Evolutionary changes in symbiont community structure in ticks
Evolutionary changes in symbiont community structure in ticks
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DOI：
10.1111/mec.14094
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发表时间：
2017-06-01
影响因子：
4.9
通讯作者：
Chevillon, Christine
中科院分区：
文献类型：
--
作者：
Duron, Olivier;Binetruy, Florian;Chevillon, Christine
对受限饮食生态位的生态专业化是由许多节肢动物谱系中的专性且通常是母系遗传的共生体驱动的。这些可遗传的共生体通常与节肢动物形成进化上稳定的联系，可以持续数百万年。最近发现蜱虫体内含有一种专性共生体 Coxiella-LE，它可以合成从血液饮食中无法获得足够数量的 B 族维生素和辅因子。在这项研究中，对 81 种蜱虫的检查表明，一些柯克斯体-LE 共生体在进化上是稳定的，先是在古老的习得过程中观察到，然后是在属于扇头蜱属的蜱虫中观察到的共同多样化。然而，许多其他 Coxiella-LE 共生体的特点是进化稳定性低，宿主转移和灭绝事件频繁。进一步的检查发现蜱虫中还存在其他九个母系遗传细菌。尽管这九种共生体最初被认为是兼性的，但它们在蜱种中的分布表明，至少四种可能独立取代了 Coxiella-LE，并且可能代表替代的专性共生体。系统发育证据表明，在这些共生体中，cocladogenesis 在全球范围内都很罕见，因为大多数都是通过现有共生体在不相关的蜱种之间的水平转移而产生的。因此，这些共生群落的结构在蜱的系统发育过程中并不是固定和稳定的。最重要的是，共生群落通常达到高水平的多样性，宿主物种内共存有多达六种不相关的母系遗传细菌。我们进一步推测，共存共生体之间的相互作用是蜱种之间和内部群落结构的关键驱动因素。
Ecological specialization to restricted diet niches is driven by obligate, and often maternally inherited, symbionts in many arthropod lineages. These heritable symbionts typically form evolutionarily stable associations with arthropods that can last for millions of years. Ticks were recently found to harbour such an obligate symbiont, Coxiella-LE, that synthesizes B vitamins and cofactors not obtained in sufficient quantities from blood diet. In this study, the examination of 81 tick species shows that some Coxiella-LE symbioses are evolutionarily stable with an ancient acquisition followed by codiversification as observed in ticks belonging to the Rhipicephalus genus. However, many other Coxiella-LE symbioses are characterized by low evolutionary stability with frequent host shifts and extinction events. Further examination revealed the presence of nine other genera of maternally inherited bacteria in ticks. Although these nine symbionts were primarily thought to be facultative, their distribution among tick species rather suggests that at least four may have independently replaced Coxiella-LE and likely represent alternative obligate symbionts. Phylogenetic evidence otherwise indicates that cocladogenesis is globally rare in these symbioses as most originate via horizontal transfer of an existing symbiont between unrelated tick species. As a result, the structure of these symbiont communities is not fixed and stable across the tick phylogeny. Most importantly, the symbiont communities commonly reach high levels of diversity with up to six unrelated maternally inherited bacteria coexisting within host species. We further conjecture that interactions among coexisting symbionts are pivotal drivers of community structure both among and within tick species.