Murphy Peter J, St-Hilaire Sophie, Corn Paul Stephen
Department of Biological Sciences, Idaho State University, 650 Memorial Dr., Pocatello, Idaho 83209-8007, USA.
Dis Aquat Organ. 2011 May 24;95(1):31-42. doi: 10.3354/dao02336.
Prevalence of the pathogen Batrachochytrium dendrobatidis (Bd), implicated in amphibian population declines worldwide, is associated with habitat moisture and temperature, but few studies have varied these factors and measured the response to infection in amphibian hosts. We evaluated how varying humidity, contact with water, and temperature affected the manifestation of chytridiomycosis in boreal toads Anaxyrus (Bufo) boreas boreas and how prior exposure to Bd affects the likelihood of survival after re-exposure, such as may occur seasonally in long-lived species. Humidity did not affect survival or the degree of Bd infection, but a longer time in contact with water increased the likelihood of mortality. After exposure to approximately 10(6) Bd zoospores, all toads in continuous contact with water died within 30 d. Moreover, Bd-exposed toads that were disease-free after 64 d under dry conditions, developed lethal chytridiomycosis within 70 d of transfer to wet conditions. Toads in unheated aquaria (mean = 15 degrees C) survived less than 48 d, while those in moderately heated aquaria (mean = 18 degrees C) survived 115 d post-exposure and exhibited behavioral fever, selecting warmer sites across a temperature gradient. We also found benefits of prior Bd infection: previously exposed toads survived 3 times longer than Bd-naïve toads after re-exposure to 106 zoospores (89 vs. 30 d), but only when dry microenvironments were available. This study illustrates how the outcome of Bd infection in boreal toads is environmentally dependent: when continuously wet, high reinfection rates may overwhelm defenses, but periodic drying, moderate warming, and previous infection may allow infected toads to extend their survival.
全球两栖动物数量减少与致病真菌蛙壶菌（Batrachochytrium dendrobatidis，简称Bd）的流行有关，该真菌与栖息地湿度和温度相关，但很少有研究改变这些因素并测量两栖动物宿主对感染的反应。我们评估了湿度变化、与水的接触以及温度如何影响北方蟾蜍（Anaxyrus (Bufo) boreas boreas）的壶菌病表现，以及先前暴露于Bd如何影响再次暴露后的存活可能性，比如在长寿物种中可能季节性发生的情况。湿度并不影响存活率或Bd感染程度，但与水接触的时间延长会增加死亡可能性。暴露于约10⁶个Bd游动孢子后，所有持续与水接触的蟾蜍在30天内死亡。此外，在干燥条件下64天后未患病的暴露于Bd的蟾蜍，转移到潮湿条件下70天内会患上致命的壶菌病。未加热水族箱（平均温度 = 15摄氏度）中的蟾蜍存活不到48天，而适度加热水族箱（平均温度 = 18摄氏度）中的蟾蜍在暴露后存活了115天，并表现出行为性发热，在温度梯度中选择较温暖的地点。我们还发现先前感染Bd有好处：再次暴露于10⁶个游动孢子后，先前暴露的蟾蜍存活时间比未接触过Bd的蟾蜍长3倍（89天对30天），但前提是有干燥的微环境。这项研究说明了北方蟾蜍中Bd感染的结果如何依赖于环境：当持续潮湿时，高再感染率可能会压倒防御能力，但周期性干燥、适度升温以及先前感染可能会使受感染的蟾蜍延长存活时间。
