Rapid global expansion of the fungal disease chytridiomycosis into declining and healthy amphibian populations.
Rapid global expansion of the fungal disease chytridiomycosis into declining and healthy amphibian populations.
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DOI：
10.1371/journal.ppat.1000458
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发表时间：
2009-05
期刊：
影响因子：
6.7
通讯作者：
Longcore JE
中科院分区：
文献类型：
--
作者：
James TY;Litvintseva AP;Vilgalys R;Morgan JA;Taylor JW;Fisher MC;Berger L;Weldon C;du Preez L;Longcore JE
由壶菌引起的真菌疾病壶菌病是一个谜，因为它在全球范围内既发生在下降的两栖动物种群中，也发生在明显健康的（非下降的）两栖动物种群中。这种分布引发了关于在最近发现的地点，病原体是被引入的还是地方性的争论。在这项研究中，我们利用来自17个核位点的DNA序列变异和线粒体基因组的大片段，对全球收集的真菌菌株进行了分子群体遗传学研究，这些真菌菌株来自衰退和健康两栖动物种群。我们发现DNA多态性率较低，每个位点仅检测到两个序列等位基因，但二倍体基因型具有很高的多样性。一半的位点显示出过量的杂合基因型，与主要的克隆繁殖模式一致。尽管没有明显的性别差异，但基因型多样性较高（59个菌株中有44个独特的基因型）。我们提供的证据表明，观察到的基因型变异可以通过有丝分裂重组产生杂合性的损失。从牛蛙中分离出的一种菌株具有与全球样本相同的等位基因多样性，这表明当前的流行病可以追溯到单克隆谱系的爆发。这些数据与目前壶菌病的流行是一致的，这是由一种新的病原体引起的，最近范围迅速扩大。同一谱系在健康人群和数量下降人群中的广泛出现表明，该病的结果取决于环境因素和宿主的抵抗力。两栖动物物种正面临着前所未有的全球性灭绝危机。导致其数量下降的主要因素是新出现的壶菌病和栖息地的破坏。壶菌病是由水生真菌壶菌（Batrachochytrium dendroatidis）引起的，与澳大利亚、巴拿马、北美和西班牙等山区的物种灭绝和人口下降有关。目前，关于最近病原体的出现是否主要是由环境因素引发地方性病原体暴发的结果，还是由于病原体被广泛引入naïve宿主种群（“病原体污染”）而引起的流行病，存在争议。我们研究了壶菌病的群体遗传学使用DNA序列从全球面板的菌株。这些数据表明，在该病原体的历史中存在一个强大的遗传瓶颈，而且该流行病似乎可追溯到单一基因型的广泛传播。种群不按宿主来源构成，在抗性和高度敏感的物种种群中均检测到相同的谱系。这些数据表明壶菌病的流行是由一种新的病原体的出现引起的，但疾病的结果取决于宿主的耐药性和环境因素。
The fungal disease chytridiomycosis, caused by Batrachochytrium dendrobatidis, is enigmatic because it occurs globally in both declining and apparently healthy (non-declining) amphibian populations. This distribution has fueled debate concerning whether, in sites where it has recently been found, the pathogen was introduced or is endemic. In this study, we addressed the molecular population genetics of a global collection of fungal strains from both declining and healthy amphibian populations using DNA sequence variation from 17 nuclear loci and a large fragment from the mitochondrial genome. We found a low rate of DNA polymorphism, with only two sequence alleles detected at each locus, but a high diversity of diploid genotypes. Half of the loci displayed an excess of heterozygous genotypes, consistent with a primarily clonal mode of reproduction. Despite the absence of obvious sex, genotypic diversity was high (44 unique genotypes out of 59 strains). We provide evidence that the observed genotypic variation can be generated by loss of heterozygosity through mitotic recombination. One strain isolated from a bullfrog possessed as much allelic diversity as the entire global sample, suggesting the current epidemic can be traced back to the outbreak of a single clonal lineage. These data are consistent with the current chytridiomycosis epidemic resulting from a novel pathogen undergoing a rapid and recent range expansion. The widespread occurrence of the same lineage in both healthy and declining populations suggests that the outcome of the disease is contingent on environmental factors and host resistance. Amphibian species are facing a current global extinction crisis of unprecedented magnitude. The major factors causing their decline are the emerging disease chytridiomycosis and habitat destruction. Chytridiomycosis is caused by the aquatic fungus Batrachochytrium dendrobatidis and has been linked to species extinctions and population declines in montane regions including Australia, Panama, North America, and Spain. Currently, it is debated whether the recent emergence of the pathogen is largely the result of environmental factors triggering an outbreak of an endemic pathogen or if the epidemic has been caused by widespread introduction of the pathogen into naïve host populations (“pathogen pollution”). We studied the population genetics of chytridiomycosis using DNA sequences from a global panel of strains. These data showed evidence of a strong genetic bottleneck in the history of the pathogen, and the epidemic appears traceable to the widespread dispersal of a single genotype. Populations were not structured by host-origin, and the same lineage was detected in populations of both resistant and highly sensitive species. The data suggest that the chytridiomycosis epidemic is caused by the emergence of a novel pathogen but that disease outcome is contingent on host resistance and environmental factors.
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