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Orr R.J.S.,University of Oslo | Murray S.A.,University of New South Wales | Murray S.A.,Sydney Institute of Marine Science | Stuken A.,University of Oslo | And 2 more authors.
PLoS ONE | Year: 2012

The dinoflagellates are a diverse lineage of microbial eukaryotes. Dinoflagellate monophyly and their position within the group Alveolata are well established. However, phylogenetic relationships between dinoflagellate orders remain unresolved. To date, only a limited number of dinoflagellate studies have used a broad taxon sample with more than two concatenated markers. This lack of resolution makes it difficult to determine the evolution of major phenotypic characters such as morphological features or toxin production e.g. saxitoxin. Here we present an improved dinoflagellate phylogeny, based on eight genes, with the broadest taxon sampling to date. Fifty-five sequences for eight phylogenetic markers from nuclear and mitochondrial regions were amplified from 13 species, four orders, and concatenated phylogenetic inferences were conducted with orthologous sequences. Phylogenetic resolution is increased with addition of support for the deepest branches, though can be improved yet further. We show for the first time that the characteristic dinoflagellate thecal plates, cellulosic material that is present within the sub-cuticular alveoli, appears to have had a single origin. In addition, the monophyly of most dinoflagellate orders is confirmed: the Dinophysiales, the Gonyaulacales, the Prorocentrales, the Suessiales, and the Syndiniales. Our improved phylogeny, along with results of PCR to detect the sxtA gene in various lineages, allows us to suggest that this gene was probably acquired separately in Gymnodinium and the common ancestor of Alexandrium and Pyrodinium and subsequently lost in some descendent species of Alexandrium. © 2012 Orr et al. Source

Orr R.J.S.,University of Oslo | Stuken A.,University of Oslo | Murray S.A.,University of New South Wales | Murray S.A.,Sydney Institute of Marine Science | Jakobsen K.S.,University of Oslo
Applied and Environmental Microbiology | Year: 2013

Saxitoxin and its derivatives are potent neurotoxins produced by several cyanobacteria and dinoflagellate species. SxtA is the initial enzyme in the biosynthesis of saxitoxin. The dinoflagellate full mRNA and partial genomic sequences have previously been characterized, and it appears that sxtA originated in dinoflagellates through a horizontal gene transfer from a bacterium. So far, little is known about the remaining genes involved in this pathway in dinoflagellates. Here we characterize sxtG, an amidinotransferase enzyme gene that putatively encodes the second step in saxitoxin biosynthesis. In this study, the entire sxtG transcripts from Alexandrium fundyense CCMP1719 and Alexandrium minutum CCMP113 were amplified and sequenced. The transcripts contained typical dinoflagellate spliced leader sequences and eukaryotic poly(A) tails. In addition, partial sxtG transcript fragments were amplified from four additional Alexandrium species and Gymnodinium catenatum. The phylogenetic inference of dinoflagellate sxtG, congruent with sxtA, revealed a bacterial origin. However, it is not known if sxtG was acquired independently of sxtA. Amplification and sequencing of the corresponding genomic sxtG region revealed noncanonical introns. These introns show a high interspecies and low intraspecies variance, suggesting multiple independent acquisitions and losses. Unlike sxtA, sxtG was also amplified from Alexandrium species not known to synthesize saxitoxin. However, amplification was not observed for 22 non-saxitoxin-producing dinoflagellate species other than those of the genus Alexandrium or G. catenatum. This result strengthens our hypothesis that saxitoxin synthesis has been secondarily lost in conjunction with sxtA for some descendant species. © 2013, American Society for Microbiology. Source

Thessen A.E.,Center for Library and Informatics | Patterson D.J.,Center for Library and Informatics | Murray S.A.,University of New South Wales | Murray S.A.,Sydney Institute of Marine Science
PLoS ONE | Year: 2012

