Abstract
BackgroundPhylogenetic studies, particularly those based on rDNA sequences from plant roots and basidiomata, have revealed a strikingly high genetic diversity in the Sebacinales. However, the factors determining this genetic diversity at higher and lower taxonomic levels within this order are still unknown. In this study, we analysed patterns of genetic variation within two morphological species, Sebacina epigaea and S. incrustans, based on 340 DNA haplotype sequences of independent genetic markers from the nuclear (ITS + 5.8S + D1/D2, RPB2) and mitochondrial (ATP6) genomes for 98 population samples. By characterising the genetic population structure within these species, we provide insights into species boundaries and the possible factors responsible for genetic diversity at a regional geographic scale.ResultsWe found that recombination events are relatively common between natural populations within Sebacina epigaea and S. incrustans, and play a significant role in generating intraspecific genetic diversity. Furthermore, we also found that RPB2 and ATP6 genes display higher levels of intraspecific synonymous polymorphism. Phylogenetic and demographic analyses based on nuclear and mitochondrial loci revealed three distinct phylogenetic lineages within of each of the morphospecies S. epigaea and S. incrustans: one major and widely distributed lineage, and two geographically restricted lineages, respectively. We found almost no differential morphological or ecological characteristics that could be used to discriminate between these lineages.ConclusionsOur results suggest that recombination and negative selection have played significant roles in generating genetic diversity within these morphological species at small geographical scales. Concordance between gene genealogies identified lineages/cryptic species that have evolved independently for a relatively long period of time. These putative species were not associated with geographic provenance, geographic barrier, host preference or distinct phenotypic innovations.
Highlights
Phylogenetic studies, those based on rDNA sequences from plant roots and basidiomata, have revealed a strikingly high genetic diversity in the Sebacinales
Phylogenetic analysis of our own complete ITS sequences and those of Sebacina basidiomata available from the GenBank/UNITE databases placed some of our sequences in rather isolated positions (Figure 2), except for S. epigaea haplotype H3 was identical to UDB016431 and haplotype H4 was identical to UDB016419 both from Estonia, respectively
For S. incrustans, haplotypes H2, H3 and H4 appeared to be identical to EF644113 (Austria), UDB000118 (Denmark) and AY143340 (Germany); haplotype H5 the same as UDB000774 (Denmark); and haplotype H8 to be identical to AJ966751, AJ966752 and AJ966753
Summary
Phylogenetic studies, those based on rDNA sequences from plant roots and basidiomata, have revealed a strikingly high genetic diversity in the Sebacinales. Molecular markers are very helpful for this purpose, especially within fungus groups with comparatively simple body plans that seriously restrict the number of constant and recognisable characters This is the case in the Sebacinales, where high genetic diversity has been reported from the analysis of rDNA sequences of lineages with low levels of morphological variation, see e.g. Sebacina epigaea and S. incrustans are both broadly distributed in Europe and form mycorrhizal associations with forest trees [14] and/or orchids [15] Both species are relatively easy to recognise and distinguish from one another in the field providing an exceptional opportunity to study their intraspecific diversity in combination with an evaluation of their ecological and morphological characteristics
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