How to resolve cryptic species of polypores: an example in Fomes

Abstract

Species that cannot be easily distinguished based on morphology, but which form distinct phylogenetic lineages based on molecular markers, are often referred to as cryptic species. They have been proposed in a number of fungal genera, including the basidiomycete genus Fomes. The main aim of this work was to test new methods for species delimitation in cryptic lineages of polypores, and to define useful characters for species identification. A detailed examination of a number of different Fomes strains that had been collected and isolated from different habitats in Italy and Austria confirmed the presence of distinct lineages in the Fomes fomentarius clade. Our zero hypothesis was that the Mediterranean strains growing on Quercus represent a species which can be delimited based on morphological and physiological characters when they are evaluated in statistically relevant numbers. This hypothesis was tested based on phylogenetic analysis of the rDNA ITS region, morphological characters of basidiomes and pure cultures, growth rates and optimum growth temperature experiments, mycelial confrontation tests, enzyme activity tests and volatile organic compound (VOC) production. The Mediterranean lineage can unambiguously be delimited from F. fomentarius. A syntype of an obscure and previously synonymized name, Polyporus inzengae, represents the Mediterranean lineage that we recognize as Fomes inzengae, a distinct species. The rDNA ITS region is useful for delimitation of Fomes species. Moreover, also a variety of morphological characters including hymenophore pore size, basidiospore size, and diameter of skeletal hyphae are useful delimiting characters. The ecology is also very important, because the plant host appears to be a central factor driving speciation. Physiological characters turned also out to be species-specific, e.g. daily mycelial growth rates or the temperature range of pure cultures. The production of VOCs can be considered as a very promising tool for fast and reliable species delimitation in the future.

Historical Differentiation and Recent Hybridization in Natural Populations of the Nematode-Trapping Fungus Arthrobotrys oligospora in China

“…At present, we are still far from knowing the full extent of fungal diversity. One major finding based on DNA sequences over the last two decades has been the existence of multiple genetically divergent cryptic species within many previously defined species [ 61 , 62 , 63 , 64 , 65 ]. Within NTF, morphology-based classifications of strains and species have also likely underestimated the true magnitude of species diversity in this group of fungi.…”

Delimiting species in Basidiomycota: a review

“…Species identification in Agaricales has traditionally relied on morphological characters (e.g., Singer 1986;Bas et al 1988;Horak 2005;Knudsen and Vesterholt 2008) that are known to be subject to parallel evolution and phenotypic plasticity (Slepecky and Starmer 2009). In many cases, separation of species based on morphology alone is challenging and many taxa represent complexes with (pseudo)cryptic species (Geml et al 2006;Bickford et al 2007;Carriconde et al 2008;Stefani et al 2014;Balasundaram et al 2015;Guo et al 2016;Sánchez-García et al 2016;Li et al 2017;Peintner et al 2019;Vizzini et al 2019a, b;Nilsen et al 2020;Sato et al 2020;Voitk et al 2020). Putative interspecific hybridization events have been suggested to occur in some Agaricales (Aanen et al 2000;Hughes et al 2013).…”

“…In addition to molecular phylogenetic analyses and morphological study of basidiomata and mycelia, Peintner et al (2019) studied growth characteristics, carried out enzyme assays, and comparatively analyzed volatile compounds in order to resolve cryptic species in Fomes fomentarius s.l. These authors found that the hymenophore pore diameter and the diameter of skeletal hyphae are taxonomically valuable features if measured from statistically relevant structures.…”

Exploring the Species Diversity of Edible Mushrooms in Yunnan, Southwestern China, by DNA Barcoding

“…Thus, having a reliable DNA sequence-based identification for these mushrooms is essential for their correct identification. Indeed, molecular studies have recently shown the existence of many ‘‘cryptic’’ fungal species, which cannot be distinguished morphologically [ 13 , 31 , 32 , 33 ], stressing that molecular information is indispensable for the identification and description of these species and indeed fungal species in general. The internal transcribed spacers (ITSs) of nuclear ribosomal RNA repeat units have frequently been used to identify fungal species.…”