Taxonomists have been tasked with cataloguing and quantifying the Earth's biodiversity. Their progress is measured in code-compliant species descriptions that include text, images, type material and molecular sequences. It is from this material that other researchers are to identify individuals of the same species in future observations. It has been estimated that 13% to 22% (depending on taxonomic group) of described species have only ever been observed once. Species that have only been observed at the time and place of their original description are referred to as oncers. Oncers are important to our current understanding of biodiversity. They may be validly described species that are members of a rare biosphere, or they may indicate endemism, or that these species are limited to very constrained niches. Alternatively, they may reflect that taxonomic practices are too poor to allow the organism to be re-identified or that the descriptions are unknown to other researchers. If the latter are true, our current tally of species will not be an accurate indication of what we know. In order to investigate this phenomenon and its potential causes, we examined the microbial eukaryote genus Gymnodinium. This genus contains 268 extant species, 103 (38%) of which have not been observed since their original description. We report traits of the original descriptions and interpret them in respect to the status of the species. We conclude that the majority of oncers were poorly described and their identity is ambiguous. As a result, we argue that the genus Gymnodinium contains only 234 identifiable species. Species that have been observed multiple times tend to have longer descriptions, written in English. The styles of individual authors have a major effect, with a few authors describing a disproportionate number of oncers. The information about the taxonomy of Gymnodinium that is available via the internet is incomplete, and reliance on it will not give access to all necessary knowledge. Six new names are presented - Gymnodinium campbelli for the homonymous name Gymnodinium translucens Campbell 1973, Gymnodinium antarcticum for the homonymous name Gymnodinium frigidum Balech 1965, Gymnodinium manchuriensis for the homonymous name Gymnodinium autumnale Skvortzov 1968, Gymnodinium christenum for the homonymous name Gymnodinium irregulare Christen 1959, Gymnodinium conkufferi for the homonymous name Gymnodinium irregulare Conrad & Kufferath 1954 and Gymnodinium chinensis for the homonymous name Gymnodinium frigidum Skvortzov 1968. © 2012 Thessen et al. Source

Mullaney T.J.,University of New South Wales | Suthers I.M.,University of New South Wales | Suthers I.M.,Sydney Institute of Marine Science
Limnology and Oceanography | Year: 2013

We examined the fate of larval fish assemblages after the East Australian Current (EAC) had separated from the coast and larval fish were advected eastward along the Tasman Front. There was no difference in the assemblages at four stations as the EAC meandered from the continental shelf to 220 km eastward. At a fifth station, we sampled a submesoscale, frontal eddy that had formed at the EAC separation zone 11 d earlier and had entrained shelf water. Zooplankton biomass was greater within the eddy compared to the adjacent shelf. The larval fish assemblage in the eddy was significantly different from all other stations. There was an order of magnitude greater abundance of three species characteristic of the shelf: sardine (Sardinops sagax; Clupeidae), blue mackerel (Scomber australasicus; Scombridae), and yellowtail scad (Trachurus novaezelandiae; Carangidae), which were also significantly larger than larvae from a station on the adjacent shelf. In particular, S. sagax in the eddy were,~5 mm longer and,~10 d older, although growth rates were similar. Larval retention in the eddy was inferred from the co-occurrence of small and large larvae of all three species compared to the adjacent shelf. The EAC is only 20-30 km from the inner-shelf water, where frontal eddies may facilitate three stages of successful recruitment: entrainment, enrichment, and retention. Frontal eddies off southeastern Australia entrain preconditioned shelf water, move slower than the mean flow of the EAC, decreasing transport rates, and may sustain planktonic communities through eddy uplift. These eddies are frequent and short-lived (2 to 4 weeks), and we suspect they are of fisheries importance as their duration is sufficient for fish larvae to complete their early life history and, presumably, recruit back to the coast. © 2013, by the Association for the Sciences of Limnology and Oceanography, Inc. Source

Burke C.,University of New South Wales | Thomas T.,University of New South Wales | Lewis M.,J. Craig Venter Institute | Steinberg P.,University of New South Wales | And 3 more authors.
ISME Journal | Year: 2011

Green Ulvacean marine macroalgae are distributed worldwide in coastal tidal and subtidal ecosystems. As for many living surfaces in the marine environment, little is known concerning the epiphytic bacterial biofilm communities that inhabit algal surfaces. This study reports on the largest published libraries of near full-length 16S rRNA genes from a marine algal surface (5293 sequences from six samples) allowing for an in-depth assessment of the diversity and phylogenetic profile of the bacterial community on a green Ulvacean alga. Large 16S rRNA gene libraries of surrounding seawater were also used to determine the uniqueness of this bacterial community. The surface of Ulva australis is dominated by sequences of Alphaproteobacteria and the Bacteroidetes, especially within the Rhodobacteriaceae, Sphingomonadaceae, Flavobacteriaceae and Sapropiraceae families. Seawater libraries were also dominated by Alphaproteobacteria and Bacteroidetes sequences, but were shown to be clearly distinct from U. australis libraries through the clustering of sequences into operational taxonomic units and Bray-Curtis similarity analysis. Almost no similarity was observed between these two environments at the species level, and only minor similarity was observed at levels of sequence clustering representing clades of bacteria within family and genus taxonomic groups. Variability between libraries of U. australis was relatively high, and a consistent sub-population of bacterial species was not detected. The competitive lottery model, originally derived to explain diversity in coral reef fishes, may explain the pattern of colonization of this algal surface. © 2011 International Society for Microbial Ecology All rights reserved. Source

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