Evolutionary histories of soil fungi are reflected in their large-scale biogeography.

Although fungal communities are known to vary along latitudinal gradients, mechanisms underlying this pattern are not well-understood. We used high-throughput sequencing to examine the large-scale distributions of soil fungi and their relation to evolutionary history. We tested the Tropical Conservatism Hypothesis, which predicts that ancestral fungal groups should be more restricted to tropical latitudes and conditions than would more recently derived groups. We found support for this hypothesis in that older phyla preferred significantly lower latitudes and warmer, wetter conditions than did younger phyla. Moreover, preferences for higher latitudes and lower precipitation levels were significantly phylogenetically conserved among the six younger phyla, possibly because the older phyla possess a zoospore stage that is vulnerable to drought, whereas the younger phyla retain protective cell walls throughout their life cycle. Our study provides novel evidence that the Tropical Conservatism Hypothesis applies to microbes as well as plants and animals.