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

在甲虫和树皮甲虫及其特定种类的丝状真菌之间严格的义务互惠关系的起源是这些甲虫进化的里程碑之一。这两种昆虫目前在世界范围内共有3500多种，它们侵害各种类型的树木，对全球的森林和种植园造成重大经济损失。这种共生真菌在凤仙花和树皮甲虫的生活中扮演着多种重要角色，例如，在营养贫乏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，这些真菌共生体的保护和运输对甲虫寄主的生存至关重要，特别是在滞育和扩散飞行过程中。所有的仙甲虫和一些树皮甲虫都有菌丝体，这是一种专门的结构，用于将互惠真菌从一个巢穴或画廊传播到另一个巢穴或画廊。几十年来，人们知道菌丝体只含有特定的共生真菌，没有其他微生物。然而，我们对这种选择性的原因知之甚少，也不知道菌丝体是否也提供营养并调节其真菌货物的生长。本项目旨在运用化学、微生物学和超微结构的方法，试图回答一些古老的问题，在ambrosia和树皮甲虫菌丝体研究。我们将通过提供必需的营养物质来研究菌丝体对传播真菌生长的影响。虽然据描述，菌丝体中只有共生真菌，但我们的初步证据表明，细菌的存在可能会固定氮。这些细菌能显著提高木材和树皮基质的低氮含量，从而提高甲虫的适应度。最后，我们将寻找抗菌化合物，这些化合物可能负责长期描述的菌丝体选择性，使互惠真菌能够胜过无处不在的拮抗微生物。通过建立菌丝体的新功能，我们的工作将为推动ambrosia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于限制这些昆虫对世界各地的森林和人工林造成的广泛损害。

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.