Lehenberger Maximilian, Foh Nina, Göttlein Axel, Six Diana, 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 Apr 26;12:664542. doi: 10.3389/fmicb.2021.664542. eCollection 2021.
Fungus-farming within galleries in the xylem of trees has evolved independently in at least twelve lineages of weevils (Curculionidae: Scolytinae, Platypodinae) and one lineage of ship-timber beetles (Lymexylidae). Jointly these are termed ambrosia beetles because they actively cultivate nutritional "ambrosia fungi" as their main source of food. The beetles are obligately dependent on their ambrosia fungi as they provide them a broad range of essential nutrients ensuring their survival in an extremely nutrient-poor environment. While xylem is rich in carbon (C) and hydrogen (H), various elements essential for fungal and beetle growth, such as nitrogen (N), phosphorus (P), sulfur (S), potassium (K), calcium (Ca), magnesium (Mg), and manganese (Mn) are extremely low in concentration. Currently it remains untested how both ambrosia beetles and their fungi meet their nutritional requirements in this habitat. Here, we aimed to determine for the first time if galleries of ambrosia beetles are generally enriched with elements that are rare in uncolonized xylem tissue and whether these nutrients are translocated to the galleries from the xylem by the fungal associates. To do so, we examined natural galleries of three ambrosia beetle species from three independently evolved farming lineages, (Scolytinae: Xyleborini), (Scolytinae: Xyloterini) and (Lymexylidae), that cultivate unrelated ambrosia fungi in the ascomycete orders Ophiostomatales, Microascales, and Saccharomycetales, respectively. Several elements, in particular Ca, N, P, K, Mg, Mn, and S, were present in high concentrations within the beetles' galleries but available in only very low concentrations in the surrounding xylem. The concentration of elements was generally highest with , followed by and , which positively correlates with the degree of sociality and productivity of brood per gallery. We propose that the ambrosia fungal mutualists are translocating essential elements through their hyphae from the xylem to fruiting structures they form on gallery walls. Moreover, the extremely strong enrichment observed suggests recycling of these elements from the feces of the insects, where bacteria and yeasts might play a role.
在树木木质部的虫道内培育真菌的行为，在至少12个象鼻虫谱系（象鼻虫科：小蠹亚科、长小蠹亚科）和1个船木甲虫谱系（长蠹科）中独立进化而来。这些统称为食菌小蠹，因为它们积极培育营养丰富的“共生真菌”作为主要食物来源。这些甲虫完全依赖于它们的共生真菌，因为真菌为它们提供了广泛的必需营养物质，确保它们在营养极度匮乏的环境中生存。虽然木质部富含碳（C）和氢（H），但对于真菌和甲虫生长至关重要的各种元素，如氮（N）、磷（P）、硫（S）、钾（K）、钙（Ca）、镁（Mg）和锰（Mn），其浓度极低。目前尚不清楚食菌小蠹及其真菌如何在这种栖息地满足它们的营养需求。在这里，我们旨在首次确定食菌小蠹的虫道是否普遍富含未被侵染的木质部组织中稀有的元素，以及这些营养物质是否通过真菌共生体从木质部转运到虫道中。为此，我们研究了来自三个独立进化的培育谱系的三种食菌小蠹的天然虫道，分别是（小蠹亚科：材小蠹族）、（小蠹亚科：木小蠹族）和（长蠹科），它们分别在子囊菌纲的长喙壳目、微囊菌目和酵母目中培育不同的共生真菌。几种元素，特别是钙（Ca）、氮（N）、磷（P）、钾（K）、镁（Mg）、锰（Mn）和硫（S），在甲虫的虫道中浓度很高，但在周围的木质部中浓度极低。元素浓度通常以最高，其次是和，这与每个虫道中社会性和繁殖力的程度呈正相关。我们认为，共生真菌通过它们的菌丝将必需元素从木质部转运到它们在虫道壁上形成的子实体结构中。此外，观察到的极强富集现象表明这些元素是从昆虫粪便中循环而来的，细菌和酵母可能在其中发挥了作用。
