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  • Digitale Medien  (5)
  • 2005-2009  (5)
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  • Digitale Medien  (5)
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  • 1
    Digitale Medien
    Digitale Medien
    The New Higher Level Classification of Eukaryotes with Emphasis on the Taxonomy of Protists (2005)
    Malden, USA : Blackwell Publishing Inc
    The @journal of eukaryotic microbiology 52 (2005), S. 0 
    Details
    ISSN: 1550-7408
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Abstract. This revision of the classification of unicellular eukaryotes updates that of Levine et al. (1980) for the protozoa and expands it to include other protists. Whereas the previous revision was primarily to incorporate the results of ultrastructural studies, this revision incorporates results from both ultrastructural research since 1980 and molecular phylogenetic studies. We propose a scheme that is based on nameless ranked systematics. The vocabulary of the taxonomy is updated, particularly to clarify the naming of groups that have been repositioned. We recognize six clusters of eukaryotes that may represent the basic groupings similar to traditional “kingdoms.” The multicellular lineages emerged from within monophyletic protist lineages: animals and fungi from Opisthokonta, plants from Archaeplastida, and brown algae from Stramenopiles.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1550-7408.2005.00053.x
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  • 2
    Digitale Medien
    Digitale Medien
    Saccamminid foraminifers from anoxic sediments: implications for Proterozoic ecosystem dynamics (2005)
    Oxford, UK : Blackwell Science Inc
    The @journal of eukaryotic microbiology 52 (2005), S. 0 
    Details
    ISSN: 1550-7408
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Eukaryote origin and earliest diversification occurred in the Proterozoic when Earth's atmosphere was undoubtedly different from that of today. Atmospheric oxygen levels were increasing from the primordial anoxic atmosphere due, for example, to cyanobacterial oxygenic photosynthesis. Late Proterozoic (∼0.6–0.9 Gya) deep-ocean oxygen concentrations are less certain, but geochemical evidence suggests anoxia and hydrogen-sulfide enrichment. It can, therefore, be postulated that initial eukaryotic diversification occurred in oxygen-depleted, sulfide-enriched environments. Foraminifera are aerobes and, thus, not expected in anoxic settings. Recently, however, we found a saccamminid allogromian in a deep-water anoxic, sulfidic setting. Samples were collected from Santa Barbara Basin (California) when bottom-water oxygen was undetectable and sediments smelled strongly of hydrogen sulfide. Foraminiferal SSU rDNA sequences recovered from sediments included one from a previously uncharacterized saccamminid. Ultrastructural analysis indicated the presence of intact Golgi, mitochondria, and prokaryotic endobionts. Saccamminid occurrence in environmental conditions known to exist during the Proterozoic supports the possibility of their origin early in eukaryotic evolution. Extant saccamminids could have competed well in the prokaryote-dominated Proterozoic benthic ecosystem given their diet includes bacteria, bacterial biofilms and unicellular algae. Thus, Proterozoic foraminifers may have been top carnivores.Funded by NASA NRA-01-01-EXB-057, the Geological Society of America's W. Storrs Cole Memorial Research Award, and NSF OPP0003639.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1550-7408.2005.05202003_1_12.x
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  • 3
    Digitale Medien
    Digitale Medien
    The shell or the kernel: biodiversity estimates of benthic foraminifera (2005)
    Oxford, UK : Blackwell Science Inc
    The @journal of eukaryotic microbiology 52 (2005), S. 0 
    Details
    ISSN: 1550-7408
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Estimates of protist biodiversity and distribution have until recently relied on the morphological identification of individual cells. The advent of environmental-DNA-based surveys of these protist communities has broadened our understanding of species richness and diversity. A “total-evidence biodiversity” approach gives two benefits. First, it allows “back-comparison” to previous studies of ecosystems, permitting estimates of the amount of cryptic diversity in different sampling regimes (and by extension, the fossil record). Second, it will provide the best possible estimate of the total species richness of current study sites. Here, we use a well-studied benthic protist community, the foraminiferal assemblage of McMurdo Sound, Antarctica, to determine the effective parameters of both detection methods. We find that molecular-based techniques