ITS, OTUs and beyond—fungal hyperdiversity calls for supplementary solutions

Abstract

Molecular species recognition of fungi emerged years before DNA barcoding (Seifert 2009). While the ideal fungal DNA barcode seems Utopian, two research decades nevertheless highlight the internal transcribed spacer (ITS) as the best available choice (Seifert 2009). Databases providing reliable ITS sequences of known fungi require enormous efforts, but are urgently needed (Abarenkov et al. 2010a,b; Begerow et al. 2010). Any criticism of such a commitment seems unjustified. However, exclusive focus on the development of ITS reference libraries will delay the progress towards a deeper ecological insight. It is widely acknowledged that ITS fails to recognize species, particularly in some ascomycete lineages (Balajee et al. 2009; Seifert 2009). It also appears paradoxical to solely rely on ITS for ecological recognition of fungal species when modern fungal systematics rely on phylogenetic species recognition with concordance of multiple gene genealogies (see Blackwell 2011). Considering that at least 98% of the predicted ∼5 million fungal species remain undescribed (Blackwell 2011), how will reliance on ITS alone influence the biodiversity estimates and ecological understanding? In this issue, Gazis et al. (2011) elegantly demonstrate through multi-locus sequence phylogeny analyses that ITS largely underestimates the species diversity of tropical fungal endophytes and even more importantly obscures fundamental ecological and biogeographical patterns. This thorough reflection on species delimitation criteria and their implications for ecological and biogeographical inferences underline that ITS, particularly in hyperdiverse habitats, provides no shortcut to deeper knowledge of fungal ecology.