PHYLOGENETIC ANALYSIS OF 32 STRAINS OFVAUCHERIA(XANTHOPHYCEAE) USING THErbcL GENE AND ITS TWO FLANKING SPACER REGIONS1

Abstract

The completerbcL gene was sequenced for 21 species and 32 strains ofVaucheriaand for five other Xanthophyceae (Asterosiphon dichotomus(Kützing) Rieth,Botrydium becharianumVischer,B. cystosumVischer,B. stoloniferumMitra,Tribonema intermixtumPascher). ThepsbA‐rbcL spacer, upstream of therbcL gene, and the RUBISCO spacer between therbcL andrbcS genes were also completely sequenced for theVaucheriastrains andAsterosiphon.ThepsbA‐rbcL spacer was the most variable region that was sequenced, and only the 3′ end of the spacer could be aligned. Phylogenetic analyses (maximum parsimony, neighbor joining, and maximum likelihood) were conducted using the DNA sequence and the amino acid sequence for therbcL gene, and a second analysis was conducted using a portion of thepsbA‐rbcL spacer +rbcL gene + RUBISCO spacer. All analyses showed thatVaucheriaspecies formed monophyletic clades that corresponded with morphologically based subgeneric sections, including the section Racemosae. Species producing a gametophore (= fruiting branch, bearing both an antheridium and oogonium) formed a monophyletic clade in all analyses. The nongametophore species sometimes formed a monophyletic clade but other times formed a basal grade. Pair‐wise comparisons of nucleotides and amino acids showed that for some species, numerous nucleotide changes resulted in relatively few amino acid changes. Consequently, phylogenetic analysis of the amino acids produced numerous trees, which in a strict consensus tree resulted in numerous polychotomies. An original strain ofV. terrestristhat was deposited in two culture collections over 25 years ago had identical sequences, suggesting no rapid change was occurring in the sequenced regions. Two strains ofV. prona, isolated from Europe and North America, had identical sequences. Other species, for which two or more strains were examined, had different sequences. These results suggest that cryptic species complexes exist withinVaucheriabecause therbcL gene is a conservative gene that is identical in other protists.