INTERSPECIFIC HYBRIDS AND SPECIATION IN THE GENUS ACHETA (ORTHOPTERA, GRYLLIDAE)

Abstract

Acheta rubens produced interspecific hybrids with both the "northern spring species" (NSS) and assimilis in the laboratory, but not with pennsylvanicus; assimilis crossed with both rubens and pennsylvanicus but not with NSS; NSS crossed only with rubens; pennsylvanicus crossed only with assimilis. All other attempts to cross the four species failed. Over 2500 assimilis × rubens hybrids were produced within [Formula: see text] months; less than 1000 rubens × NSS hybrids were produced over about 18 months. The developmental rate of males carrying rubens X chromosomes was extremely slow in both rubens × assimilis and rubens × NSS hybrids; hybrid males carrying either assimilis or NSS X chromosomes, and all hybrid females, developed at normal rates, or at rates intermediate between those of the parental species. The songs of certain hybrid males were intermediate between those of the parental species in certain features but resembled the song of one parental species in other features. Fertile backcross males and females were produced by rubens × NSS hybrid females but the viability and fertility of the offspring of these specimens were abnormally low; both backcross and F2 nymphs have been produced by rubens × assimilis hybrids. The incubation periods of hybrid eggs laid by pennsylvanicus females were less than half those of normal pennsylvanicus eggs at the same temperature.