荒漠昆虫光滑鳖甲的耐寒性季节变化及其生理机制

光滑鳖甲Anatolica polita borealis生活于温差大的新疆荒漠环境, 为探讨其耐寒性及耐寒机制, 本研究测定了其3-9月份成虫在－10℃的耐寒性、过冷却点（SCP）、含水量、甘油含量和血淋巴热滞活性(thermal hysteresis activity, THA)以及冷驯化对增强光滑鳖甲成虫耐寒性的效果, 还测定了光滑鳖甲不同发育阶段幼虫的SCP。结果表明: 光滑鳖甲成虫的耐寒性和SCP具有明显的季节性变化, 3月初SCP为－12.5℃, 7月为－6℃, 9月底为－13.6℃。4℃冷驯化能够提高光滑鳖甲成虫在－10℃的存活率, 未驯化组在40 min的存活率为50%, 而驯化2 h的为70%, 驯化24 h的为90%。虫体含水量在夏季有显著降低, 3月、7月和9月结合水与自由水的比值分别为10.8∶1,2.6∶1和5.4∶1。成虫甘油含量与SCP的回归方程为y=－0.6204x－5.681, R²=0.7714。成虫血淋巴THA与过冷却点的回归方程为y=－5.26x－1.713, R²=0.9049。血淋巴THA比甘油浓度更能影响过冷却点降低的程度。随着幼虫的发育, 其SCP逐渐降低。结果提示, 光滑鳖甲通过提高结合水与自由水的比值、增加抗冻蛋白和甘油的含量使虫体保持较低的SCP, 因而具有较高的耐寒性。

Seasonal changes in cold tolerance of desert beetle Anatolica polita borealis (Coleoptera:Tenebrionidae) and their physiological mechanisms

Anatolica polita borealis lives in desert environment where the temperature difference varies greatly in the year around. In order to explore the cold tolerance of the beetle and its possible mechanisms, changes in the supercooling point (SCP), body water content, glycerol content, and thermal hysteresis activity (THA) of hemolymph of the adults from March to September were assayed, and the effect of 4℃ cold acclimation on its cold tolerance were also evaluated. The SCP of the larvae at different developmental stages were determined. The results showed that the SCP of adult A. polita borealis changed apparently over seasons, being －12.5℃ in March, －6℃ in July and －13.6℃ in September. Cold acclimation at 4℃ for 2 h or 24 h enhanced the cold resistance of the adult beetles at －10℃ for 40 min, and the survival rates were 70% and 90%, respectively, while it was 50% in the non-acclimated group. Body water content significantly decreased in summer compared to those in spring and autumn. The ratio of bound water to free water in March, July and September were 10.8∶1, 2.6∶1 and 5.4∶1, respectively. The regression equation of the glycerol content and the SCP of the adult was y=－0.6204x－5.681, R²=0.7714, and that of the hemolymph THA and the SCP was y=－5.26x－1.713, R²=0.9049, showing that the hemolymph THA had more effect on the decrease of the SCP of the adult than the glycerol content did. The SCP of the larvae decreased with the larval development. The results suggest that A. polita borealis obtains high cold tolerance by keeping low SCP via increasing the ratio of bound water to free water and the amount of antifreeze protein and glycerol.