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  • 1
    Electronic Resource
    Electronic Resource
    Comparison of Ribosomal and Isozymic Phylogenies of Tetrahymenine Ciliates (1989)
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 36 (1989), S. 0 
    Details
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A recent analysis of sequence variations in ribosomal RNA's from 31 species of tetrahymenine ciliates groups them into 9 sets referred to as “ribosets.” These species associations are not well correlated with the distributions of distinctive morphological characteristics. The phylogenetic structure suggests that modem “pyriform” tetrahymenines may be paraphyletic survivors of primitive design and that the morphologically distinctive forms may include examples of convergent evolution of derived forms. Alternatively, the common ancestor may have been a polymorphic species that has lost its plasticity in some derived lineages. In an attempt to test the ribosomal phylogeny, we here compare it with a phytogeny based on isozymic variation. The main features of the ribosomal and isozymic phylogenies are similar. The carnivorous (macrostome-forming) species are widely scattered in both, as are the bacteriophagous pyriform species. Isozymic and ribosomal analyses are optimally useful, however, in different contexts. Isozymic variations can distinguish species that are ribosomally identical. Ribosomal variations provide more secure evaluations of distant relationships.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1550-7408.1989.tb02661.x
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  • 2
    Electronic Resource
    Electronic Resource
    Genetic Evidence Concerning the Structure of the Tetrahymena thermophila Macronucleus*† (1979)
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 26 (1979), S. 0 
    Details
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Synopsis.A satisfactory model of the Tetrahymena thermophila macronucleus must explain its genetic behavior in terms of its constituent molecules. Particular genetic phenomena requiring explanation are (a) phenotypic assortment, here interpreted as resulting from allelic disjunction rather than from differential gene expression; (b) unequal allelic input for some loci, interpreted as a consequence of unequal and selective replication of some alleles during early macronuclear development; (c) delayed assortment at some loci, interpreted as an effect of inequality of allelic input combined with a generalized elevation of DNA content during early clonal history; (d) linkage disruption, probably reflecting continuous somatic recombination rather than dissolution of chromosomes into small repliconic units; (e) assortment depression, brought about by the occasional association of homologous replicons (chromosomes) or else by a differential increase in some classes of replicons; (f) ploidy-related developmental differences in macronuclear primordia are interpreted on the basis of quantitative differences in DNA rather than in terms of an early perception of genic imbalance, (g) Ploidy independent macronuclear DNA content is consistent with several models of size regulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1550-7408.1979.tb02722.x
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  • 3
    Electronic Resource
    Electronic Resource
    Crypthecodinium and Tetrahymena: An exercise in comparative evolution (1992)
    Springer
    Journal of molecular evolution 34 (1992), S. 209-218 
    Details
    ISSN: 1432-1432
    Keywords: Dinoflagellate ; Ciliated protozoa ; Ribosomal RNA ; String analysis ; Crypthecodinium ; Tetrahymena ; Glaucoma ; Colpidium ; Lambornella
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Nucleotide sequences have been determined for the highly variable D2 region of the large rRNA molecule for over 60 strains of dinoflagellates. These strains were selected from a worldwide collection that represents all the known sibling species (compatibility groups, Mendelian species) in the sibling swarm referred to as Crypthecodinium cohnii. A phylogenetic tree has been constructed from an analysis of the variations in a length of about 180 bases, using PHYLOGEN string analysis programs. The Crypthecodinium tree is compared with the previously published but here augmented tree constructed upon the same rRNA region for the sibling species of a worldwide collection of ciliated protozoa related to the genus Tetrahymena. The first reported sequence of Lambornella clarki, the parasite of tree-hole mosquitoes, is included. The dinoflagellate species complex is much more homogeneous with respect to ribosomal variation. The mean number of differences among sequences from different Crypthecodinium species is about 7, in comparison with 22 differences among the ciliate species examined. Moreover, all the diversity in the dinoflagellates can be explained by base substitutions, whereas insertions and deletions are common in the ciliates. The dinoflagellates are also much more uniform with respect to nutritional and genetic economies. The two complexes differ also in the relationship between molecular variations and breeding compatibility. All tetrahymenine sibling species thus far examined are monomorphic in the D2 region, but several dinoflagellate species are polymorphic. Several different dinoflagellate species, moreover, have identical D2 regions. This kind of ribosomal identity of incompatible strains is found in these ciliates only in one tight cluster of species—Group C. The tetrahymenine swarm is apparently much older than the Crypthecodinium swarm, and the dinoflagellate species produce incompatible progeny species much more readily than do the ciliates, perhaps by the acquisition of mutations that potentiate incompatibility in sympatric populations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00162970
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  • 4
    Electronic Resource
    Electronic Resource
    Eukaryotic origins: String analysis of 5S ribosomal RNA sequences from some relevant organisms (1991)
    Springer
    Journal of molecular evolution 32 (1991), S. 316-327 
    Details
    ISSN: 1432-1432
    Keywords: 5S rRNA ; String analysis ; Eukaryotes ; Archaebacteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Using the PHYLOGEN tree-forming programs, we evaluate the published 5S rRNA sequences in certain of the files in the Berlin DataBank in an attempt to identify the connection between archaebacteria and the eukaryotic protists. These programs are based on methods of string analysis developed by Sankoff and others. Their discriminatory power is derived from their continuous realignment of sequences through repeated assessment of insertions and deletions as well as substitutions. The programs demonstrate that even these small molecules (ca. 120 bases) retain substantial records of evolutionary events that occurred over a billion years ago. The eukaryotes seem to have been derived from ancestors near the common origins of the halobacterial and Methanococcales groups. Identifying what might have been a primordial eukaryote is more difficult because several of the species considered as early derivatives from the common root are isolated species with large genetic differences from each other and from all other extant forms that have been sequenced. The ameboid, flagellated, and ciliated protists seem to have emerged nearly simulataneously from an ancient cluster, but the sarcodinid protozoa have preference as the group of most ancient origin. The euglenozoa and the ciliates are of later derivation. Our ability to tease plausible trees from such small molecules suggests that the mode of analysis rather than the size of the molecule is often a major limitation in the reconstruction of acceptable ancient phylogenies. The residual uncertainty with respect to the conclusions of the 5S analysis may indicate a real limit on the informational content of such small molecules; the period of evolutionary time during which the primary eukaryotic radiation occurred may have been very short relative to the rate of fixation of changes in this highly conserved molecule. Much of even this limitation may be resolved, however, when a sufficiently dense sample of the problematic taxa is examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02102190
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