Cryptic infection of a broad taxonomic and geographic diversity of tadpoles by Perkinsea protists
Cryptic infection of a broad taxonomic and geographic diversity of tadpoles by Perkinsea protists
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DOI：
10.1073/pnas.1500163112
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发表时间：
2015-08-25
影响因子：
11.1
通讯作者：
Richards, Thomas A.
中科院分区：
文献类型：
--
作者：
Chambouvet, Aurelie;Gower, David J.;Richards, Thomas A.
两栖动物种群的减少，特别是青蛙，经常被引用作为支持地球正在经历第六次大规模灭绝事件的一个例子。两栖动物似乎对新出现的疾病特别敏感（例如，真菌和病毒病原体），但感染性病原体的多样性和地理分布才刚刚开始调查。最近的工作将一种以前未描述的原生生物与美国的大规模死亡事件联系起来，在这种事件中，受感染的青蛙蝌蚪有一个异常增大的黄色肝脏，里面充满了一种假定的寄生虫的原生生物细胞。系统发育分析显示，这种传染性病原体隶属于Perkinsea：一种寄生在肺泡内的寄生群，以Perkinsus sp.为例，一种“海洋”原生生物，负责商业贝类种群的大规模死亡事件。使用小亚基（SSU）核糖体DNA（rDNA）测序，我们开发了一个有针对性的PCR协议，优先采样的珀金斯的一个分支。我们在淡水环境DNA上测试了该协议，揭示了这些环境中Perkinsea谱系的广泛多样性。然后，我们使用相同的协议来测试来自多个青蛙家族的182只蝌蚪的肝脏中的Perkinsea样谱系。我们确定了一个独特的Perkinsea分支，包括低水平的SSU rDNA变异不同的血统以前与蝌蚪大规模死亡事件。这个分支的成员存在于38个蝌蚪样品从14个不同的属/类群，来自五个国家横跨三大洲。据我们所知，这些数据提供了第一个证据表明，在热带和温带环境中，包括海洋岛屿，Perkinsea类原生生物感染了广泛的青蛙分类范围内的蝌蚪。
The decline of amphibian populations, particularly frogs, is often cited as an example in support of the claim that Earth is undergoing its sixth mass extinction event. Amphibians seem to be particularly sensitive to emerging diseases (e.g., fungal and viral pathogens), yet the diversity and geographic distribution of infectious agents are only starting to be investigated. Recent work has linked a previously undescribed protist with mass-mortality events in the United States, in which infected frog tadpoles have an abnormally enlarged yellowish liver filled with protist cells of a presumed parasite. Phylogenetic analyses revealed that this infectious agent was affiliated with the Perkinsea: a parasitic group within the alveolates exemplified by Perkinsus sp., a "marine" protist responsible for mass-mortality events in commercial shellfish populations. Using small subunit (SSU) ribosomal DNA (rDNA) sequencing, we developed a targeted PCR protocol for preferentially sampling a clade of the Perkinsea. We tested this protocol on freshwater environmental DNA, revealing a wide diversity of Perkinsea lineages in these environments. Then, we used the same protocol to test for Perkinsea-like lineages in livers of 182 tadpoles from multiple families of frogs. We identified a distinct Perkinsea clade, encompassing a low level of SSU rDNA variation different from the lineage previously associated with tadpole mass-mortality events. Members of this clade were present in 38 tadpoles sampled from 14 distinct genera/phylogroups, from five countries across three continents. These data provide, to our knowledge, the first evidence that Perkinsea-like protists infect tadpoles across a wide taxonomic range of frogs in tropical and temperate environments, including oceanic islands.