Take good care of my fungi - The role of mycetangia in facilitating fungal spore transmission in fungus-farming bark and ambrosia beetles

文心兰和树皮甲虫及其特有的丝状真菌之间严格的专有互惠关系的起源是这些甲虫进化过程中的里程碑之一。这两类昆虫目前在世界范围内包括3500多个物种，它们侵扰着各种类型的树木，并对全球的森林和种植园造成重大经济破坏。互惠真菌在文心兰和树皮甲虫的生活中扮演着多种重要角色，例如，在营养不良的环境中作为营养来源，以及作为树木化学防御的解毒剂。因此，保护和运输这些真菌共生体，对于它们的甲虫宿主的生存至关重要，特别是在滞育和分散飞行期间。所有的文心果甲虫和一些树皮甲虫都有霉菌，这是一种特殊的结构，用于将互惠共生的真菌从一个巢或走廊传播到新的巢或廊。几十年来，人们一直知道霉菌只含有特定的互惠真菌，而没有其他微生物。然而，我们对这种选择性的原因以及霉菌是否也提供营养和调节真菌货物的生长知之甚少。该项目旨在使用化学、微生物学和超微结构方法，试图回答文心果和树皮甲虫研究中一些最古老的问题。我们将通过提供必需的营养来研究霉菌对传播真菌生长的影响。虽然霉菌被描述为只含有互惠共生的真菌，但我们的初步证据表明，存在可能固定氮的细菌。这类细菌能显著提高木材和树皮基质的低氮含量，从而提高甲虫的适合度。最后，我们将寻找可能导致长期描述的霉菌选择性的抗微生物化合物，使互惠真菌能够击败无处不在的拮抗微生物。通过建立Mycetangia的新功能，我们的工作将为推动文心兰和树皮甲虫成功的因素提供新的见解。这些知识最终可以用来限制这些昆虫对世界各地的森林和树木种植园造成的广泛破坏。

The origin of a strict obligate mutualism between ambrosia and bark beetles and their species-specific filamentous fungi was one of the milestones in the evolution of these beetles. These two insect groups currently encompass more than 3,500 species worldwide infesting various types of trees and causing major economic damage to forests and plantations around the globe. The mutualistic fungi play multiple essential roles in the lives of ambrosia and bark beetles, for example, as a source of nutrition within an otherwise nutrient-poor environment and as detoxifiers of tree chemical defenses. Therefore, the protection and transport of these fungal symbionts, is of crucial importance for the survival of their beetle hosts, especially during diapause and dispersal flight. All ambrosia beetles and some bark beetles possess mycetangia, specialized structures for the transmission of mutualistic fungi from one nest or gallery to a new one. For decades, mycetangia have been known to harbor only specific mutualist fungi and no other microbes. However, we know little about what is responsible for this selectivity and whether mycetangia also provide nutrition and regulate the growth of their fungal cargo. This project aims to employ chemical, microbiological and ultrastructural methods to try to answer some of the oldest questions in ambrosia and bark beetle mycetangia research. We will examine the impact of mycetangia on the growth of transmitted fungi by providing essential nutrients. Although mycetangia were described to harbor only mutualistic fungi, our preliminary evidence suggests the presence of bacteria that may fix nitrogen. Such bacteria could significantly increase the low nitrogen content of wood and bark substrates, and thus improve beetle fitness. Finally, we will search for antimicrobial compounds that could be responsible for the long-described selectivity of mycetangia allowing the mutualistic fungus to outcompete ubiquitous antagonistic microbes. By establishing new functions for mycetangia, our work will provide fresh insights into the factors driving the success of ambrosia and bark beetles. Such knowledge could eventually be applied to limit the extensive damage caused by these insects to forests and tree plantations throughout the world.