Fabbro LD, Duivenvoorden LJ

A two-part model linking multidimensional environmental gradients and seasonal succession of phytoplankton assemblages
HYDROBIOLOGIA 438 (1-3): 13-24 NOV 2000

Abstract:
Algal assemblages and their respective niches are analysed for a large riverine impoundment in semi-arid Australia. The extreme variability of the flow regime and the extensive period of low or no flow produced conditions including prolonged stratification akin to those of a lake during the dry season. Hierarchical agglomerative clustering of phytoplankton data and comparison with a principal component analysis of corresponding environmental data are used to demonstrate the linkage between steep environmental gradients and variations in the phytoplankton assemblages. The factor score plots separate the algal assemblages according to key environmental parameters including increasing clarity of the water column, temperature and modification of water chemistry. Assemblages normally contained cyanoprokaryotes (Oscillatoriales), euglenophytes or non-flagellated chlorophytes during flows followed by flagellated chlorophytes and cyanoprokaryotes (Nostocales) during the dry season. Species present during the period of reduced flow occupied conditions similar to those presented in the literature for temperate and/or tropical lakes. Common species included Pandorina morum, Eudorina elegans, Anabaena circinalis, Aphanizomenon issatschenkoi, Aphanizomenon aphanizomenioides and Cylindrospermopsis raciborskii. A two-part model is proposed which predicts the most likely genera of phytoplankton with respect to multidimensional environmental gradients.

Nozaki H, Misawa K, Kajita T, et al.

Origin and evolution of the colonial Volvocales (Chlorophyceae) as inferred from multiple, chloroplast gene sequences
MOL PHYLOGENET EVOL 17 (2): 256-268 NOV 2000

Abstract:
A combined data set of DNA sequences (6021 bp) from five protein-coding genes of the chloroplast genome (rbcL, atpB, psaA, psaB, and psbC genes) were analyzed for 42 strains representing 30 species of the colonial Volvocales (Volvox and its relatives) and 5 related species of green algae to deduce robust phylogenetic relationships within the colonial green flagellates. The 4-celled family Tetrabaenaceae was robustly resolved as the most basal group within the colonial Volvocales. The sequence data also suggested that all five volvocacean genera with 32 or more cells in a vegetative colony (all four of the anisogamous/oogamous genera, Eudorina, Platydorina, Pleodorina, and Volvox, plus the isogamous genus Yamagishiella) constituted a large monophyletic group, in which 2 Pleodorina species were positioned distally to 3 species of Volvox. Therefore, most of the evolution of the colonial Volvocales appears to constitute a gradual progression in colonial complexity and in types of sexual reproduction, as in the traditional volvocine lineage hypothesis, although reverse evolution must be considered for the origin of certain species of Pleodorina. Data presented here also provide robust support for a monophyletic family Goniaceae consisting of two genera: Gonium and Astrephomene. (C) 2000 Academic Press.