Sørensen Jesper Givskov, Kristensen Torsten Nygaard, Loeschcke Volker, Schou Mads Fristrup
Department of Bioscience, Aarhus University, Ny Munkegade 114, Building 1540, DK-8000 Aarhus C, Denmark.
Department of Biotechnology, Chemistry and Environmental Engineering, Section of Biology and Environmental Science, Aalborg University, Denmark.
J Insect Physiol. 2015 Jun;77:9-14. doi: 10.1016/j.jinsphys.2015.03.014. Epub 2015 Apr 4.
Coping with cold winter conditions is a major challenge for many insects. In early spring we observed newly emerged Drosophila subobscura, which had overwintered as larvae and pupae. As temperatures increase during spring these flies are faced with higher minimum and maximum temperatures in their natural microhabitat. Thus, there is a potential costly mismatch between winter and early spring acclimatization and the increased ambient temperatures later in adult life. We obtained individuals from a natural Danish population of D. subobscura and acclimated them in the laboratory to 20 °C for one generation, and compared critical thermal maximum (CTmax) and minimum (CTmin) to that of individuals collected directly from their natural microhabitat. The two populations (laboratory and field) were subsequently both held in the laboratory at 20 °C and tested for their CTmax and CTmin every third day for 28 days. At the first day of testing, field acclimatized D. subobscura had both higher heat and cold resistance compared to laboratory flies, and thereby a considerable larger thermal scope. Following transfer to the laboratory, cold and heat resistance of the field flies decreased over time relative to the laboratory flies. Despite the substantial decrease in thermal tolerances the thermal scope remained larger for field acclimatized individuals for the duration of the experiment. We conclude that flies acclimatized to their natural microhabitat had increased cold resistance, without a loss in heat tolerance. Thus while a negative correlation between cold and heat tolerance is typically observed in laboratory studies in Drosophila sp., this was not observed for field acclimatized D. subobscura in this study. We suggest that this is an adaptation to juvenile overwintering in temperate cold environments, where developmental (winter) temperatures can be much lower than temperatures experienced by reproducing adults after emergence (spring). The ability to gain cold tolerance through acclimatization without a parallel loss of heat tolerance affects thermal scope and suggests that high and low thermal tolerance act through mechanisms with different dynamics and reversibility.
应对寒冷的冬季条件对许多昆虫来说是一项重大挑战。早春时节，我们观察到了新羽化的暗果蝇，它们是以幼虫和蛹的形态越冬的。随着春季气温升高，这些果蝇在其自然微生境中面临着更高的最低和最高温度。因此，冬季和早春的适应性与成年后期环境温度升高之间可能存在代价高昂的不匹配。我们从丹麦暗果蝇的一个自然种群中获取个体，并在实验室中将它们在20°C的条件下驯化一代，然后将其临界热最大值（CTmax）和最小值（CTmin）与直接从其自然微生境中采集的个体进行比较。随后，这两个种群（实验室种群和野外种群）都被置于20°C的实验室环境中，并在28天内每隔三天对它们的CTmax和CTmin进行测试。在测试的第一天，与实验室果蝇相比，野外驯化的暗果蝇具有更高的耐热性和耐寒性，并因此具有相当大的热耐受范围。转移到实验室后，野外果蝇的耐寒性和耐热性相对于实验室果蝇随时间下降。尽管热耐受性大幅下降，但在实验期间，野外驯化个体的热耐受范围仍然更大。我们得出结论，适应其自然微生境的果蝇耐寒性增强，而耐热性并未丧失。因此，虽然在果蝇属的实验室研究中通常观察到耐寒性和耐热性之间存在负相关，但在本研究中，野外驯化的暗果蝇并未观察到这种情况。我们认为，这是对温带寒冷环境中幼虫越冬的一种适应，在这种环境中，发育（冬季）温度可能远低于羽化后繁殖成虫所经历的温度（春季）。通过适应获得耐寒性而不伴随耐热性的平行丧失的能力会影响热耐受范围，并表明高温和低温耐受性是通过具有不同动态和可逆性的机制起作用的。
