Max Planck Institute for Demographic Research, Konrad Zuse Str. 1, 18057 Rostock, Germany.
Exp Gerontol. 2011 Oct;46(10):794-802. doi: 10.1016/j.exger.2011.06.004. Epub 2011 Jul 6.
Variation in life history can reflect genetic differences, and may be caused by environmental effects on phenotypes. Understanding how these two sources of life history variation interact to express an optimal allocation of resources in a changing environment is central to life history theory. This study addresses variation in the allocation of resources to asexual reproduction and to maintenance of Hydra magnipapillata in relation to differences in temperature and food availability. Hydra is a non-senescent, persistent species with primarily clonal reproduction. We recorded changes in budding rate and mean survival under starvation, which indicate changes in the allocation of resources to asexual reproduction and maintenance. In constant conditions we observed a clear trade-off between asexual reproduction and maintenance, where budding increased linearly with food intake while starvation survival stayed rather constant. In contrast, an environment with fluctuations in temperature or food availability promotes maintenance and increases the survival chances of hydra under starvation. Surprisingly, asexual reproduction also tends to be positively affected by fluctuating environmental conditions, which suggests that in this case there is no clear trade-off between asexual reproduction and maintenance in hydra. Environmental stresses have a beneficial impact on the fitness-related phenotypical traits of the basal metazoan hydra. The results indicate that, if the stress occurs in hormetic doses, variable stressful and fluctuating environments can be salutary for hydra. A closer examination of this dynamic can therefore enable us to develop a deeper understanding of the evolution of aging and longevity.
生活史的变化可以反映遗传差异，也可能是环境对表型的影响造成的。了解这两个生活史变异来源如何相互作用，以在不断变化的环境中最优地分配资源，是生活史理论的核心。本研究探讨了在温度和食物供应差异的情况下，水螅属(Hydra magnipapillata)无性繁殖和维持的资源分配的变化。水螅是一种非衰老、持久的物种，主要通过无性繁殖。我们记录了出芽率和饥饿状态下的平均存活率的变化，这表明了资源在无性繁殖和维持之间的分配发生了变化。在恒态条件下，我们观察到无性繁殖和维持之间存在明显的权衡关系，即出芽率随食物摄入线性增加，而饥饿存活率相对稳定。相比之下，温度或食物供应波动的环境促进了维持，并增加了水螅在饥饿状态下的生存机会。令人惊讶的是，无性繁殖也往往受到波动环境条件的积极影响，这表明在这种情况下，水螅的无性繁殖和维持之间没有明显的权衡关系。环境压力对基础后生动物水螅的与适应度相关的表型特征有有益的影响。研究结果表明，如果压力处于有益的剂量范围内，多变的压力和波动的环境对水螅可能是有益的。因此，更仔细地研究这种动态变化可以使我们更深入地了解衰老和长寿的进化。
