*School of Biological Sciences and the Center for Reproductive Biology, Washington State University, Box 664236, Pullman, WA 99164, USA; Department of Zoology, Center for Ecology, Southern Illinois University, Carbondale, IL 62901, USA.
Integr Comp Biol. 2013 Dec;53(6):989-1001. doi: 10.1093/icb/ict087. Epub 2013 Aug 5.
Exposure to adverse environmental conditions during early development can shape life-history traits and have lasting effects on physiological function in later life. Although findings within the biomedical literature have shown that environmentally induced elevations in glucocorticoids (GCs) during critical developmental windows can cause persistent carry-over effects (i.e., developmental programming), little is known about whether such effects of GCs can be generalized to wildlife species. Using wood frogs as a study species, we conducted an experiment with a split-plot design to assess the short-term and the long-term physiological consequences of availability of food, hydroperiod length (i.e., pond drying), and the interaction between these two environmental conditions. In outdoor experimental ponds, we reared tadpoles in chronically high or low-food conditions, and tadpoles from each pond experienced either high water until metamorphosis or a reduction in water volume during late developmental stages (after Gosner stage 38). After metamorphosis, animals were housed individually and fed ad libitum for 10 weeks, and growth rate, fat content, and resting and acute stress-induced GC levels were measured. We found that tadpoles experiencing low availability of food and reduced water volume had elevated GC levels, reduced mass, and body condition as they approached metamorphosis. At 10 weeks after metamorphosis, we found that these two conditions also had persistent interactive effects on post-metamorphic allocation of resources to growth, energy storage, and responsiveness of GCs to a novel stressor. Of individuals that experienced reduced water volume, only those that experienced high food as tadpoles were able to catch up to individuals that did not experience reduced water volume in terms of body mass, femur length, and body condition, and they allocated more resources to fat storage. By contrast, 10-week old frogs with low-food and that experienced low water volume and low-food levels as tadpoles allocated fewer resources to mass-specific growth, stored less fat, and exhibited blunted GC response to a novel stressor relative to those that did not experience water-reduction. Our findings demonstrate that environmental conditions experienced prior to and during important developmental transitions shape resource allocation and the ability to physiologically respond to future stressors in juvenile and potentially adult animals. These results suggest that chronic and acute environmental stressors experienced during early life stages can have cumulative and interactive effects that need to be considered when modeling the ecological and evolutionary consequences of environmental change on populations.
早期发育过程中暴露于不利环境条件会影响生命史特征，并对后期的生理功能产生持久影响。尽管生物医学文献中的研究结果表明，在关键发育窗口中环境诱导的糖皮质激素 (GCs) 升高会导致持续的传递效应（即发育编程），但对于 GC 是否可以推广到野生动物物种，知之甚少。我们使用林蛙作为研究物种，采用裂区设计进行了一项实验，以评估食物供应、水期长度（即池塘干涸）以及这两个环境条件之间的相互作用的短期和长期生理后果。在户外实验池塘中，我们在慢性高或低食物条件下饲养蝌蚪，并让每个池塘中的蝌蚪经历高水位直到变态，或在发育后期（Gosner 阶段 38 后）减少水位。变态后，动物被单独饲养并自由进食 10 周，测量生长速度、脂肪含量以及静息和急性应激诱导的 GC 水平。我们发现，经历低食物供应和减少水量的蝌蚪在接近变态时 GC 水平升高，体重和身体状况降低。在变态后 10 周，我们发现这两个条件对变态后资源分配到生长、能量储存以及 GC 对新应激源的反应也有持久的交互作用。在经历了减少水量的个体中，只有那些在蝌蚪期经历高食物的个体才能在体重、股骨长度和身体状况方面赶上没有经历减少水量的个体，并且它们将更多的资源分配到脂肪储存中。相比之下，10 周龄的青蛙，如果在蝌蚪期经历低食物和低水量以及低食物水平，则会减少特定体重的生长分配，储存较少的脂肪，并且对新应激源的 GC 反应减弱，与那些没有经历水减少的个体相比。我们的研究结果表明，在重要发育转变之前和期间经历的环境条件会影响资源分配和幼体以及潜在成年动物对未来应激源的生理反应能力。这些结果表明，在生命早期阶段经历的慢性和急性环境应激源可能会产生累积和交互作用，在模拟环境变化对种群的生态和进化后果时需要考虑这些作用。
