Abstract - American Naturalist 2, 1993

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 9 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 upon 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 non-random. 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.

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