XIII.3.4.2 Sexual reproduction of the host can develop as an adaptive trait of a parasite

The F-plasmid of bacteria can serve as a prototype for such emergence of a sexual process.This plasmid contains genes encoding the formation of a sex pilus, through which bacteria containing an F-plasmid attach to another bacterial cell and the genes ensure transfer of a copy of the F-plasmid by this pilus to the cells of the recipient.Because the plasmid is capable of integrating into the bacterial DNA or is capable of integrating part of this DNA into itself, it can cause the transfer of bacterial genes during its transfer from cell to cell.Thus, it can be considered to be an adaptive structure that facilitates sexual reproduction for the bacterial cell.Similarly, however, the F-plasmid can be considered to be an infectious agent, a kind of bacteriophage, that has learned not to damage its host cell and that “doesn’t want anything else” than its own reproduction and spreading in the bacterial population.Integration into the bacterial DNA and transfer of bacterial genes thus can constitute only secondary improvement of the effectiveness of the process of plasmid reproduction.A plasmid that integrates into itself, for example, a gene for resistance to antibiotics (R-plasmid) or that is capable of being useful for the bacterial cell in some other way is, of course, at a substantial selection advantage compared to the original F-plasmid.

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The classical Darwinian theory of evolution can explain the evolution of adaptive traits only in asexual organisms. The frozen plasticity theory is much more general: It can also explain the origin and evolution of adaptive traits in both asexual and sexual organisms Read more
Draft translation from: Evoluční biologie, 2. vydání (Evolutionary biology, 2nd edition), J. Flegr, Academia Prague 2009. The translation was not done by biologist, therefore any suggestion concerning proper scientific terminology and language usage are highly welcomed. You can send your comments to flegratcesnet [dot] cz. Thank you.