Cophylogeny of the anther smut fungi and their caryophyllaceous hosts
Cophylogeny of the anther smut fungi and their caryophyllaceous hosts
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花药黑粉病真菌及其石竹宿主的系统发育
DOI：
10.3929/ethz-a-005751731
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发表时间：
2008
影响因子：
3.4
通讯作者：
T. Giraud
中科院分区：
文献类型：
--
作者：
Guislaine Refrégier;M. L. Gac;Florian Jabbour;A. Widmer;J. Shykoff;R. Yockteng;M. Hood;T. Giraud
背景：使用系统发育方法，寄生虫和宿主之间应该发生平行分支发生的预期已在一些研究中得到验证，但大多数其他研究提供了宿主频繁转移的证据。在这里，我们研究了引起花药黑粉病的小葡萄属真菌与其石竹宿主之间关联的进化历史。我们研究了宿主和寄生虫系统发育之间的一致性，推断了共种事件和宿主转移，并评估了地理或植物生态学是否可以促进所确定的假定宿主转移。对于微生物的共系统发育分析，从不同宿主物种中分离出的寄生虫菌株通常被认为代表独立的进化谱系，通常不检查某些菌株是否实际上属于同一通才物种。如果在密切相关的宿主上发现通才物种，这种方法可能会将种内节点误认为是物种形成事件，从而使共系统发育分析的结果产生偏差。因此，本研究的第二个目的是评估物种界定对共种推论的影响。结果：我们推断了来自多个地理来源的 21 种寄主植物的花药黑粉病菌株的多基因系统发育，补充了之前关于真菌物种及其寄主特异性的界定研究。我们还推断了其寄主植物的多基因系统发育，并对两种系统发育进行了比较。当每个宿主物种被认为含有特定的寄生虫菌株时，即当不认识到通用寄生虫物种时，就会发现显着水平的共物种。这种方法高估了 cocladogenesis 的频率，因为在密切相关的宿主上发现了能够感染多个宿主物种（即通才）的单个寄生虫物种。当适当地界定通才寄生虫物种并且仅保留每个物种的一个代表时，共种事件不会比随机分布下预期的更频繁，并且可以推断出许多宿主转移。目前宿主物种的地理分布似乎与理解假定的历史宿主转变无关，因为大多数真菌物种具有重叠的地理范围。我们确实发现了一些被密切相关的花药黑粉病物种患病的寄主物种之间的一些生态相似性，包括共享的传粉媒介和栖息地类型。总体而言，宿主-寄生虫相互作用背后的遗传相似性似乎对特化和宿主转移具有最重要的影响：在密切相关的植物物种上发现了通才多宿主寄生虫物种，并且Microbotryum系统发育中的相关物种与同一宿主进化枝的成员相关。结论：我们在此表明，Microbotryum 物种是通过频繁的宿主转移到中等距离的宿主而进化的，并且我们进一步表明，准确界定寄生虫物种对于解释共系统发育研究至关重要。
Background: Using phylogenetic approaches, the expectation that parallel cladogenesis should occur between parasites and hosts has been validated in some studies, but most others provided evidence for frequent host shifts. Here we examine the evolutionary history of the association between Microbotryum fungi that cause anther smut disease and their Caryophyllaceous hosts. We investigated the congruence between host and parasite phylogenies, inferred cospeciation events and host shifts, and assessed whether geography or plant ecology could have facilitated the putative host shifts identified. For cophylogeny analyses on microorganisms, parasite strains isolated from different host species are generally considered to represent independent evolutionary lineages, often without checking whether some strains actually belong to the same generalist species. Such an approach may mistake intraspecific nodes for speciation events and thus bias the results of cophylogeny analyses if generalist species are found on closely related hosts. A second aim of this study was therefore to evaluate the impact of species delimitation on the inferences of cospeciation. Results: We inferred a multiple gene phylogeny of anther smut strains from 21 host plants from several geographic origins, complementing a previous study on the delimitation of fungal species and their host specificities. We also inferred a multi-gene phylogeny of their host plants, and the two phylogenies were compared. A significant level of cospeciation was found when each host species was considered to harbour a specific parasite strain, i.e. when generalist parasite species were not recognized as such. This approach overestimated the frequency of cocladogenesis because individual parasite species capable of infecting multiple host species (i.e. generalists) were found on closely related hosts. When generalist parasite species were appropriately delimited and only a single representative of each species was retained, cospeciation events were not more frequent than expected under a random distribution, and many host shifts were inferred. Current geographic distributions of host species seemed to be of little relevance for understanding the putative historical host shifts, because most fungal species had overlapping geographic ranges. We did detect some ecological similarities, including shared pollinators and habitat types, between host species that were diseased by closely related anther smut species. Overall, genetic similarity underlying the host-parasite interactions appeared to have the most important influence on specialization and host-shifts: generalist multi-host parasite species were found on closely related plant species, and related species in the Microbotryum phylogeny were associated with members of the same host clade. Conclusion: We showed here that Microbotryum species have evolved through frequent host shifts to moderately distant hosts, and we show further that accurate delimitation of parasite species is essential for interpreting cophylogeny studies.