Interruption of Synthesis as a Cost of Sex in Small Organisms

Abstract

Three processes associated with sex-meiosis, gametic union, and nuclear fusion-have a mechanical component, i.e., they require movements of supramolecular bodies. Times required for these processes are surprisingly high, probably because of the mechanical component, thus insuring that production of cells by sexual processes will require much longer than production of an equal number of cells by asexual processes. This is especially evident in direct comparisons of meiosis and mitosis. Meiosis requires much longer than two mitotic divisions. For unicellular organisms, and for small multicellular organisms in which the egg-to-egg time is very short, the additional time required by sexual processes at the cellular level lowers the feasibility of sex by slowing the reproduction rate. This is called the "cellular-mechanical" cost of sex. The cellular-mechanical cost of sex is at least twofold and will often exceed 10-fold by comparison with asexual reproduction in unicellular eucaryotes. The cellular mechanical cost of sex thus is a strong selective force acting against sex in unicellular and small organisms and, because it does not apply when the organism stops growing, tends to restrict sexuality to the end of the growth period.