Sexual Reproduction and Viability of Future Offspring

"The present work is based on an earlier model (suggested in Weinshall 1986), which was further developed (in Weinshall and Eshel 1987) in order to solve some theoretical problems mentioned above, namely, the evolution of sexual reproduc- tion in the face of asexual advantage in fertility. It was shown that if a population composed of fully sexual and fully asexual individuals is exposed to a succession of three or more parasites (or seasons), if, for any parasite, there is a specific allele responsible for the immunity of its carrier against it, and if the death toll of the individuals that are not immune is sufficiently high, then a sexually reproducing subpopulation will always increase in frequency, independent of the cost of sex. Moreover, allowing partially sexual reproduction and assuming that the rate of sexuality, T, is determined by a second modifier locus, we have shown that for any cost of sex, ,u, and for any rate of recombination, r, between the two loci, there is a positive unbeatable rate of sexuality, T = T(r,pu), which is a (unique) evolu- tionarily stable strategy (cf. Hamilton 1967). Likewise, if the rate of sexuality in the population is ao $ T, then any mutant that determines (as a heterozygote) a rate closer to T will be established in the population. Depending on ,u and r, T may be 1 (full sexuality)". (from the article).