Effect of starvation on the cold tolerance of adult Drosophila suzukii (Diptera: Drosophilidae)

The spotted wing drosophila, Drosophila suzukii, is an invasive pest in Europe and North America. Access to resources may be challenging in late fall, winter and early spring and flies may suffer from food deprivation along with cold stress in these periods. Whereas a plethora of studies have been performed on the overwintering capacity of D. suzukii, the effects of starvation on the fly's cold tolerance have not been addressed. In the present study, young D. suzukii adults (reared at 25°C, LD 12:12 h) were deprived of food for various periods (0, 12, 24 and 36 h), after which chill coma recovery time, critical thermal minimum, as well as acute and chronic cold tolerance were assessed. Additionally, the body composition of adults (body mass, water content, total lipid, glycerol, triglycerides, glucose and proteins) before and after starvation periods was analysed to confirm that starvation had detectable effects. Starved adults had a lower body mass, and both lipid and carbohydrate levels decreased with starvation time. Starvation slightly increased critical thermal minimum and affected chill coma recovery time; however, these changes were not gradual with starvation duration. Starvation promoted acute cold tolerance in both sexes. This effect appeared faster in males than in females. Food deprivation also led to enhanced survival to chronic cold stress. Short-term starvation was thus associated with significant changes in body composition in D. suzukii, and these alterations could alter some ecologically relevant traits related to cold tolerance, particularly in females. Our results suggest that food deprivation during short time (<36 h) can promote cold tolerance (especially survival after a cold stress) of D. suzukii flies. Future studies should address the ecological significance of these findings as short food deprivation may occur in the fields on many occasions and seasons.

Acclimatory responses of thermal physiological performances in hatchling yellow pond turtles (Mauremys mutica)

Temperature is a crucial environmental factor that can strongly impact animal physiology. Here, we acclimated hatchling of Asian yellow pond turtles (Mauremys mutica) to one of two different temperatures (25 or 30°C) for four weeks to determine temperature acclimation effects on their physiology. All four measured physiological variables (righting time, resting metabolic rate, critical thermal minimum and critical thermal maximum) were significantly affected by temperature acclimation. Turtles acclimated to 25°C righted themselves more slowly and had a lower mean metabolic rate than 30°C-acclimated turtles. Turtles acclimated to 25°C were more resistant to low temperatures, but less resistant to high temperatures than 30°C-acclimated turtles, as measured by critical thermal limits. The thermal resistance range (i.e., the difference between critical thermal minimum and maximum) did not differ between the two acclimation groups. Compared with other semi-aquatic turtles, M. mutica had relatively higher acclimation response ratios for its critical thermal minimum and critical thermal maximum. Our results indicate that acclimation to relatively moderate temperatures could also produce significant responses in the thermal physiology of turtles.