Niches and reproductive isolating mechanisms of two closely related species of New Zealand ground crickets (Orthoptera: Gryllidae, Nemobiinae)

Abstract

Comparative studies are made of the biology of Pteronemobius bigelowi Swan and the closely related and morphologically similar P. nigrovus Swan in order to investigate reproductive isolation between the two species. Their overlapping distributions are mapped for the North Island of New Zealand and Maori names for these and other crickets are discussed. Life cycles in the field are described for P. bigelowi, P. nigrovus, Teleogryllus commodus (Walker) (Gryllidae, Gryllinae), Metioche maoricum (Walker) (Gryllidae, Trigonidiinae), Conocephalus semivittatus (Walker) and C. bilineatus (Erichson) (Tettigoniidae) and Phaulacridium marginale (Walker) (Acrididae). At a coastal site where both species occur in close proximity, adults of P. bigelowi invaded areas which were occupied only by P. nigrovus earlier in the season. The factors which may determine the competitive success of either species in different habitats are discussed in relation to their distribution. The taxonomy of the genus Pteronemobius in New Zealand is considered with respect to the Australian species and recent revisions of the Nemobiinae. Methods are given for rearing P. bigelowi, P. nigrovus and T. commodus in the laboratory. The external morphology of the eggs of these three species is described. Hybrid eggs from reciprocal crosses between P. bige1owi and P. nigrovus resemble those of the maternal species in all respects. Virgin females of P. nigrovus and T. commodus lay infertile eggs, while those of P. bigelowi lay no eggs. The small numbers of eggs which were obtained in hybrid crosses between P. bigelowi and P. nigrovus were not viable. The behavioural effects of recordings of the male call and courtship songs were restricted to virgin conspecific females for P. bigelowi and to both virgin and mated conspecific females for P. nigrovus. This confirms McIntyre's hypothesis that the call song serves to maintain reproductive isolation and extends this finding to the courtship song.