Department of Biology, San Francisco State University, San Francisco, California, United States of America.
Museum of Vertebrate Zoology, University of California Berkeley, Berkeley, California, United States of America.
PLoS One. 2019 Sep 19;14(9):e0219981. doi: 10.1371/journal.pone.0219981. eCollection 2019.
Amphibians, the most threatened group of vertebrates, are seen as indicators of the sixth mass extinction on earth. Thousands of species are threatened with extinction and many have been affected by an emerging infectious disease, chytridiomycosis, caused by the fungal pathogen, Batrachochytrium dendrobatidis (Bd). However, amphibians exhibit different responses to the pathogen, such as survival and population persistence with infection, or mortality of individuals and complete population collapse after pathogen invasion. Multiple factors can affect host pathogen dynamics, yet few studies have provided a temporal view that encompasses both the epizootic phase (i.e. pathogen invasion and host collapse), and the transition to a more stable co-existence (i.e. recovery of infected host populations). In the Sierra Nevada mountains of California, USA, conspecific populations of frogs currently exhibit dramatically different host/ Bd-pathogen dynamics. To provide a temporal context by which present day dynamics may be better understood, we use a Bd qPCR assay to test 1165 amphibian specimens collected between 1900 and 2005. Our historical analyses reveal a pattern of pathogen invasion and eventual spread across the Sierra Nevada over the last century. Although we found a small number of Bd-infections prior to 1970, these showed no sign of spread or increase in infection prevalence over multiple decades. After the late 1970s, when mass die offs were first noted, our data show Bd as much more prevalent and more spatially spread out, suggesting epizootic spread. However, across the ~400km2 area, we found no evidence of a wave-like pattern, but instead discovered multiple, nearly-simultaneous invasions within regions. We found that Bd invaded and spread in the central Sierra Nevada (Yosemite National Park area) about four decades before it invaded and spread in the southern Sierra Nevada (Sequoia and Kings Canyon National Parks area), and suggest that the temporal pattern of pathogen invasion may help explain divergent contemporary host pathogen dynamics.
两栖动物是脊椎动物中受威胁最严重的群体，被视为地球上第六次大灭绝的指标。数千个物种面临灭绝的威胁，许多物种受到一种新兴传染病——蛙壶菌病（chytridiomycosis）的影响，这种病是由真菌病原体 Batrachochytrium dendrobatidis（Bd）引起的。然而，两栖动物对病原体的反应不同，例如在感染后存活和种群持续存在，或者个体死亡和病原体入侵后整个种群崩溃。多种因素会影响宿主病原体动态，但很少有研究提供了一个时间视角，包括流行病阶段（即病原体入侵和宿主崩溃）以及向更稳定共存的转变（即受感染宿主种群的恢复）。在美国加利福尼亚州内华达山脉，同种青蛙种群目前表现出截然不同的宿主/Bd-病原体动态。为了提供一个时间背景，以便更好地理解当前的动态，我们使用 Bd qPCR 检测方法测试了 1900 年至 2005 年间采集的 1165 个两栖动物标本。我们的历史分析揭示了过去一个世纪内病原体入侵并最终在整个内华达山脉传播的模式。尽管我们在 1970 年之前发现了少量的 Bd 感染，但这些感染没有显示出在几十年内传播或感染率增加的迹象。自 20 世纪 70 年代末首次注意到大规模死亡以来，我们的数据表明 Bd 更为普遍，分布范围更广，表明出现了流行病传播。然而，在大约 400 平方公里的区域内，我们没有发现类似波浪的模式，而是发现了多个几乎同时发生的入侵区域。我们发现，Bd 在内华达山脉中部（约塞米蒂国家公园地区）的入侵和传播大约比在南部（红杉和国王峡谷国家公园地区）早了四十年，并且病原体入侵的时间模式可能有助于解释当前宿主病原体动态的差异。
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