Data_Sheet_1_Nutrient-Poor Breeding Substrates of Ambrosia Beetles Are Enriched With Biologically Important Elements.xlsx

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, Xyleborinus saxesenii (Scolytinae: Xyleborini), Trypodendron lineatum (Scolytinae: Xyloterini) and Elateroides dermestoides (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 X. saxesenii, followed by T. lineatum and E. dermestoides, 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.

在树木木质部腔室中营生的真菌栽培现象在至少十二个象甲科（Curculionidae: Scolytinae, Platypodinae）的亚科和一种木质长蠹科（Lymexylidae）的世系中独立演化。这些世系共同被称为寄食甲虫，因其积极培育营养丰富的“寄食真菌”作为其主要食物来源。这些甲虫对其寄食真菌的依赖性为绝对，后者为其提供了广泛必需的营养成分，确保其在极端贫瘠的环境中生存。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氮（N）、磷（P）、硫（S）、钾（K）、钙（Ca）、镁（Mg）和锰（Mn）等元素，其浓度却极低。目前尚未测试过寄食甲虫及其真菌如何在这样的生境中满足其营养需求。本研究旨在首次确定寄食甲虫的腔室是否通常富含在未被占领的木质部组织中稀缺的元素，以及这些营养素是否由真菌伙伴通过木质部输送到腔室中。为此，我们考察了来自三个独立演化栽培世系的三个寄食甲虫物种的自然腔室，包括Xyleborinus saxesenii（象甲科：Xyleborini）、Trypodendron lineatum（象甲科：Xyloterini）和Elateroides dermestoides（木质长蠹科），它们分别栽培属于子囊菌纲的Ophiostomatales、Microascales和Saccharomycetales类群的无关寄食真菌。在甲虫的腔室内，尤其是钙（Ca）、氮（N）、磷（P）、钾（K）、镁（Mg）、锰（Mn）和硫（S）等元素，其浓度较高，而在周围的木质部中则含量极低。元素的浓度通常以X. saxesenii为最高，其次是T. lineatum和E. dermestoides，这与其每腔室的社群度和产卵量呈正相关。我们提出，寄食真菌共生体通过其菌丝将必需元素从木质部转移到其在腔室壁上形成的子实体结构。此外，观察到的极强富集现象表明，这些元素可能从昆虫的排泄物中回收，其中细菌和酵母可能发挥作用。