Department of Hydrobiology, University of Warsaw, Banacha 2, 02-097 Warszawa, Poland.
J Insect Physiol. 2011 May;57(5):676-80. doi: 10.1016/j.jinsphys.2010.12.004. Epub 2010 Dec 15.
The effect of non-lethal thermal conditions on the diapause response to a simulated threat of fish predation was tested in the freshwater planktonic crustacean Daphnia magna. From an early developmental stage, female Daphnia were either exposed or not exposed to fish kairomones that notified of the threat of fish predation at the benign growth temperatures of 18, 22 or 26°C. The proportion of females switching from the production of subitaneous to diapausing eggs and their rate of reproduction were recorded. Besides the faster development and more intense reproduction observed at higher temperatures, a smaller proportion of the females formed protective, diapausing eggs when exposed to fish kairomones than was the case in colder conditions. The production of diapausing eggs was not observed when the threat of fish predation was absent. These results indicate an interactive effect of fish kairomones and thermal conditions on diapause induction in D. magna. We interpret these findings in the context of strategies for the maximisation of reproductive success. The production of well protected diapausing eggs (which assures low yet stable gains under diverse thermal conditions) may be a more beneficial life history strategy at lower temperatures, where the chances of survival of active individuals until maturation and successful reproduction are low. Higher temperatures permit faster maturation and more intensive reproduction that may surpass numerical losses of active descendants due to predation, making diapause a less rewarding option.
非致死热条件对模拟鱼类捕食威胁下滞育反应的影响在淡水浮游甲壳动物大型溞中进行了测试。从早期发育阶段开始，雌性大型溞要么暴露于鱼类信息素下，要么不暴露于鱼类信息素下，鱼类信息素通知了在 18、22 或 26°C 的良性生长温度下鱼类捕食的威胁。记录了从产生速生卵到滞育卵的雌性比例以及它们的繁殖速度。除了在较高温度下观察到更快的发育和更强烈的繁殖外，与在较冷条件下相比，暴露于鱼类信息素下的雌性形成保护性滞育卵的比例较小。当不存在鱼类捕食威胁时，不会观察到滞育卵的产生。这些结果表明鱼类信息素和热条件对大型溞滞育诱导的相互作用。我们根据最大化繁殖成功率的策略来解释这些发现。在较低温度下，产生保护良好的滞育卵（在各种热条件下保证低而稳定的收益）可能是一种更有益的生活史策略，因为活跃个体在成熟和成功繁殖之前存活的机会较低。较高的温度允许更快的成熟和更强烈的繁殖，这可能超过由于捕食而导致活跃后代的数量损失，使滞育成为一个不太有利的选择。
