Abstract
Pakaraimaea dipterocarpacea, a member of the Dipterocarpaceae endemic in the Guayana region, is associated with a diverse community of ectomycorrhizal (ECM) fungi. Amongst the 41 ECM fungal species detected in a 400 m2 P. dipterocarpacea ssp. nitida plot in Southern Venezuela, three species belonged to the Sebacinales. We tested whether ECM anatomotype characterization can be used as a feasible element in an integrative taxonomy in this diverse fungal group, where the relevance of fruitbody morphology for species delimitation seems limited. Using a combination of ECM morpho-anatomical characterizations and phylogenetic analyses based on nuclear ITS and LSU sequences, we report three new species. The main distinguishing features of Sebacina guayanensis are the yellowish cell walls together with conspicuous undifferentiated, uniform compact (type B) rhizomorphs. Staghorn-like hyphae are characteristic of S. tomentosa. The combination of clusters of thick-walled emanating hyphae, including hyphae similar to awl-shaped cystidia with basal dichotomous or trichotomous ramifications, and the presence of type B rhizomorphs were characteristic of a third, yet unnamed species. The three species belong to three different, possibly specifically tropical clades in Sebacinales Group A. The geographic distribution of phylogenetically related strains was wide, including a Dicymbe forest in Guyana and an Ecuadorian rainforest with Coccoloba species. We show that ECM morpho-anatomy can be used, in combination with other analyses, to delineate species within Sebacinales Group A. In addition to phylogenetic information, type B rhizomorphs observed in different Sebacinales clades have important ecological implications for this fungal group. The phylogeography of Sebacinales suggests that dispersion and host jump are important radiation mechanisms that shaped P. dipterocarpacea ECM fungal community. This study emphasizes the need for more sequence data to evaluate the hypothesis that phylogeographic relationships between neo- and paleotropical ECM fungal species could be attributed to the vicariance of cross-continental hosts such as the Dipterocarpacae.
Highlights
Sebacinales is a genetically diverse group of basidiomycetes with a broad range of lifestyles including a diversity of mycorrhizal and endophytic associations [1]
The additional observation of an African-only clade indicates that Sebacinales Group A strains, with no closely related temperate species, may have diversified both in the neo- and the paleotropics
The observation of tropical-only clades for the first time in the present study may be attributable to a greater sampling of tropical ECM Sebacinales sequences in our datasets
Summary
Sebacinales is a genetically diverse group of basidiomycetes with a broad range of lifestyles including a diversity of mycorrhizal and endophytic associations [1]. Pakaraimaea dipterocarpacea, an endemic tree species from the Guayana region [11,16,17], is one of the few known locally dominant ECM tree species in the neotropical lowland forests This tree belongs to the Dipterocarpaceae, one of the most important ECM tropical tree family in SE Asia [18]. ECM fungal DNA comparisons between forests in the Guayana region and a molecular phylogenetic analysis of two newly reported Inocybe species [12,15] suggested that host jump and fungal dispersion, i.e., long-distance dispersal across a pre-existing barrier [23], were important radiation mechanisms involved in shaping the fungal community of P. dipterocarpacea [12]. Dipterocarpacea Sebacinales species were analyzed with a broad array of taxa including Sebacinales strains collected worldwide
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