Sex promotes gamete selection: A quantitative comparative study of features favoring the evolution of sex

Explaining the maintenance of sexual reproduction remains one of the greatest challenges in biology. The theoretical oddity of sex is based on at least three advantages that asexual organisms have over sexual ones: 1Asexuals, by not producing males, have a two fold advantage over sexuals, regarding the number of reproductive individuals; 2Sexuals have an evolutionary disadvantage over asexuals, in that a rare alleles that increases fitness of one parent, for example, is not necessarily transmitted to the offspring, due to segregation. 3Asexuals do not have to find a mate in order to reproduce. Here I present the results of evolutionary tournaments performed using the agent based computer simulation Biodynamica. The tournaments explored the relative merits of various features that have been proposed to affect the putative advantages of sexual reproduction, including ploidy, mate selection, large reproductive variance of males, low mutation rates, gamete selection, reduced cost for the production of males, thelytoky vs. parthenogenesis, variable environments and complex genomes. The model allowed for a quantitative comparison of the effect of these features on the adaptive value of sex. The results showed that the production of large number of gametes (for example “masting” in massive flowering of trees or spermatozoa of most animals) inducing gamete selection, together with: non random mate selection, increased variance in male reproductive success and/or low mutation rates, allowed sexual agents to out-breed asexual ones, despite the three disadvantages for sex cited above. The wok suggests that gamete cycles and alloiogenesis, common to most sexual plants, fungi and animals, should be viewed as a new level for natural selection to work. Mate and gamete selection are more efficient in the use of biomass, energy and time, than natural selection at the level of organisms, helping to make sexual reproduction an evolutionary success.