Institute for Zoology, University of Hamburg, Martin-Luther-King-Platz 3, Hamburg, 20146, Germany.
Department of Life Sciences, Hamburg University of Applied Sciences, Ulmenliet 20, Hamburg, 21033, Germany.
Integr Comp Biol. 2019 Jul 1;59(1):70-88. doi: 10.1093/icb/icz041.
Environmental change exposes wildlife to a wide array of environmental stressors that arise from both anthropogenic and natural sources. Many environmental stressors with the ability to alter endocrine function are known as endocrine disruptors, which may impair the hypothalamus-pituitary-thyroid axis resulting in physiological consequences to wildlife. In this study, we investigated how the alteration of thyroid hormone (TH) levels due to exposure to the environmentally relevant endocrine disruptor sodium perchlorate (SP; inhibitory) and exogenous L-thyroxin (T4; stimulatory) affects metabolic costs and energy allocation during and after metamorphosis in a common amphibian (Rana temporaria). We further tested for possible carry-over effects of endocrine disruption during larval stage on juvenile performance. Energy allocated to development was negatively related to metabolic rate and thus, tadpoles exposed to T4 could allocate 24% less energy to development during metamorphic climax than control animals. Therefore, the energy available for metamorphosis was reduced in tadpoles with increased TH level by exposure to T4. We suggest that differences in metabolic rate caused by altered TH levels during metamorphic climax and energy allocation to maintenance costs might have contributed to a reduced energetic efficiency in tadpoles with high TH levels. Differences in size and energetics persisted beyond the metamorphic boundary and impacted on juvenile performance. Performance differences are mainly related to strong size-effects, as altered TH levels by exposure to T4 and SP significantly affected growth and developmental rate. Nevertheless, we assume that juvenile performance is influenced by a size-independent effect of achieved TH. Energetic efficiency varied between treatments due to differences in size allocation of internal macronutrient stores. Altered TH levels as caused by several environmental stressors lead to persisting effects on metamorphic traits and energetics and, thus, caused carry-over effects on performance of froglets. We demonstrate the mechanisms through which alterations in abiotic and biotic environmental factors can alter phenotypes at metamorphosis and reduce lifetime fitness in these and likely other amphibians.
环境变化使野生动物暴露于大量人为和自然来源的环境胁迫因素中。许多能够改变内分泌功能的环境胁迫因素被称为内分泌干扰物，它们可能会损害下丘脑-垂体-甲状腺轴，从而对野生动物的生理产生影响。在这项研究中，我们研究了由于暴露于环境相关的内分泌干扰物高氯酸钠（SP；抑制性）和外源性 L-甲状腺素（T4；刺激性）而导致甲状腺激素（TH）水平改变如何影响常见两栖动物（Rana temporaria）在变态过程中和变态后的代谢成本和能量分配。我们进一步测试了幼虫阶段内分泌干扰的可能残留效应对幼体表现的影响。分配给发育的能量与代谢率呈负相关，因此，暴露于 T4 的蝌蚪在变态高峰期可比对照动物少分配 24%的能量用于发育。因此，暴露于 T4 导致 TH 水平升高的蝌蚪用于变态的能量减少。我们认为，由于变态高峰期 TH 水平改变和维持成本的能量分配导致代谢率不同，可能导致高 TH 水平的蝌蚪能量效率降低。大小和能量的差异持续到变态后，并影响幼体表现。表现差异主要与大小效应有关，因为暴露于 T4 和 SP 导致的 TH 水平改变显著影响了生长和发育速度。然而，我们假设，由于 T4 和 SP 暴露导致的 TH 水平改变会对生长和发育速度产生影响，因此幼体的表现受到独立于大小的 TH 实现的影响。由于内部宏营养素储存的大小分配存在差异，处理之间的能量效率也有所不同。由于几种环境胁迫因素导致的 TH 水平改变会对变态特征和能量产生持久影响，并因此对幼蛙的表现产生残留影响。我们证明了环境因素和生物因素的改变如何通过改变变态时的表型来降低这些和可能其他两栖动物的终生适应性。
