Centre for Invasion Biology, Department of Conservation Ecology and Entomology, Faculty of AgriSciences, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa.
J Insect Physiol. 2013 Aug;59(8):781-94. doi: 10.1016/j.jinsphys.2013.05.005. Epub 2013 May 15.
Fluctuating thermal regimes (FTR), consisting of cycles between stressful low and benign temperatures, are known to improve survival and fecundity in a variety of insects. By contrast, fluctuating hydration regimes (FHR) consisting of cycles between dehydrating and benign conditions have been less comprehensively researched. Hypothetically, either repeated stress accumulates damage and reduces survival, or the recovery periods may act as a protective mechanism by allowing low temperature- or dehydration-induced damage to be repaired. Using false codling moth (Thaumatotibia leucotreta) larvae, we investigated whether FTR and FHR resulted in protection, or accumulated damage, at the cellular and whole-organism levels. Time- and age-matched controls were used to verify that the effects were due to the fluctuating stressors and not age- or time-dependent responses. Results showed that larval body water-(BWC) and lipid content (BLC) remained unchanged in response to FTR. Importantly though, FTR are protective when compared to constant low temperature exposures, potentially due to an increase in heat shock protein 70 (HSP70). However, larvae may suffer long-term fitness consequences compared to constant benign exposures. Results for FHR appear equivocal when compared to constant controls, due to high survival rates for all experiments, although the physiological responses to FHR included a decrease in larval BWC and BLC, a decrease in cuticular water loss rates, and a depletion of HSP70 during the final dehydration cycle. In conclusion, it appears that fluctuating stressors are protective in T. leucotreta when compared to constant stress conditions, likely through regulation of whole-animal metabolic rate and HSP70, although other mechanisms (e.g. ion homeostasis) are also implicated.
波动热环境（FTR），由压力低和良性温度之间的循环组成，已知可以提高各种昆虫的存活率和繁殖力。相比之下，由脱水和良性条件之间的循环组成的波动水合环境（FHR）的研究则不那么全面。假设，反复的压力会积累损伤并降低存活率，或者恢复期可能通过允许低温或脱水引起的损伤得到修复而起到保护机制的作用。使用虚假苹果卷叶蛾（Thaumatotibia leucotreta）幼虫，我们研究了 FTR 和 FHR 是否会在细胞和整个生物体水平上导致保护或积累损伤。使用时间和年龄匹配的对照来验证这些影响是由于波动的应激源引起的，而不是与年龄或时间相关的反应。结果表明，幼虫的身体水分（BWC）和脂质含量（BLC）在响应 FTR 时保持不变。重要的是，与恒定低温暴露相比，FTR 具有保护作用，这可能是由于热休克蛋白 70（HSP70）的增加。然而，与恒定良性暴露相比，幼虫可能会遭受长期的适应性后果。与恒定对照相比，FHR 的结果似乎模棱两可，这是由于所有实验的存活率都很高，尽管对 FHR 的生理反应包括幼虫 BWC 和 BLC 减少、表皮水分损失率降低以及在最后一个脱水循环中 HSP70 耗尽。总之，与恒定应激条件相比，波动应激源似乎对 T. leucotreta 具有保护作用，这可能是通过调节整个动物的代谢率和 HSP70 实现的，尽管其他机制（例如离子稳态）也可能涉及其中。
