Lehenberger Maximilian, Benkert Markus, Biedermann Peter H W
Research Group Insect-Fungus Symbiosis, Department of Animal Ecology and Tropical Biology, University of Würzburg, Würzburg, Germany.
Chair of Forest Entomology and Protection, University of Freiburg, Freiburg im Breisgau, Germany.
Front Microbiol. 2021 Jan 13;11:590111. doi: 10.3389/fmicb.2020.590111. eCollection 2020.
Bark beetles () colonize woody tissues like phloem or xylem and are associated with a broad range of micro-organisms. Specific fungi in the ascomycete orders Hypocreales, Microascales and Ophistomatales as well as the basidiomycete Russulales have been found to be of high importance for successful tree colonization and reproduction in many species. While fungal mutualisms are facultative for most phloem-colonizing bark beetles (), xylem-colonizing ambrosia beetles are long known to obligatorily depend on mutualistic fungi for nutrition of adults and larvae. Recently, a defensive role of fungal mutualists for their ambrosia beetle hosts was revealed: Few tested mutualists outcompeted other beetle-antagonistic fungi by their ability to produce, detoxify and metabolize ethanol, which is naturally occurring in stressed and/or dying trees that many ambrosia beetle species preferentially colonize. Here, we aim to test (i) how widespread beneficial effects of ethanol are among the independently evolved lineages of ambrosia beetle fungal mutualists and (ii) whether it is also present in common fungal symbionts of two bark beetle species (, ) and some general fungal antagonists of bark and ambrosia beetle species. The majority of mutualistic ambrosia beetle fungi tested benefited (or at least were not harmed) by the presence of ethanol in terms of growth parameters (e.g., biomass), whereas fungal antagonists were inhibited. This confirms the competitive advantage of nutritional mutualists in the beetle's preferred, ethanol-containing host material. Even though most bark beetle fungi are found in the same phylogenetic lineages and ancestral to the ambrosia beetle () fungi, most of them were highly negatively affected by ethanol and only a nutritional mutualist of benefited, however. This suggests that ethanol tolerance is a derived trait in nutritional fungal mutualists, particularly in ambrosia beetles that show cooperative farming of their fungi.
小蠹虫会在韧皮部或木质部等木质组织中定殖，并与多种微生物相关联。已发现肉座菌目、小囊菌目和长喙壳目子囊菌纲以及红菇目担子菌纲中的特定真菌，对许多物种成功定殖树木和繁殖至关重要。虽然真菌共生关系对大多数在韧皮部定殖的小蠹虫来说是兼性的，但长期以来已知在木质部定殖的食菌小蠹虫在成虫和幼虫营养方面完全依赖共生真菌。最近，发现真菌共生体对其食菌小蠹虫宿主具有防御作用：少数经过测试的共生体通过产生、解毒和代谢乙醇的能力，胜过其他与甲虫拮抗的真菌，乙醇天然存在于许多食菌小蠹虫优先定殖的受胁迫和/或濒死树木中。在此，我们旨在测试（i）乙醇的有益作用在食菌小蠹虫真菌共生体的独立进化谱系中分布有多广泛，以及（ii）它是否也存在于两种小蠹虫物种（……）的常见真菌共生体以及一些小蠹虫和食菌小蠹虫物种的一般真菌拮抗剂中。大多数经过测试的食菌小蠹虫共生真菌在生长参数（如生物量）方面因乙醇的存在而受益（或至少未受损害），而真菌拮抗剂则受到抑制。这证实了营养共生体在甲虫偏好的含乙醇宿主材料中的竞争优势。尽管大多数小蠹虫真菌存在于相同的系统发育谱系中，且是食菌小蠹虫（……）真菌的祖先，但它们中的大多数受到乙醇的负面影响很大，然而只有…… 的一种营养共生体受益。这表明乙醇耐受性是营养真菌共生体中的一种衍生特征，特别是在对其真菌表现出合作培育行为的食菌小蠹虫中。
