Regular Article
Ribosomal DNA and Resolution of Branching Order among the Ascomycota: How Many Nucleotides Are Enough?

https://doi.org/10.1006/mpev.2000.0835Get rights and content

Abstract

Molecular phylogenies for the fungi in the Ascomycota rely heavily on 18S rRNA gene sequences but this gene alone does not answer all questions about relationships. Particularly problematical are the relationships among the first ascomycetes to diverge, the Archiascomycetes, and the branching order among the basal filamentous ascomycetes, the Euascomycetes. Would more data resolve branching order? We used the jackknife and bootstrapping resampling approach that constitutes the “pattern of resolved nodes” method to address the relationship between number of variable sites in a DNA sequence alignment and support for taxonomic clusters. We graphed the effect of increasing sizes of subsamples of the 18S rRNA gene sequences on bootstrap support for nodes in the Ascomycota tree. Nodes responded differently to increasing data. Some nodes, those uniting the filamentous ascomycetes for example, would still have been well supported with only two thirds of the 18S rRNA gene. Other nodes, like the one uniting the Archiascomycetes as a monophyletic group, would require about double the number of variable sites available in the 18S gene for 95% neighbor-joining bootstrap support. Of the several groups emerging at the base of the filamentous ascomycetes, the Pezizales receive the most support as the first to diverge. Our analysis suggests that we would also need almost three times as much sequence data as that provided by the 18S gene to confirm the basal position for the Pezizales and more than seven times as much data to resolve the next group to diverge. If more data from other genes show the same pattern, the lack of resolution for the filamentous ascomycetes may indicate rapid radiation within this clade.

References (22)

There are more references available in the full text version of this article.

Cited by (60)

  • The genus Bipolaris

    2014, Studies in Mycology
    Citation Excerpt :

    Later authors did not accept this approach and claimed that generic differences are evident (Talbot 1973, Luttrell 1977, 1978). Molecular phylogenetic analysis based on ITS (internal transcribed spacers and intervening 5.8S nrDNA) and GPDH (partial glyceraldehyde-3-phosphate dehydrogenase) genes (Berbee et al. 2000) showed Drechslera and Bipolaris to be two distinct genera. Bipolaris and Curvularia Boedijn (1933) share many morphological similarities, and both genera have sexual morphs in Cochliobolus.

  • Phylogenetic relationships of coprophilous Pleosporales (Dothideomycetes, Ascomycota), and the classification of some bitunicate taxa of unknown position

    2006, Mycological Research
    Citation Excerpt :

    Taxa were sampled to ensure that representatives of the major orders within the Dothideomycetes and taxa of the major families within Pleosporales were included in the study. The backbone of the tree of the higher ascomycetes is uncertain (Berbee et al. 2000; Tehler et al. 2003; Lutzoni et al. 2004; Lumbsch et al. 2005), and therefore, we also included representatives of the major classes Arthoniomycetes, Eurotiomycetes (including Chaetothyriomycetes), Lecanoromycetes, and Sordariomycetes. Hypocrea lutea and Xylaria hypoxylon, representing the Sordariomycetes, were chosen as out-groups.

View all citing articles on Scopus
1

To whom correspondence should be addressed. Fax: (604) 822-6089. E-mail: [email protected].

View full text