Genetics, variability and origin of tropical, subtropical and temperate life cycles in theDianemobius fascipesspecies‐complex (Orthoptera: Gryllidae)

Abstract

Egg diapause in the Nara (temperate, 34° 40'N) strain of Dianemobius nigrofasciatus of the D. fascipes species‐complex is programmed by the parental photoperiod and expressed as delayed hatching at a high temperature (25°C). However, very few delayed eggs occur at this or higher temperatures in the Bali (tropical, 8° 30'S) and Ishigaki (subtropical, 24° 20'N) strains of D. fascipes, though the subtropical strain shows a clearer incidence of diapause at 20°C. The results of crossing between the Nara and Bali or Ishigaki strains indicate no simple dominant‐recessive relations among alleles determining the incidence and intensity of diapause. Multiple regression analysis of F1, F2 and backcross eggs on mother and father for the incidence and intensity of diapause indicates additive effects of parental genes. A partial maternal effect was observed on the incidence, but not the intensity, of diapause. By artificial selection through several generations, lines with different diapause levels have been established from the subtropical strain, some of which are comparable to the temperate species in the intensity of egg diapause. A tropical strain of D. fascipes (Chiang Mai, 18° 30'N) showed an increased incidence and degree of hatching delay at a low temperature, suggesting the incipient form of a temperature‐dependent diapause. This might be the origin of egg diapause. Hatching delay was observed also in other tropical populations, and assumed to be preserved because of a bet‐hedging benefit in the unpredictably fluctuating tropical environment.