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.