Data from: Into and out of the tropics: global diversification patterns in a hyper-diverse clade of ectomycorrhizal fungi

Ectomycorrhizal (ECM) fungi, symbiotic mutualists of many dominant tree and shrub species, exhibit a biogeographic pattern counter to the established latitudinal diversity gradient of most macroflora and fauna. However, an evolutionary basis for this pattern has not been explicitly tested in a diverse lineage. In this study, we reconstructed a mega-phylogeny of a cosmopolitan and hyper-diverse genus of ECM fungi, Russula, sampling from annotated collections and utilizing publically available sequences deposited in GenBank. Metadata from molecular operational taxonomic unit cluster sets were examined to infer the distribution and plant association of the genus. This allowed us to test for differences in patterns of diversification between tropical and extratropical taxa, as well as how their associations with different plant lineages may be a driver of diversification. Results show that Russula is most species-rich at temperate latitudes and ancestral state reconstruction shows that the genus initially diversified in temperate areas. Migration into and out of the tropics characterizes the early evolution of the genus, and these transitions have been frequent since this time. We propose the ‘generalized diversification rate’ hypothesis to explain the reversed latitudinal diversity gradient pattern in Russula as we detect a higher net diversification rate in extratropical lineages. Patterns of diversification with plant associates support host switching and host expansion as driving diversification, with a higher diversification rate in lineages associated with Pinaceae and frequent transitions to association with angiosperms.

外生菌根（Ectomycorrhizal, ECM）真菌作为众多优势乔灌木物种的共生互惠伙伴，呈现出与绝大多数大型动植物既定纬度多样性梯度相悖的生物地理格局。然而，这一格局的演化基础尚未在多样演化支系中得到明确检验。本研究针对世界广布且高度多样的外生菌根真菌属——红菇属（Russula）构建了超级系统发育树，采样自经注释的馆藏标本，并利用基因库（GenBank）中公开收录的序列数据。通过分析分子操作分类单元（molecular operational taxonomic unit, MOTU）聚类集的元数据，我们推断了该属的分布格局与植物共生关联。借此，我们得以检验热带与非热带类群的分化模式差异，以及其与不同植物演化支系的共生关系是否为分化的驱动因素。研究结果显示，红菇属在温带纬度区域物种丰富度最高；祖先状态重建结果表明，该属最初于温带区域发生分化。该属的早期演化以往返热带的迁移事件为特征，且自该时期以来此类转换始终频繁发生。鉴于我们检测到非热带类群具有更高的净分化速率，我们提出“广义分化速率假说”以解释红菇属中反向纬度多样性梯度的格局。与植物共生伙伴相关的分化模式支持宿主切换与宿主扩张为分化驱动因素，且与松科（Pinaceae）共生的类群分化速率更高，向被子植物共生关系的转换事件同样频繁。