Zhukova Mariya, Sapountzis Panagiotis, Schiøtt Morten, Boomsma Jacobus J
Centre for Social Evolution, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
Front Microbiol. 2017 Oct 10;8:1942. doi: 10.3389/fmicb.2017.01942. eCollection 2017.
The social Hymenoptera have distinct larval and adult stages separated by metamorphosis, which implies striking remodeling of external and internal body structures during the pupal stage. This imposes challenges to gut symbionts as existing cultures are lost and may or may not need to be replaced. To elucidate the extent to which metamorphosis interrupts associations between bacteria and hosts, we analyzed changes in gut microbiota during development and traced the transmission routes of dominant symbionts from the egg to adult stage in the leaf-cutting ants and , which are both important functional herbivores in the New World tropics. Bacterial density remained similar across the developmental stages of , but brood had very low bacterial prevalences suggesting that bacterial gut symbionts are not actively maintained. We found that was the absolute dominant bacterial species across developmental stages in and we confirmed that lacks also in the immature stages, and had mostly Mollicutes bacteria in the adult worker guts. in appeared to be transovarially transmitted similar to transmission in solitary insects. In contrast, Mollicutes were socially transmitted from old workers to newly emerged callows. We found that larval and pupal guts of both ant species contained and bacteria that are also found in fungus gardens, but hardly or not in adult workers, suggesting they are beneficial only for larval growth and development. Our results reveal that transmission pathways for bacterial symbionts may be very different both between developmental stages and between sister genera and that identifying the mechanisms of bacterial acquisition and loss will be important to clarify their putative mutualistic functions.
社会性膜翅目昆虫具有明显的幼虫和成虫阶段，由变态发育分隔，这意味着在蛹期其外部和内部身体结构会发生显著重塑。这给肠道共生体带来了挑战，因为现有的菌群会消失，可能需要也可能不需要被取代。为了阐明变态发育对细菌与宿主之间关联的中断程度，我们分析了发育过程中肠道微生物群的变化，并追踪了切叶蚁属的两种切叶蚁（它们都是新大陆热带地区重要的功能性食草动物）从卵到成虫阶段优势共生体的传播途径。在Atta的发育阶段中，细菌密度保持相似，但Acromyrmex蚁群的细菌患病率非常低，这表明肠道细菌共生体没有得到积极维持。我们发现，在Atta的各个发育阶段，Actinobacteria都是绝对优势细菌物种，并且我们证实，在未成熟阶段Acromyrmex也缺乏Actinobacteria，其成年工蚁肠道中主要是柔膜菌纲细菌。Atta中的Actinobacteria似乎是通过卵传递的，类似于独居昆虫中的传播方式。相比之下，柔膜菌纲细菌是通过社会传播从老工蚁传递给新羽化的幼蚁。我们发现，这两种蚂蚁的幼虫和蛹肠道中都含有在菌圃中也能发现的Bifidobacterium和Actinobacteria细菌，但在成年工蚁中很少或没有，这表明它们仅对幼虫的生长发育有益。我们的结果表明，细菌共生体的传播途径在发育阶段之间以及姐妹属之间可能非常不同，并且确定细菌获取和丧失的机制对于阐明它们假定的互利功能将非常重要。
