Ecological speciation of Japanese hedgehog mushroom: Hydnum subalpinum sp. nov. is distinguished from its sister species H. repando-orientale by means of integrative taxonomy

Hydnum repando-orientale is an East Asian species closely related to H. boreorepandum and H. repandum ; all three species produce edible mushrooms. We identified two ecological groups of H. repando-orientale in Japan: a temperate group occurring in Fagaceae-dominated forest at < 1200 m a.s.l. (ROF) and a subalpine group occurring in coniferous forest in highland at > 1900 m a.s.l. (ROC). We re-examined the taxonomy of the two ecological groups of H. repando-orientale using integrative approaches. Phylogenies of the two ecological groups and other related species were inferred from the internal transcribed spacer (ITS) and gene portions encoding the large subunit of nc rRNA (LSU), translation elongation factor-1 alpha ( TEF1 ), RNA polymerase II largest subunit ( RPB1 ), and RNA polymerase II second-largest subunit ( RPB2 ). The concatenated phylogenetic tree separated the two ecological groups into well-supported sister clades. Also, species delimitations based on the topological congruence (GCPSR) and coalescent models (GMYC and BP&P) supported to separate the two ecological groups. Morphological analysis showed that ROC specimens had significantly larger basidiospores, compared with ROF specimens. Mon-mon mating tests using six ROF, three ROC, and three H. boreorepandum strains each showed independent incompatible groups, whereas one ROC strain showed compatibility with both ROC and ROF populations. Based on these results, we defined the ROC group as a new species, H. subalpinum . Because H. repando-orientale and H. subalpinum have smaller genetic divergence in nc rDNA and maintain slight sexual compatibility, they may have recently speciated in East Asia.