CONCORDANCE OF MOLECULAR AND ULTRASTRUCTURAL DATA IN THE STUDY OF ZOOSPORIC CHLOROCOCCALEAN GREEN ALGAE¹

Abstract

Alternative evolutionary hypotheses generated from features of vegetative cell morphology and motile cell ultra‐structure were investigated using a molecular data set. Complete nuclear‐encoded small subunit (18S) ribosomal RNA (rRNA) gene sequences were determined for six species (three each) of the chlorococcalean green algae “Neo chloris” and Characium. Based on motile cell ultra‐structure, it was previously shown that both genera could be separated into three distinct groups possibly representing three separate orders and two classes of green algae. 18S rRNA gene sequences were also obtained for three additional taxa, Dunaliella parva Lerche, Pediastrum duplex Meyen, and Friedmannia israelensis Chantanachat and Bold. These organisms were selected because each, in turn, is a representative of one of the three ultrastructural groups into which the Neochloris and Characium species are separable. Phylogenetic analyses utilizing the molecular data fully support the ultrastructural findings, suggesting that the similar vegetative cell morphologies observed in these organisms have resulted from convergence.

Phylogeography of microbial phototrophs in the dry valleys of the high Himalayas and Antarctica

“…Given the known distribution of M. vaginatus in the world's major deserts, it is reasonable to assume that its dormant dust-borne propagules are being constantly deposited in areas where they may not be able to function. By contrast, the CP clade is not a known desert dweller [45,46], nor are any dormant structures known for the few studied species in this clade [32,45].…”

“…Perhaps even more significantly, the CP clade contains the only algal sequence so far amplified and cloned from cryoconite-hole sediments of the McMurdo Dry Valleys [30]. This strongly supported monophyletic clade [31,32] also encompasses a terrestrial 'snow' alga isolated from the high (798 N) Arctic [33] and a dominant group of algae detected in clone libraries of barren soils from near the continental divide in Colorado, USA ([14]; figure 2). Taken together, these findings are the first molecular evidence of a globally dispersed, cryophillic clade of terrestrial algae and provide a unique opportunity to test whether extreme cryophiles are genetically the same across these geographically very distant sites.…”

“…To perform such a test on the CP clade, we analysed pairwise comparisons of genetic distance versus The CP clade (Chlamydopodium -Pleurastrum) was strongly supported by both methods and has been shown to be a monophyletic clade in previous research [31,32,34], although this is the first study to show their widespread distribution in cold-soil environments. Antarctic phylotypes without accession numbers are environmental sequences from Antarctic Dry Valley soils [8], and all branches labelled 'Colorado' are from soils near the Arikaree Glacier and the continental divide [14].…”

Phylogeny and Molecular Evolution of the Green Algae

“…For example, strains conforming to the morphological circumscription of the genera Neochloris, Characium and Planophila have been found in all three classes (Watanabe & Floyd, 1989;Lewis et al, 1992;Watanabe et al, 2000;Friedl & O'Kelly, 2002). Similarly, species of the coccoid genus Chlorococcum and the filamentous genus Uronema were present in the Chlorophyceae as well as the Ulvophyceae (Watanabe et al, 2001;Krienitz et al, 2003;Leliaert et al, 2009a).…”

The evolution of the diatoms (Bacillariophyta). I. Origin of the group and assessment of the monophyly of its major divisions

“…when pairwise combinations are made at the class or order level (0"08 to 0.04, respectively; Lewis et al, 1992), between closely related families , and between genera of the same family (Schlegel et al, 1991) in these algal and protozoan studies. However, in the Rhodophyta (Bird et al, 1992) and the Phaeophyta (Saunders & Druehl, 1992), distance values at comparable taxonomic levels are disparate, indicating that molecular and morphological (taxonomic) divergency times are not congruent in these groups.…”