Data from: Realistic heat pulses protect frogs from disease under simulated rainforest frog thermal regimes

Recent emergences of fungal diseases have caused catastrophic global losses of biodiversity. Temperature is one of the most important factors influencing host-fungus associations but the effects of temperature variability on disease development are rarely examined. The chytrid pathogen Batrachochytrium dendrobatidis (Bd) has had severe effects on populations of hundreds of rainforest-endemic amphibian species but we know little about the effects of rainforest-specific host body temperature cycles on infection patterns. To address this challenge, we used body temperature regimes experienced in nature by frogs in the Australian Wet Tropics to guide a controlled experiment investigating the effects of body temperature fluctuations on infection patterns in a model host (Litoria spenceri), with emphasis on exposing frogs to realistic ‘heat pulses’ that only marginally exceed the thermal optimum of the fungus. We then exposed cultured Bd to an expanded array of heat pulse treatments and measured parameters of population growth to help resolve the role of host immunity in our in vivo results. Infections developed more slowly in frogs exposed to daily 4-h heat pulses of 26°C or 29°C than in frogs in constant temperature treatments without heat pulses (control). Frogs that experienced heat pulses were also less likely to exceed infection intensities at which morbidity and mortality become likely. Ten of 11 (91%) frogs from the daily 29°C heat pulse treatment even cleared their infections after approximately nine weeks. Cultured Bd also grew more slowly when exposed to heat pulses than in constant-temperature control treatments, suggesting that mild heat pulses have direct negative effects on Bd growth in nature, but precluding us from determining whether there was a concurrent benefit of heat pulses to host immunity. Our results suggest that even in habitats where average temperatures may be suitable for fungal growth and reproduction, infection risk or the outcome of existing infections may be heavily influenced by short but frequent exposures to temperatures that only slightly exceed the optimum for the fungus. Our findings provide support for management interventions that promote warm microenvironments for hosts, such as small-scale removal of branches overhanging critical habitat or provision of artificial heat sources.

近年来，真菌病害的暴发已造成全球生物多样性的灾难性损失。温度是影响宿主-真菌互作关系的关键因子之一，但温度波动对病害发生发展的影响却鲜有研究。壶菌病原菌蛙壶菌（Batrachochytrium dendrobatidis, Bd）已对数百种雨林特有两栖动物种群造成严重破坏，但我们对雨林特有的宿主体温节律如何影响感染模式仍知之甚少。为解决这一科学难题，我们以澳大利亚湿热带地区蛙类在自然环境中经历的体温节律为参照，开展以斯潘塞氏雨滨蛙（Litoria spenceri）为模式宿主的受控实验，探究体温波动对感染模式的影响，重点设置了仅略微超出该真菌热最适温度的真实模拟‘热脉冲’暴露处理。随后，我们将体外培养的蛙壶菌置于更广泛的热脉冲处理梯度下，测定其种群生长相关参数，以辅助解析宿主免疫在体内实验结果中的作用机制。与无热脉冲的恒温对照组相比，每日接受4小时26℃或29℃热脉冲处理的蛙类，其感染进程显著更为缓慢；接受热脉冲处理的蛙类，其感染强度达到致病与致死阈值的概率也显著降低。在每日29℃热脉冲处理组的11只蛙类中，更有10只（占比91%）在约9周后成功清除了体内感染。体外培养的蛙壶菌在热脉冲处理下的生长速度同样慢于恒温对照组，这表明轻度热脉冲可对自然环境中蛙壶菌的生长产生直接抑制作用，但我们无法确定热脉冲是否同时为宿主免疫带来了额外增益。本研究结果显示，即便在平均温度适宜真菌生长繁殖的生境中，感染风险或现有感染的转归，也可能受到短期但频繁暴露于仅略高于该真菌热最适温度环境的显著影响。本研究结果可为宿主相关的温度调控干预措施提供理论支撑，例如通过小规模移除关键生境上方的悬垂枝条，或设置人工热源，为宿主营造温暖微生境。