Phylogenetic classification at generic level in the absence of distinct phylogenetic patterns of phenotypical variation: a case study in graphidaceae (ascomycota)

PLoS One. 2012;7(12):e51392. doi: 10.1371/journal.pone.0051392. Epub 2012 Dec 12.

Abstract

Molecular phylogenies often reveal that taxa circumscribed by phenotypical characters are not monophyletic. While re-examination of phenotypical characters often identifies the presence of characters characterizing clades, there is a growing number of studies that fail to identify diagnostic characters, especially in organismal groups lacking complex morphologies. Taxonomists then can either merge the groups or split taxa into smaller entities. Due to the nature of binomial nomenclature, this decision is of special importance at the generic level. Here we propose a new approach to choose among classification alternatives using a combination of morphology-based phylogenetic binning and a multiresponse permutation procedure to test for morphological differences among clades. We illustrate the use of this method in the tribe Thelotremateae focusing on the genus Chapsa, a group of lichenized fungi in which our phylogenetic estimate is in conflict with traditional classification and the morphological and chemical characters do not show a clear phylogenetic pattern. We generated 75 new DNA sequences of mitochondrial SSU rDNA, nuclear LSU rDNA and the protein-coding RPB2. This data set was used to infer phylogenetic estimates using maximum likelihood and Bayesian approaches. The genus Chapsa was found to be polyphyletic, forming four well-supported clades, three of which clustering into one unsupported clade, and the other, supported clade forming two supported subclades. While these clades cannot be readily separated morphologically, the combined binning/multiresponse permutation procedure showed that accepting the four clades as different genera each reflects the phenotypical pattern significantly better than accepting two genera (or five genera if splitting the first clade). Another species within the Thelotremateae, Thelotrema petractoides, a unique taxon with carbonized excipulum resembling Schizotrema, was shown to fall outside Thelotrema. Consequently, the new genera Astrochapsa, Crutarndina, Pseudochapsa, and Pseudotopeliopsis are described here and 39 new combinations are proposed.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Ascomycota / classification*
  • Ascomycota / genetics
  • DNA, Ribosomal / genetics
  • Likelihood Functions
  • Phylogeny*
  • Species Specificity

Substances

  • DNA, Ribosomal

Grants and funding

Funding provided by National Science Foundation (NSF), DEB-1025861 to The Field Museum; PI HTL, CoPI RL, “ATM – Assembling a taxonomic monograph: The lichen family Graphidaceae”. Website: http://www.nsf.gov/awardsearch/showAward.do?AwardNumber=1025861. Collection of material and sequencing work for this study was supported by four NSF grants: TICOLICHEN (DEB-0206125 to The Field Museum; PI RL), Phylogeny and Taxonomy of Ostropalean Fungi, with Emphasis on the Lichen-forming Thelotremataceae (DEB-0516116 to The Field Museum; PI HTL; Co-PI RL), Neotropical Epiphytic Microlichens - An Innovative Inventory of a Highly Diverse yet Little Known Group of Symbiotic Organisms (DEB-0715660 to The Field Museum; PI RL), and ATM - Assembling a taxonomic monograph: The lichen family Graphidaceae (DEB-1025861 to The Field Museum; PI HTL, CoPI RL). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.