A REASSESSMENT OF PHYLOGENETIC SIGNAL IN DNA SEQUENCES FROM THE ITS/5.8S REGION OF THE SYNUROPHYCEAE

Wee 1 , J. L. , Fasone 1,2 , L. D., Sattler 1,3 , A., Starks 1,4 , W. W. & Hurley 5 , D. L. 1 Department of Biological Sciences, Loyola University, New Orleans, LA 70118‐6195, USA; 2 Current address, Department of Biological Sciences, University of New Orleans, New Orleans, LA 70148, USA; 3 Current address, Department of Zoology, Duke University, Durham, NC, 27708‐0325, USA; 4 Current address, University of Tennessee‐Memphis, 255 South Dunlap, Box 108, Memphis, TN, 38126, USA; 5 Department of Cell and Molecular Biology, Tulane University, New Orleans, LA 70118, USA The objective of this study was to enhance the phylogenetic signal contained in the nuclear‐encoded ITS/5.8S region in the Synurophyceae. DNA sequences were determined for internal transcribed spacers 1 and 2, the 5.8S coding region as well as the 18S and 26S flanking regions annealing to PCR primers. DNA sequences were obtained from 15 Synura petersenii strains, 5 additional Synura species, 3 Mallomonas species, Tessellaria volvocina and Chrysodidymus synuroideus. Sequences from the S. petersenii strains and S. uvella aligned unambiguously. A parsimony analysis using S. uvella as the designated outgroup sorted the S. petersenii strains into two well‐supported clades or ITS variants. Sequence variation was low, and sequence divergence values ranged from 0‐1.4% within the ITS variants, to 3%‐4% between the two S. petersenii ITS variants and from 8.5%‐9% between S. uvella and the fifteen S. petersenii isolates. Extensive length variation occurred among the remaining synurophycean sequences (e.g. 495 bp in S. sphagnicola ‐ 598 bp in Tessellaria) and precluded reliable alignments. In the 5.8S coding region, changes at eight positions differed between S. uvella and all of the S. petersenii strains, suggesting that 5.8S sequences should contribute characters with low homoplasy for resolving interspecific relationships in the Synurophyceae. Other workers have used derived RNA transcript secondary structure to facilitate alignments and increase phylogenetic signal in ITS 1 and 2. This presentation summarizes the previous study at the intraspecific level and investigates the interspecific phylogenetic signal in the 5.8S region and in ITS 2 alignments ascertained from secondary structure.