Phylogeny of the VLE-14 Chlamydomonas (Chlorophyceae) group: A study of 18S rRNA gene sequences

Comparative specificity of sporangial wall autolysins (i.e. vegetative lytic enzymes [VLE]) derived from sporulating cultures has been wed to group Chlamydomonas taxa into 15 different VLE types. The VLE-14 group including isolates of C. geitleri, C. noctigama, C. monoica, C. pinicola, C. terricola, and C. hindakii, is one of the largest of these VLE groups. Genetic studies have shown that a number of the VLE-14 taxa are interfertile, albeit with little or reduced viability of progeny. A reevaluation of the VLE-14 group suggested that all members should be regarded as distinct isolates of C. noctigama. The present investigation tests the phylogenetic implications of the VLE evidence and examines the validity of the taxonomic reevaluation in a phylogenetic context by analysis of 18S rRNA gene sequence data. Results from analyses of the sequence data are consistent with an interpretation of the VLE evidence as indicative of monophyletic taxa. Phylogenetic analyses of the sequence data are also consistent with the taxonomic reevaluation and reidentification of the group. However, at least some of the VLE-14 isolates studied in this investigation fit criteria for distinct biologic or phylogenetic species. It is concluded that the VLE-14 taxa represent a very closely allied group that includes some isolates that are in the early stages of speciation by reproductive isolation.