Emerging infectious diseases (EIDs) are contributing to species die-offs worldwide. We can better understand EIDs by using ecological approaches to study pathogen biology. For example, pathogens are exposed to variable temperatures across daily, seasonal, and annual scales. Exposure to temperature fluctuations may reduce pathogen growth and reproduction, which could affect pathogen virulence, transmission, and environmental persistence with implications for disease. We examined the effect of a variable thermal environment on reproductive life history traits of the fungal pathogen Batrachochytrium dendrobatidis (Bd). Bd causes chytridiomycosis, an emerging infectious disease of amphibians. As a pathogen of ectothermic hosts, Bd can be exposed to large temperature fluctuations in nature. To determine the effect of fluctuating temperatures on Bd growth and reproduction, we collected temperature data from breeding pools of the Yosemite toad (Anaxyrus canorus), a federally threatened species that is susceptible to chytridiomycosis. We cultured Bd under a daily fluctuating temperature regime that simulated Yosemite toad breeding pool temperatures and measured Bd growth, reproduction, fecundity, and viability. We observed decreased Bd growth and reproduction in a diurnally fluctuating thermal environment as compared to cultures grown at constant temperatures within the optimal Bd thermal range. We also found that Bd exhibits temperature-induced trade-offs under constant low and constant high temperature conditions. Our results provide novel insights on variable responses of Bd to dynamic thermal conditions and highlight the importance of incorporating realistic temperature fluctuations into investigations of pathogen ecology and EIDs.

中文翻译：

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每日波动的温度会降低培养物中致命的两栖真菌病原体的生长和繁殖速率。

新兴传染病（EID）助长了全球物种灭绝。通过使用生态学方法研究病原体生物学，我们可以更好地了解EID。例如，病原体在每日，季节性和年度范围内都暴露于变化的温度下。暴露于温度波动下可能会减少病原体的生长和繁殖，这可能会影响病原体的毒力，传播和环境持久性，进而影响疾病。我们检查了变化的热环境对真菌病原体Batrachochytrium dendrobatidis（Bd）的生殖生活史特征的影响。Bd引起壶菌病，一种两栖动物的新兴传染病。作为外吸宿主的病原体，Bd可能会暴露于自然界中较大的温度波动中。为了确定温度波动对Bd生长和繁殖的影响，我们从优胜美地蟾蜍（Anaxyrus canorus）的繁殖池中收集了温度数据，优胜美地蟾蜍是受乳糜菌滋养的受到联邦威胁的物种。我们在模拟优胜美地蟾蜍繁殖池温度的每日波动温度范围内培养了Bd，并测量了Bd的生长，繁殖，繁殖力和生存能力。我们观察到，与在最佳Bd热范围内恒定温度下培养的培养物相比，Bd在昼夜波动的热环境中的生长和繁殖减少。我们还发现，在恒定的低温和恒定的高温条件下，Bd表现出温度引起的折衷。