Reproductive isolation in the wood cricket Gryllus vernalis (Orthoptera: Gryllidae)

Two species of closely related wood crickets, Gryllus vernalis (Orthoptera: Gryllidae) and G. fultoni, occur together in the eastern USA and have a similar calling-song structure, consisting of three-pulse chirps. Previous studies revealed that male calling song and female selectivity were divergent between sympatric and far allopatric populations of G. fultoni, consistent with the pattern expected of reproductive character displacement. We studied the reproductive isolation of G. vernalis in relation to G. fultoni by investigating the geographic variation in calling songs of G. vernalis and by examining close-range mating behaviors. Neither field nor laboratory studies revealed differences in any of the calling-song characters between sympatric and allopatric populations, but this could reflect the limited sampling within the relatively small region of allopatry for G. vernalis. Although close-range mating trials revealed that females of both species discriminated against heterospecific mating partners, the strength of discrimination was especially strong in females of sympatric G. vernalis populations. Our studies of long-range and close-range mating behaviors suggest that selection pressures for reproductive isolation are exerted primarily on close-range mating behaviors in G. vernalis but on long-range mating behaviors in G. fultoni.