AUTHOR=Zhang Rui , Shi Xiao-fei , Liu Pei-gui , Wilson Andrew W. , Mueller Gregory M. 

TITLE=Host Shift Speciation of the Ectomycorrhizal Genus Suillus (Suillineae, Boletales) and Biogeographic Comparison With Its Host Pinaceae

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.831450

DOI=10.3389/fmicb.2022.831450

ISSN=1664-302X

ABSTRACT=<p><italic>Suillus</italic> is a genus of ectomycorrhizal fungi associated almost exclusively with Pinaceae. Lack of sample collections in East Asia and unresolved basal phylogenetic relationships of the genus are the major obstacles for better understanding the <italic>Suillus</italic> evolution. A resolved phylogeny of <italic>Suillus</italic> representing global diversity was achieved by sequencing multiple nuclear ribosomal and protein coding genes and extensive samples collected in East Asia. Fungal fossils are extremely rare, and the Eocene ectomycorrhizal symbiosis (ECM) fossil of <italic>Pinus</italic> root has been widely used for calibration. This study explored an alternative calibration scenario of the ECM fossil for controversy. Ancestral host associations of <italic>Suillus</italic> were estimated by maximum likelihood and Bayesian Markov chain Monte Carlo (MCMC) analyses, inferred from current host information from root tips and field observation. Host shift speciation explains the diversification of <italic>Suillus</italic> major clades. The three basal subgenera of <italic>Suillus</italic> were inferred to be associated with <italic>Larix</italic>, and diverged in early Eocene or Upper Cretaceous. In the early Oligocene or Paleocene, subgenus <italic>Suillus</italic> diverged and switched host to <italic>Pinus</italic> subgenus <italic>Strobus</italic>, and then switched to subgenus <italic>Pinus</italic> four times. <italic>Suillus</italic> subgenus <italic>Douglasii</italic> switched host from <italic>Larix</italic> to <italic>Pseudotsuga</italic> in Oligocene or Eocene. Increased species diversity occurred in subgenus <italic>Suillus</italic> after it switched host to <italic>Pinus</italic> but no associated speciation rate shifts were detected. Ancestral biogeographic distributions of <italic>Suillus</italic> and Pinaceae were estimated under the Dispersal Extinction Cladogenesis (DEC) model. Ancestral distribution patterns of <italic>Suillus</italic> and Pinaceae are related but generally discordant. Dispersals between Eurasia and North America explain the prevalence of disjunct <italic>Suillus</italic> taxa.</p>