Low temperature tolerance of insects in relation to the influence of temperature on muscle apyrase activity

Abstract

The influence of temperature on the rate of apyrase activity was examined in species that differ in chill-coma and habitat temperatures. Correlations were sought which might account for the ability of some insects to remain at temperatures causing inactivation or chill-coma in other species. Muscle apyrase determinations were made with the housefly, Musca domestica; the sarcophagid fly, Sarcophaga bullata; the waxmoth, Galleria mellonella; the giant death's head roach, Blaberus craniifer; warm-, cold-, and unadapted American cockroaches, Periplaneta americana; warm- and cold-adapted mealworms, Tenebrio molitor; the crayfish, Cambarus diogenes; and the horseshoe crab, Limulus polyphemus. At given low temperatures the rates and temperature coefficients of apyrase activity were generally higher in animals with the lower chill-coma temperatures. However, at temperatures 3–4°C above the respective chill-coma temperatures, the rates were nearly the same in each species (0·4±0·1 μg P/mg muscle/min). The relationship between chill-coma temperature and temperature coefficient was linear; in the insects, 1°C difference in coma temperature was equivalent to a difference of about 2400 cal in μ-value. Apyrase rate maxima occurred at lower temperatures in species having lower chill-coma temperatures, and the maxima were greater in species that might be regarded as normally most active. In an intraspecific comparison apyrase activity at given temperatures was greater in cold-adapted than in warm-adapted P. americana. However, intraspecific adaptation appeared to have little or no effect on the temperature coefficients of apyrase activity. It was concluded that (1) higher apyrase rates, (2) higher temperature coefficients in species with lower chill-coma temperatures, and (3) the occurrence of a common rate of apyrase activity at a temperature several degrees above the respective chill-coma temperatures might well constitute important mechanisms involved in the adaptive compensation permitting maintenance of activity at low temperatures. The data are consistent with the suggestion that perhaps a minimum rate of hydrolysis of ATP is necessary to permit muscular contraction.