Low effective dispersal of asexual genotypes in heterogeneous landscapes by the endemic pathogen Penicillium marneffei.
Low effective dispersal of asexual genotypes in heterogeneous landscapes by the endemic pathogen Penicillium marneffei.
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DOI：
10.1371/journal.ppat.0010020
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发表时间：
2005-10
期刊：
影响因子：
6.7
通讯作者：
Vanittanakom, Nongnuch
中科院分区：
文献类型：
--
作者：
Fisher, Matthew C;Hanage, William P;de Hoog, Sybren;Johnson, Elizabeth;Smith, Michael D;White, Nicholas J;Vanittanakom, Nongnuch
微生物真核生物的长距离扩散已被证明导致在大陆和全球范围内建立种群。这种“无处不在的分散”被认为是微生物真核生物的一般特征，在大规模上使种群均匀化。然而，全球艾滋病大流行所造成的机会性传染病病原体的前所未有的采样表明，尽管通过空中散布的孢子进行长距离迁移，但一些重要的物种仍表现出地理上的地方性。一种机制，可能倾向于驱动这种地方性在面对空中传播是进化的小生境适应基因型时，有性生殖是罕见的。当自然生境异质时，这种无性生理“物种”的扩散将受到限制，这是适应性变异减少的结果。使用HIV相关的地方性真菌马尔尼菲青霉菌作为我们的模型，我们测量了两个宿主物种，人类和竹鼠在各种空间尺度上的遗传变异分布。我们的研究结果表明，尽管广泛的空中传播，分离的P.马尔尼菲在本地和全国范围内的寄主物种表现出广泛的空间遗传结构。我们表明，绝大多数的进化的P. marneffei基因组是克隆的，这可能是最无性的真菌尚未发现。我们表明，集群的基因型是特定的离散的生态区，并认为无性导致小生境适应基因型的进化，并推动地方性，通过减少这种病原体的潜力，在自然界中多样化。科学家们认为，微生物是通过气流传播到地球上的，这一假设被称为“无处不在的传播”。虽然真菌释放大量广泛分布的孢子，但不知道为什么许多物种仍然是地球仪周围特定地区的特有物种。作者的研究通过调查一种真菌的遗传结构，马尔尼菲青霉菌，提出了这个难题的答案，这种真菌会导致免疫系统受损的人患病。这项研究表明，马尔尼菲青霉孢子可以传播到很远的地方，但无法穿透它们所处的新环境。这似乎是因为真菌在很大程度上放弃了有性繁殖，这意味着它适应新挑战的能力有限。作者使用DNA分型表明，真菌的不同“克隆”与不同的环境有关，并表明对这些环境的适应限制了生物体在自然界中成功分散的能力。这可能解释了为什么马尔尼菲青霉只在东南亚一个相对较小的地区流行，作者继续提出，这种策略的长期后果可能是这种生物的最终灭绝。
Long-distance dispersal in microbial eukaryotes has been shown to result in the establishment of populations on continental and global scales. Such “ubiquitous dispersal” has been claimed to be a general feature of microbial eukaryotes, homogenising populations over large scales. However, the unprecedented sampling of opportunistic infectious pathogens created by the global AIDS pandemic has revealed that a number of important species exhibit geographic endemicity despite long-distance migration via aerially dispersed spores. One mechanism that might tend to drive such endemicity in the face of aerial dispersal is the evolution of niche-adapted genotypes when sexual reproduction is rare. Dispersal of such asexual physiological “species” will be restricted when natural habitats are heterogeneous, as a consequence of reduced adaptive variation. Using the HIV-associated endemic fungus Penicillium marneffei as our model, we measured the distribution of genetic variation over a variety of spatial scales in two host species, humans and bamboo rats. Our results show that, despite widespread aerial dispersal, isolates of P. marneffei show extensive spatial genetic structure in both host species at local and country-wide scales. We show that the evolution of the P. marneffei genome is overwhelmingly clonal, and that this is perhaps the most asexual fungus yet found. We show that clusters of genotypes are specific to discrete ecological zones and argue that asexuality has led to the evolution of niche-adapted genotypes, and is driving endemicity, by reducing this pathogen's potential to diversify in nature. Scientists believe that micro-organisms are spread around the planet on currents of air, a hypothesis that is known as “ubiquitous dispersal”. While fungi release huge quantities of widely dispersed spores, it is not known why many species remain endemic to specific regions around the globe. Research by the authors suggests an answer to this conundrum, by investigating the genetic structure of a fungus, Penicillium marneffei, that causes disease in people with damaged immune systems. This research has shown that P. marneffei spores can be dispersed over a wide distance, but fail to penetrate the new environments that they find themselves in. This appears to be because the fungus has largely dispensed with sexual reproduction, which means that its ability to adapt to new challenges is limited. The authors use DNA typing to show that different “clones” of the fungus are associated with different environments, and suggest that adaptation to these environments is constraining the organism's ability to successfully disperse in nature. This may explain why P. marneffei is endemic to a relatively small area of southeast Asia, and the authors go on to suggest that the long-term consequence of this strategy may be the eventual extinction of the organism.