High speciation rate at temperate latitudes explains unusual diversity gradients in a clade of ectomycorrhizal fungi

Understanding the patterns of biodiversity through time and space is a challenging task. However, phylogeny-based macroevolutionary models allow us to account and measure many of the processes responsible for diversity build-up, namely speciation and extinction. The general latitudinal diversity gradient (LDG) is a well-recognized pattern describing a decline in species richness from the equator pole-wards. Recent macroecological studies in ectomycorrhizal (EM) fungi have shown that their LDG is shifted, peaking at temperate rather than tropical latitudes. Here we investigate this phenomenon from a macroevolutionary perspective, focusing on a well-sampled group of edible EM edible mushrooms from the genus Amanita -the Caesar's mushrooms, which follow similar diversity patterns. Our approach consisted in applying a suite of models including: (1) non-trait-dependent time-varying diversification (BAMM), (2) continuous trait-dependent diversification (QuaSSE), and (3) diversity-dependent diversification (DDD). In short, results give strong support for high speciation rates at temperate latitudes (BAMM and QuaSSE). We also find some evidence for different diversity-dependence thresholds in 'temperate' and 'tropical' subclades, and little differences in diversity due to extinction. We conclude that our analyses on the Caesar's mushrooms give further evidence of a temperate-peaking LDG in EM fungi, highlighting the importance and the implications of macroevolutionary processes in explaining diversity gradients in microorganisms. This article is protected by copyright. All rights reserved.