The Effective Size of Mixed Sexually and Asexually Reproducing Populations

Corresponding author: Katsuei Yonezawa, Kyoto Sangyo University, Kamigamo, Kita-ku, Kyoto 603-8555, Japan., yonezaw{at}cc.kyoto-su.ac.jp (E-mail)

Communicating editor: T. H. D. BROWN

Using the transition matrix of inbreeding and coancestry coefficients, the inbreeding (N_eI), variance (N_eV), and asymptotic (N_e) effective sizes of mixed sexual and asexual populations are formulated in terms of asexuality rate (), variance of asexual (C) and sexual (K) reproductive contributions of individuals, correlation between asexual and sexual contributions (_ck), selfing rate (ß), and census population size (N). The trajectory of N_eI toward N_e changes crucially depending on , N, and ß, whereas that of N_eV is rather consistent. With increasing asexuality, N_e either increases or decreases depending on C, K, and _ck. The parameter space in which a partially asexual population has a larger N_e than a fully sexual population is delineated. This structure is destroyed when N(1 – ) < 1 or > 1 – 1/N. With such a high asexuality, tremendously many generations are required for the asymptotic size N_e to be established, and N_e is extremely large with any value of C, K, and _ck because the population is dominated eventually by individuals of the same genotype and the allelic diversity within the individuals decays quite slowly. In reality, the asymptotic state would occur only occasionally, and instantaneous rather than asymptotic effective sizes should be practical when predicting evolutionary dynamics of highly asexual populations.