CRB: Role of Immune Function and Disease in Amphibian Disappearances

最近关于世界范围内两栖动物数量下降和灭绝的报告提出了环境变化与某些两栖动物物种灭绝之间关系的问题。如果这些物种受到人为变化的伤害，两栖动物可能被证明是极好的“衰退的先兆”和生态系统压力的指示器。两栖动物数量下降的原因还没有得到确凿的证明。下面的工作假设被提出来解释环境变化如何可能导致两栖动物种群的灭绝。1. 在这些两栖动物的环境中，一个因素的亚致死变化，或几个因素的多重变化，单独或协同作用发生。2. 环境变化或直接抑制免疫系统功能，或通过引起免疫抑制神经内分泌反应间接影响免疫功能。3. 这种免疫功能的抑制，加上与季节相关的低温对异温免疫系统抵抗疾病能力的额外抑制作用，导致对嗜水气单胞菌等机会性病原体的易感性增加。反过来，易感性导致随后的疾病、个体死亡和种群消亡。工作假设的第二部分和第三部分将在项目期间在Bufo b. boreas, Rana yavapiensis， Bufo marinus和Ambystoma tigrinum中进行测试。我们的方法与其他致力于寻找两栖动物数量下降原因的方法的区别在于，其他人正在寻找足以直接杀死两栖动物的环境变化，而我们的方法评估的是足以导致免疫功能抑制和疾病的较小的、亚致命的变化的作用。

9400333 Carey Recent reports of world-wide declines and extinctions of amphibian populations have raised questions about the relation of environmental change to the demise of certain amphibian species. If these species are being harmed by man-made change, amphibians may prove to be excellent "harbingers of decay" and indicators of ecosystem stress. The causes of amphibian populational declines have not been conclusively demonstrated. %%% The following working hypothesis is presented to explain how environmental change might cause the demise of amphibian populations. 1. A sublethal change in one factor, or multiple change(s) in several factors, acting singly of synergistically, occurs in the environment of these amphibians. 2. The environmental change either directly suppresses function of immune system, or indirectly affects immune function by eliciting an immunosuppressive neuroendocrine response. 3. This depression of immune function, coupled with the additional suppressive effects of seasonally-associated cold body temperatures on the abilities of ectothermic immune systems to resist disease, leads to increased susceptibility to opportunistic pathogens such as Aeromonas hydrophila. In turn, susceptibility results in subsequent disease, death of the individual, and demise of the population. %%% Parts 2 and 3 of the working hypothesis will be tested in the project period in Bufo b. boreas, Rana yavapiensis, Bufo marinus, and Ambystoma tigrinum. The difference between our approach and that of others working to find the causes of amphibian declines is that others are looking to find an environmental change severe enough to kill amphibians directly, while our approach evaluates the role of smaller, sublethal changes sufficient to cause suppression of immune function and disease.