The effects of recurrent clonal formation on clonal invasion patterns and sexual persistence: a Monte Carlo simulation of the frozen niche-variation model.

The interaction of sexual and asexual organisms in a heterogeneous environment was explored using a Monte Carlo simulation. The model was designed to address sexual persistence and the pattern of clonal invasion in a species that periodically produces clonal mutants. The parameters of the model were the mutation rate of outcrossed sexuals to obligate asexuality, the number of progeny per parent, the within-genotype niche width, and the carrying capacity for nine separate resources. The inclusion of recurrent clonal invasion due to meiosis-disrupting mutations drove the sexual species extinct in temporally stable environments, at a rate dependent on the mutation frequency, sexual niche breadth, and the relative magnitude of the number of progeny per parent and the carrying capacity. In simulations with uniform resource distributions, clonal invasion was distinctly nonrandom. The pattern of clonal invasion was "centripetal'': mutant clones that captured or "froze" the rarely recombined (or marginal) sexual phenotypes were more successful initially than clones freezing frequently recombined (or central) sexual phenotypes. The long-term persistence of the sexuals was confined to simulations that included temporal resource fluctuations. In such instances, sexuals and asexuals coexisted in a mutation/extinction equilibrium, where asexuals were continually produced by mutation and lost by short-term random extinctions. Increased within-genotype niche width reduced the probability of clonal extinction and thus restricted the likelihood of sexual/clonal coexistence.