166 Phylogeny of the Chlorophyceae: Inferences from the Chloroplast atpB Gene

Abstract

Phylogenetic reconstruction using the 18S and 26S rDNA genes has proven successful for many chlorophycean lineages, but some nodes remain poorly‐resolved. The chloroplast‐encoded atpB gene has been used to examine phylogenetic problems in several green algal lineages, including the basal streptophytes. However, data for other Chlorophyta are largely unavailable. The class Chlorophyceae, in particular, has not been examined (save for dense sampling among colonial and unicellular flagellates) using the atpB gene. An investigation of variability in the atpB gene for various chlorophycean exemplars was undertaken. Intergeneric distances (p) range from 0.08 (Chlamydomonas reinhardtii vs. Volvox carteri) to 0.24 (Haematococcus lacustris vs. Chloromonas radiata). Distance analysis also reveals high levels of divergence (as compared to the 18S and 26S rDNA data) for the family Sphaeropleaceae. Preliminary phylogenetic reconstructions fail to support a monophyletic Sphaeropleales, but this observation may be due to inadequate taxon sampling. The relative positions of other examplars (e.g., Chaetophora, Elakatothrix, Ascochloris) are largely consistent with interpretations of 18S and 26S rDNA data, although the position of Elakothrix is not robust. These preliminary observations suggest that the atpB gene will provide a powerful complement to current phylogenetic assessments of the Chlorophyceae using 18S and 26S rDNA data. Supported by NSF DEB 9726588 and DEB 0129030.