Data from: Skin sloughing rate increases with chytrid fungus infection load in a susceptible amphibian

1. Amphibian chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), is responsible for the greatest disease-driven loss of vertebrate biodiversity in recorded history. Understanding drivers of host susceptibility to this cutaneous disease is hindered by gaps in our knowledge of the host–pathogen relationship. One such overlooked aspect of susceptibility is variation in skin maintenance processes, particularly skin turnover via routine sloughing. It has been suggested that sloughing plays a role in immune defence, by removing skin-associated microbes. Thus, skin sloughing may play an important role in the pathogenesis of chytridiomycosis. 2. To determine the relationship between skin sloughing and disease progression, we exposed adult Australian green tree frogs (Litoria caerulea) to a local Bd strain and monitored sloughing rates and individual infection loads on a naturalistic cycling temperature regime (15–23 °C). 3. We determined sloughing rates in real-time by using an array of infrared video cameras to film frog behaviour and monitored infection load before and after sloughing by swabbing and analysis with quantitative PCR. 4. We found that sloughing rate increased with Bd infection load in infected frogs, but sloughing itself did not affect Bd load on the ventral skin surface. Furthermore, Bd infection did not affect the duration of characteristic sloughing behaviour, and sloughing retained rhythmicity even at high infection loads. 5. Although an increased sloughing rate might be considered advantageous for Bd-infected animals, it does not appear to curb the progression of disease and may actually contribute to the loss of physiological homoeostasis seen in terminally ill frogs by further inhibiting water and electrolyte transport across the skin. 6. By measuring sloughing rates directly for the first time, our results shed light on how Bd interacts with the physiological processes of the skin and indicate that variation in skin sloughing frequency may play a role in the observed inter- and intraspecific variation in susceptibility to disease.

1. 由真菌病原体蛙壶菌（Batrachochytrium dendrobatidis，简称Bd）引发的两栖动物壶菌病，是有记录以来由疾病驱动的脊椎动物生物多样性丧失最严重的事件。当前，我们对宿主-病原体互作（host–pathogen relationship）的认知存在空白，这阻碍了我们对该皮肤类疾病宿主易感性驱动因素的解析。其中一个被长期忽视的易感性维度，便是皮肤维护过程的差异，尤其是通过常规蜕皮实现的皮肤更新（skin turnover）。已有研究表明，蜕皮可通过清除皮肤定植的微生物，在免疫防御中发挥作用。因此，皮肤蜕皮可能在壶菌病的发病机制中占据重要地位。
2. 为明确皮肤蜕皮与疾病进展之间的关联，我们将成年澳大利亚绿树蛙（Litoria caerulea）暴露于本地Bd菌株中，并在自然温度循环环境（15–23℃）下监测其蜕皮速率与个体感染载荷。
3. 我们通过多组红外视频摄像机（infrared video cameras）录制蛙类行为以实时测定蜕皮速率；同时在蜕皮前后通过棉拭子采样结合定量PCR（quantitative PCR）分析，监测感染载荷的变化。
4. 研究结果显示，感染Bd的青蛙其蜕皮速率随感染载荷升高而增加，但蜕皮本身并未对腹侧皮肤表面的Bd载荷产生影响。此外，Bd感染并未改变典型蜕皮行为的持续时长，即便在高感染载荷下，蜕皮仍可保持固有节律性。
5. 尽管蜕皮速率提升对Bd感染个体而言或许被视为有利，但这似乎并未抑制疾病进展，反而可能通过进一步抑制皮肤的水和电解质转运过程，加剧终末期病蛙所出现的生理稳态（physiological homoeostasis）失衡。
6. 本研究首次实现了蜕皮速率的直接测定，研究结果阐明了Bd与皮肤生理过程的相互作用模式，并表明皮肤蜕皮频率的差异，可能是造成不同物种间以及同一物种内疾病易感性差异的关键因素之一。