Abstract
The distribution of microbial species, including fungi, has long been considered cosmopolitan. Recently, this perception has been challenged by molecular studies in historical biogeography, phylogeny and population genetics. Here we explore this issue using the fungal morphological species Thelonectria discophora, one of the most common species of fungi in the family Nectriaceae, encountered in almost all geographic regions and considered as a cosmopolitan taxon. In order to determine if T. discophora is a single cosmopolitan species or an assemblage of sibling species, we conducted various phylogenetic analyses, including standard gene concatenation, Bayesian concordance methods, and coalescent-based species tree reconstruction on isolates collected from a wide geographic range. Results show that diversity among isolates referred as T. discophora is greatly underestimated and that it represents a species complex. Within this complex, sixteen distinct highly supported lineages were recovered, each of which has a restricted geographic distribution and ecology. The taxonomic status of isolates regarded as T. discophora is reconsidered, and the assumed cosmopolitan distribution of this species is rejected. We discuss how assumptions about geographically widespread species have implications regarding their taxonomy, true diversity, biological diversity conservation, and ecological functions.
Highlights
The high plasticity of morphological characters in fungi led early taxonomists to group or ‘‘lump’’ similar-looking species into one individual species
The rpb1 region showed the highest sequence variability and number of parsimony informative sites, while the ribosomal genes (ITS, LSU) exhibited low levels of variation, approximately more than half that observed in rpb1 (Table S2)
Bayesian and Maximum Likelihood Analyses By combining the evidence found in the concatenated phylogenetic analyses, a total of sixteen putative species were recovered, having significant Maximum likelihood (ML) bootstrap (.70%) and Bayesian Inference analysis (BI) posterior probability (.0.95) support (Figure 2)
Summary
The high plasticity of morphological characters in fungi led early taxonomists to group or ‘‘lump’’ similar-looking species into one individual species As this species was found in a wide geographic range, it was labeled as being cosmopolitan i.e., having a worldwide distribution. This resulted in long-held assumptions about long-distance dispersal capabilities in fungi [1,2], a trend that was assumed for other microorganisms such as protozoa, protophytes, and other small organisms (i.e., those less than 1 mm in length such as nematodes, rotifers and marine invertebrates) [3,4,5,6,7]. Studies have found that there is a distinctive correlation between geographical distance and similarity in community composition (distance-decay relationship) observed in local to global-scale analyses [9]
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