Department of Biology, San Francisco State University, San Francisco, California, United States of America.
PLoS One. 2012;7(3):e33567. doi: 10.1371/journal.pone.0033567. Epub 2012 Mar 12.
Chytridiomycosis, a disease caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), is driving amphibian declines and extinctions in protected areas globally. The introduction of invasive reservoir species has been implicated in the spread of Bd but does not explain the appearance of the pathogen in remote protected areas. In the high elevation (>1500 m) Sierra Nevada of California, the native Pacific chorus frog, Pseudacris regilla, appears unaffected by chytridiomycosis while sympatric species experience catastrophic declines. We investigated whether P. regilla is a reservoir of Bd by comparing habitat occupancy before and after a major Bd outbreak and measuring infection in P. regilla in the field, monitoring susceptibility of P. regilla to Bd in the laboratory, examining tissues with histology to determine patterns of infection, and using an innovative soak technique to determine individual output of Bd zoospores in water. Pseudacris regilla persists at 100% of sites where a sympatric species has been extirpated from 72% in synchrony with a wave of Bd. In the laboratory, P. regilla carried loads of Bd as much as an order of magnitude higher than loads found lethal to sympatric species. Histology shows heavy Bd infection in patchy areas next to normal skin, a possible mechanism for tolerance. The soak technique was 77.8% effective at detecting Bd in water and showed an average output of 68 zoospores per minute per individual. The results of this study suggest P. regilla should act as a Bd reservoir and provide evidence of a tolerance mechanism in a reservoir species.
蛙壶菌病是一种由真菌病原体蛙壶菌（Batrachochytrium dendrobatidis，Bd）引起的疾病，正在导致全球保护区内的两栖动物数量减少和灭绝。入侵的储存物种的引入被认为是 Bd 传播的原因，但不能解释病原体在偏远保护区出现的原因。在加利福尼亚高海拔 (>1500 米) 的内华达山脉，本地的太平洋角蟾， Pseudacris regilla，似乎没有受到蛙壶菌病的影响，而共生的物种则经历了灾难性的减少。我们通过比较 Bd 大规模爆发前后的栖息地占有率、测量野外 P. regilla 的感染情况、在实验室监测 P. regilla 对 Bd 的敏感性、用组织学检查确定感染模式以及使用创新的浸泡技术来确定 Bd 游动孢子在水中的个体产量，来研究 P. regilla 是否是 Bd 的储存宿主。P. regilla 在与 Bd 波同步灭绝的 72%的共生物种所在的 100%的地点中仍然存在。在实验室中，P. regilla 携带的 Bd 负荷比共生物种致命负荷高一个数量级。组织学显示，在正常皮肤旁边的斑块区域有大量的 Bd 感染，这可能是一种耐受机制。浸泡技术在水中检测 Bd 的有效率为 77.8%，平均每分钟每个个体产生 68 个游动孢子。这项研究的结果表明，P. regilla 应该充当 Bd 的储存宿主，并为储存物种中的耐受机制提供证据。
