A selective fungal transport organ (mycangium) maintains coarse phylogenetic congruence between fungus-farming ambrosia beetles and their symbionts

Thousands of species of ambrosia beetles excavate tunnels in wood to farm fungi. They maintain associations with particular lineages of fungi, but the phylogenetic extent and mechanisms of fidelity are unknown. We test the hypothesis that selectivity of their mycangium enforces fidelity at coarse phylogenetic scales, while permitting promiscuity among closely related fungal mutualists. We confirm a single evolutionary origin of the Xylosandrus complex – a group of several xyleborine genera that farm fungi in the genus Ambrosiella. Multi-level co-phylogenetic analysis revealed frequent symbiont switching within major Ambrosiella clades, but not between clades. The loss of the mycangium in Diuncus, a genus of evolutionary cheaters, was commensurate with loss of fidelity to fungal clades, supporting the hypothesis that the mycangium reinforces fidelity. Finally, in-vivo experiments tracked symbiotic compatibility throughout the symbiotic life cycle of Xylosandrus compactus and demonstrated...

数千种食菌小蠹（ambrosia beetles）会在木材中挖掘坑道以培育真菌。它们与特定真菌演化支形成共生关系，但目前学界对这种共生专一性的系统发育范围及其作用机制仍不清楚。我们提出假说：食菌小蠹的菌囊（mycangium）选择性会在粗尺度系统发育层面强化共生专一性，同时允许其与近缘的共生真菌间存在一定的混杂共生关系。我们证实了双棘小蠹复合群（Xylosandrus complex）的单一演化起源——该类群包含多个材小蠹类属，其共生真菌均属于食菌霉属（Ambrosiella）。多维度协同系统发育分析显示，食菌霉属主要演化支内部频繁发生共生体切换现象，但演化支之间并未出现此类切换。离蠹属（Diuncus）作为一类演化欺骗型小蠹，其菌囊的丢失与对真菌演化支专一性的丧失相吻合，这一结果支持了菌囊可强化共生专一性的假说。最后，我们通过体内实验追踪了致密双棘小蠹（Xylosandrus compactus）整个共生生命周期中的共生兼容性，并证实了……