PHYLOGENY OF THE GENUS CHLOROCOCCUM: A STUDY OF 18S AND 26S rRNA GENE SEQUENCES

• Published in: Journal of phycology Vol. 36; no. s3; p. 47
• Main Authors: Michalopulos, J.U., Buchheim, J.A., Buchheim
• Format: Journal Article
• Language: English
• Published: Boston, MA, USA Blackwell Science Inc 01.12.2000
• Subjects: Chlamydomonadales; Chlorococcum; Chlorophyta; Freshwater
• ISSN: 0022-3646; 1529-8817
• DOI: 10.1046/j.1529-8817.1999.00001-140.x

Phylogenetic studies of 18S rRNA gene sequence data support an alliance of the green algal genus, Chlorococcum, with other chlamydomonadalean taxa that produce walled, motile stages. Moreover, these phylogenetic studies indicate that Chlorococcum is not monophyletic, but rather falls into two distinct lineages. However, these molecular phylogenetic studies were based on only a few taxa in a genus that exhibits marked habitat diversity. In particular, numerous species of Chlorococcum currently in the UTEX collection have been isolated from naturally acidic environments. Except for a few groups (e.g., desmids), acidic environments are not generally regarded as niches for widespread exploitation by green algae. A new investigation of diversity among species of Chlorococcum included broader taxon and data sampling schemes. Sequence data from both the nuclear‐encoded 18S and 26S rRNA genes were collected from 17 different UTEX and SAG isolates of Chlorococcum. In addition, controlled growth experiments at varying acidity (pH 5.0, 6.0, and 8.0) were conducted. Results of these investigations suggest that the Chlorococcum‐like morphology has evolved in at least three lineages. Furthermore, these data suggest that the ability to grow optimally at low pH has independently evolved in several lineages.