Microbiom analysis of: "Habitat Quality Determines Dispersal Decisions and Fitness in a Beetle – Fungus Mutualism."

Front. Ecol. Evol. 9:602672. doi: 10.3389/fevo.2021.602672 Delayed dispersal of sexually mature offspring is a fundamental component of cooperative breeding. In ambrosia beetles, female offspring temporarily remain in their natal nest and refrain from reproduction, instead investing in alloparental care. Previouswork has demonstrated a link between helping behaviour and the increased need for pathogen defence arising from their close association with fungal cultivars. In the ambrosia beetle Xyleborinus saxesenii, mature female offspring can effectively fightpathogen infections and manage the microbial composition within the nest by adjusting the frequency of different hygienic and nest maintenance behaviours. This suggests a potential to respond flexibly to the ecology of their nest, which calls for a betterunderstanding of the connection between behaviour and the microbial community thriving within their nests. Here, we studied the significance of the mutualistic fungus garden composition for the beetles' nest ecology and fitness by experimentally varying substrate quality. We found that the vertically transmitted ambrosia fungus garden is composed of at least two fungus mutualist species and a wide variety of other microbes varying in their relative abundance. This is strongly affected by the moisture contentof the substrate, which in nature depends on the age and type of wood. We found that the mutualist fungi complement each other in terms of dryness-resistance, allowing the beetles to utilise a broad range of substrates over prolonged time during which the wood gradually desiccates. Under suboptimal humidity conditions, the interaction between host and multiple fungus species has important ramifications for the behaviour of philopatric helpers, including their alloparental investment, sibling cannibalism and the timing of dispersal. Rearing five generations of beetles consecutively in dry substrate resulted in transgenerational effects on philopatry and alloparental care, probably mediated through the dominance of a particular fungus species that was driven by the experimental habitat condition. Interestingly, the nests of these selection lines produced much more offspring after five generations than any first-generation nest, which may have reflected increased egg laying by non-dispersing daughters. Our study highlights the importance of considering the interactions between the microbial community andtheir insect hosts for understanding social evolution in cooperatively breeding beetles.

《生态学与进化前沿》（Frontiers in Ecology and Evolution）第9卷，文章编号602672，DOI：10.3389/fevo.2021.602672。性成熟后代的延迟扩散是合作育幼（cooperative breeding）的核心特征。在食菌小蠹（ambrosia beetles）中，雌性后代会暂时停留在出生地巢穴中，放弃自身繁殖，转而投入异亲抚育（alloparental care）行为。既往研究表明，协助行为与因与真菌栽培种紧密共生而升高的病原体防御需求之间存在关联。在萨克斯氏星坑小蠹（Xyleborinus saxesenii）中，性成熟的雌性后代可通过调节不同卫生行为与巢穴维护行为的频率，有效抵御病原体感染并调控巢穴内的微生物群落组成。这一发现提示它们具备灵活响应巢穴生态的潜力，也要求我们更深入地解析行为与巢穴内繁盛的微生物群落之间的关联。
本研究通过实验调控基质质量，探究了共生真菌群落组成对小蠹虫巢穴生态与适合度（fitness）的重要意义。研究发现，垂直传播的食菌真菌群落至少包含两种真菌共生种，以及大量相对丰度各异的其他微生物；该群落组成受基质含水量的强烈影响，而在自然环境中，基质含水量取决于木材的树龄与材质。
研究还发现，共生真菌在抗干燥能力上相互补充，使得小蠹虫能够在木材逐渐干燥的较长周期内，利用多种不同类型的基质。在亚适宜湿度条件下，宿主与多种真菌物种之间的互作对留居协助者的行为具有重要影响，包括其异亲抚育投入、同类相食行为以及扩散时机。
在干燥基质中连续饲养五代小蠹虫，会对其留居行为与异亲抚育产生跨代效应，这一效应可能由实验生境条件驱动下的特定真菌物种优势所介导。有趣的是，经过五代选育的种群巢穴所产生的后代数量远多于任何第一代巢穴，这可能源于不扩散的雌性后代产卵量提升。
本研究强调，若要理解合作育幼小蠹虫的社会演化，需纳入微生物群落与昆虫宿主之间的互作关系进行考量。