Relationship Between Cold Stupor and Cold Tolerance inDrosophila(Diptera: Drosophilidae)

Abstract

Cold stupor (knock-down temperature) was studied in relation to cold tolerance (lethal temperature) in adult flies of cool-temperate, warm-temperate, and subtropical species belonging to the Drosophila melanogaster species group. Knock-down temperature was strongly correlated with lethal temperature ( r = 0.94). The cool-temperate species had lower knock-down and lethal temperatures, the subtropical species had higher ones, and the warm-temperate species had intermediate ones. Little intraspecific variation was observed in knock-down temperature. In a cool-temperate species, individuals in reproductive diapause had lower knock-down and lethal temperatures than reproducing ones. In addition, knock-down and lethal temperatures were lower in flies reared at a lower temperature. When rearing temperature was shifted, knock-down temperature changed with a logarithmic function of acclimation period. The rate of acclimation did not differ among the cool-temperate, warm-temperate, and subtropical species. Measurements on hybrids between D. lutescens Okada (a warm-temperate species) and D. takahashii Sturtevant (a subtropical species) suggested that loci responsible for the difference in knock-down temperatures between these 2 species were located on both autosome(s) and the X chromosome.