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  • Anisotropy Computer simulations Electrophysiology Gap junctions Heart Ischemia Ventricular cells  (1)
  • Key words: Silver crucian carp — Gynogenesis — Gonochoristic reproduction — Sex evolution — Genetic recombination — RAPD markers  (1)
  • Pedogenic carbonate  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    Genetic Evidence for Gonochoristic Reproduction in Gynogenetic Silver Crucian Carp (Carassius auratus gibelio Bloch) as Revealed by RAPD Assays (2000)
    Springer
    Journal of molecular evolution 51 (2000), S. 498-506 
    Details
    ISSN: 1432-1432
    Keywords: Key words: Silver crucian carp — Gynogenesis — Gonochoristic reproduction — Sex evolution — Genetic recombination — RAPD markers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Sex evolution has been a debating focus in evolutionary genetics. In lower vertebrates of reptiles, amphibians, and fish, a species or a bioform reproduces either sexually or asexually but never both. A few species were found to consist of all females in fish. These all-female species can propagate by asexual reproduction modes, such as gynogenesis and hybridogenesis. However, the coexistence of sexuality and asexuality in a single species was recently noted only in a cyprinid fish silver crucian carp, Carassius auratus gibelio. This fish had been demonstrated to be capable of gynogenesis stimulated by sperm from other related species. Surprisingly, natural populations of this fish consist of a minor but significant portion (approx. 20%) of males. As different clones with specific phenotypic and genetic characteristics have been found, and RAPD markers specific to each clone have recently been identified, this fish offers many advantages for analyzing whether or not genetic recombination occurs between different clones. In this study, artificial propagation was performed in clone F and clone D. Ovulated eggs from clone F were divided into two parts and respectively inseminated with sperm from a clone D male and from a red common carp (Cyprinus carpio) male. The control clone D individuals were selected from gynogenetic offspring of clone D activated by sperm of red common carp. The phenotype and sex ratio in the experimental groups were also observed. Using RAPD molecular markers, which allow for reliable discrimination and genetic analysis of different clones, we have revealed direct molecular evidence for gonochoristic reproduction in the gynogenetic silver crucian carp and confirmed a previous hypothesis that the silver crucian carp might reproduce both gynogenetically and gonochoristically. Therefore, we conclude that the silver crucian carp possesses two reproductive modes, i.e., gynogenetic and gonochoristic reproduction. The response mechanism of two reproductive development modes may be the first discovery in vertebrates. Additionally, we discuss the evolutionary implication between gynogenetic and gonochoristic reproduction modes and the contribution of the minor proportion of males to genetic flexibility in the gynogenetic silver crucian carp.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002390010113
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Stable isotope ratios of soil carbonate and soil organic matter as indicators of forest invasion of prairie near Ames, Iowa (1993)
    Springer
    Oecologia 95 (1993), S. 365-369 
    Details
    ISSN: 1432-1939
    Keywords: Stable isotope ; Isotope ratios ; Pedogenic carbonate ; Organic matter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Stable isotope ratios of pedogenic carbonate and organic matter were measured in a prairie-transition-forest soil biosequence near Ames, Iowa to determine the vegetation succession. The modern vegetation is dominated by non-native C3 plants which have been introduced by agricultural practices. The δ13C values of soil organic matter from the prairie and forest endmembers indicate C4 and C3 dominated ecosystems, respectively, during the accumulation of soil organic matter. Pedogenic carbonate from all soils, including rare pedogenic carbonate from the forested soil, has an average δ13C of-2.0‰, indicating that the carbonate formed under a C4 vegetation. These results indicate that the ecosystem was a C4-dominated prairie and therefore suggest a recent arrival of forests and other C3 plants in the area. This study also implies that the primary features of the transitional Lester soil series, which has soil properties intermediate between Alfisols and Molisolls, formed under prairie conditions and were overprinted by an invading forest.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00320990
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of anisotropy on the development of cardiac arrhythmias associated with focal activity (2000)
    Springer
    Pflügers Archiv 441 (2000), S. 301-312 
    Details
    ISSN: 1432-2013
    Keywords: Anisotropy Computer simulations Electrophysiology Gap junctions Heart Ischemia Ventricular cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. The anisotropy that normally exists in the myocardium may be either enhanced in peri-infarction zones by loss of lateral cell connections or reduced by redistribution of gap junctions. To test how the degree of anisotropy affects the development of ectopic focal activity, we carried out computer simulations in which a model of an ectopic focus is incorporated as the central element of a two-dimensional sheet of ventricular cells. At low values of intercellular coupling conductance (G c), the focus region is spontaneously active, but the limited intercellular current flow inhibits propagation. At high G c, automaticity is suppressed by the loading effects of the surrounding cells. At intermediate G c, the ectopic activity may propagate into the sheet. In the case of isotropic coupling, the minimum size of the focus region for propagation to occur (in terms of number of collaborating cells within the focus) is as small as approximately ten cells, and this number decreases with increasing anisotropy. Thus, the presence of anisotropy facilitates the development of ectopic focal activity. We conclude that the remodeling that occurs in peri-infarction zones may create a substrate that either facilitates (enhanced anisotropy) or inhibits (reduced anisotropy) the development of cardiac arrhythmias associated with ectopic focal activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240000413
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    Paper (German National Licenses)
    Fulltext
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