detect well-characterized calcareous species at depths too great to allow calcification, suggesting that these forms may be able to survive without their distinctive tests. “Fragile” taxa also appear to be better represented in molecular surveys than in morphological ones. The strengths of a combined morphological–molecular approach are demonstrated by an assessment of the distribution of two species in the genus Notodendrodes; morphological detection excels in the identification of distinctive, patchily distributed adults, whereas molecular detection with taxon-specific probes enabled identification in less favorable sampling conditions. Such a “broad-plus-deep” approach appears to maximize detection efficiency in this Antarctic setting.Work supported by NSF OPP0003639.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1550-7408.2005.05202003_1_31.x
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  • 4
    Digitale Medien
    Digitale Medien
    Divergent β-tubulins from foraminifera: Implications for microtubule assembly (2005)
    Oxford, UK : Blackwell Science Inc
    The @journal of eukaryotic microbiology 52 (2005), S. 0 
    Details
    ISSN: 1550-7408
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Foraminifera utilize an unusual and very rapid microtubule assembly/disassembly system: a state transition between microtubules and helical filaments. The helical filament is an assembly polymorph that forms when the microtubule lattice uncoils into a ribbon of tubulin dimers connected only by lateral subunit/subunit bonds. An unusual β-tubulin sequence, which may be implicated in this process, has previously been reported from the foraminiferan Reticulomyxa filosa. In order to determine the taxonomic distribution and possible significance of this tubulin isoform, we sequenced and analyzed β-tubulin genes from a broad taxonomic range of foraminifera. These genes contain a large number of substitutions, conserved within the group, which may alter the biochemical properties of β-tubulin, especially in regions involved in subunit/subunit binding between α- and β-tubulin in the microtubule lattice. In particular, the M-loop, which is intimately involved in lateral subunit binding, shows only 30% homology to the consensus sequence for eukaryotic β-tubulins. Multiple regions identified to be involved in longitudinal contacts with α-tubulin are also highly substituted. In contrast, the foraminiferal α-tubulin is well conserved with its homologs in other organisms. We suggest that these alterations to the consensus eukaryotic β-tubulin sequence may help to explain the unusual assembly properties of foraminiferal microtubules.This work was supported by NSF OPP0003639.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1550-7408.2005.05202003_1_82.x
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  • 5
    Digitale Medien
    Digitale Medien
    Foraminiferal evolution as revealed by β-tubulin data (2005)
    Oxford, UK : Blackwell Science Inc
    The @journal of eukaryotic microbiology 52 (2005), S. 0 
    Details
    ISSN: 1550-7408
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Foraminiferal taxonomy is traditionally based on morphological characteristics, particularly the structure and composition of the test (shell). Recently, a comprehensive SSU-based molecular phylogeny confirmed some multi-chambered foraminiferal groups while enhancing our understanding of the single-chambered, or the so-called “allogromiid”, taxa. However, some relationships, such as the origin of the foraminiferal order Miliolida, remain unresolved, suggesting an approach involving multiple data sources may improve understanding. Here, we discuss the evolutionary implications of β-tubulin genes from several species of foraminifera. Foraminiferal β-tubulin is highly divergent, possibly indicating a period of accelerated evolution of this gene at the base of the foraminiferal lineage, but it is well-conserved within the group. We show its utility in helping to resolve the phylogenetic position of Miliammina fusca, a foraminiferan whose proper classification has been debated for 70 years. M. fusca is a morphological “chimera”, and we show that its placement in SSU trees is not particularly robust. However, β-tubulin data assigns Miliammina to the Miliolida, some of whose members show a similar chamber coiling pattern. This placement agrees with an earlier observation that M. fusca's actin isoforms more closely resemble those of traditional milolids. This finding implies that test formation can revert from calcareous to agglutinated, suggesting a reexamination of some relationships inferred from the fossil record.Supported by NSF OPP0003639.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1550-7408.2005.05202003_1_32.x
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