL SELECTION.

Comparison of male field crickets (Gryllus veletis and G. pennsylvanicus) collected either by themselves (solitary) or with one or more females (paired) showed that the paired males were significantly older and significantly less parasitized by gregarines (protozoan gut parasites) than were solitary males. Body size did not differ between the two groups. These results corroborate earlier experimental findings that females are preferentially attracted to older males and suggest that the ability of less parasitized males to produce more spermatophores under laboratory conditions may also be important in the field. Calculation of sexual-selection differentials and gradients for G. pennsylvanicus did not reveal any indirect selection on body size and confirmed the strong selection on male age. © 1988 The Society for the Study of Evolution.