Ref ID : 4644
Hans Peter Duerr, Martin Eichner, and Dieter Ammermann; Modeling Senescence in Hypotrichous Ciliates. Protist 155:45-52, 2004
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Asexually reproducing hypotrichous ciliates undergo senescence which is in general attributed to degenerative processes in the macronucleus, assuming that loss of viability is based on loss of genetic elements. It is generally accepted that the genetic elements in the macronucleus of hypotrichs segregate randomly, a process which potentially can lead to aneuploid imbalances in the distribution of gene copies. It is, however, unclear whether there are mechanisms which compensate for such imbalances such that each genetic element regains its predetermined copy number (regulatory model, conserving euploidy), or whether the genetic elements only double, so that genetic imbalances can be inherited to further generations (stochastic model, allowing aneuploidy). By means of mathematical modeling and simulations, we investigate these two models with respect to the number of generations a lineage of hypotrichs can survive under asexual conditions. Whereas the regulatory model cannot explain senescence in hypotrichs, the stochastic model provides plausible results which, however, strongly depend on the assumed distribution of copy numbers which we investigate by means of three examples. For both models, simple prediction formulae of the approximate survival time of asexually reproducing ciliates are provided.