Data from: Is the switch to an ectomycorrhizal state an evolutionary key innovation in mushroom-forming fungi? A case study in the Tricholomatineae (Agaricales)

Although fungi are one of the most diverse groups of organisms, little is known about the processes that shape their high taxonomic diversity. This study focuses on evolution of ectomycorrhizal (ECM) fungi, symbiotic associates of many trees and shrubs, in the suborder Tricholomatineae of the Agaricales. We used the BiSSE model and BAMM to test the hypothesis that the ECM habit represents an evolutionary key innovation that allowed the colonization of new niches followed by an increase in diversification rate. Ancestral state reconstruction supports the ancestor of the Tricholomatineae as non-ECM. We detected two diversification rate increases in the genus Tricholoma and the Rhodopolioid clade of the genus Entoloma. However, no increases in diversification were detected in the four other ECM clades of Tricholomatineae. We suggest that diversification of Tricholoma was not only due to the evolution of the ECM lifestyle, but to the expansion and dominance of its main hosts and ability to associate with a variety of hosts. Diversification in the Rhodopolioid clade could be due to the unique combination of spore morphology and ECM habit. The spore morphology may represent an exaptation that aided spore dispersal and colonization. This is the first study to investigate rate shifts across a phylogeny that contains both non-ECM and ECM lineages.

尽管真菌是物种多样性最为丰富的生物类群之一，但目前学界对塑造其极高分类多样性的演化机制仍知之甚少。本研究聚焦于伞菌目（Agaricales）口蘑亚目（Tricholomatineae）类群中的外生菌根（ectomycorrhizal, ECM）真菌——一类与多数树木、灌木形成共生关系的微生物——的演化历程。本研究采用BiSSE模型与BAMM工具，验证了如下假说：外生菌根共生习性是一项演化关键创新，可使真菌得以开拓全新生态位并提升物种分化速率。祖先状态重建结果显示，口蘑亚目的共同祖先并非外生菌根共生型真菌。我们在口蘑属（Tricholoma）以及粉褶蕈属（Entoloma）的红孢蕈演化支（Rhodopolioid clade）中，各检测到一次物种分化速率的提升事件，但在口蘑亚目其余4个外生菌根演化支中，并未观测到类似的分化速率显著提升。我们推测，口蘑属的物种分化不仅源于外生菌根共生生活方式的演化，还与其宿主类群的扩张与主导地位，以及该属真菌与多种宿主建立共生关系的能力密切相关；而红孢蕈演化支的物种分化，则可能源于孢子形态与外生菌根共生习性的独特组合。其孢子形态或属于一种预适应（exaptation）特征，有助于孢子传播与宿主定植。本研究是首个针对同时包含非外生菌根与外生菌根演化支的系统发育树开展分化速率漂移研究的学术工作。