Female fertility and mating type effects on effective population size and evolution in filamentous fungi.
The idealized individual in many fungal species is a haploid self-sterile hermaphrodite that may be propagated by asexually produced spores or that may reproduce sexually. In field populations, polymorphism occurs for female-sterile/hermaphrodite status, and female-sterile mutants, which function only as males during sexual reproduction, may comprise > 50% of the population. The effective population number may be based on the number of strains of different mating type or the relative frequency of hermaphrodites. The female-sterile mutants are at a selective disadvantage every time sexual reproduction occurs, and must have an advantage during vegetative propagation to persist at a significant frequency. When a high frequency of female-sterile strains is observed in field populations, it indicates that vegetative propagation is a significant component of the fungus' natural history. Depending on the mutation rate to female sterility and the selective advantage of the female-sterile strains during vegetative propagation, the ratio of sexual:asexual generations can range from 1:15 to 1:2300 for species in the Gibberella fujikuroi complex. The relative rarity of sexual reproduction may permit female-sterile strains to accumulate to a level such that local populations could completely lose sexuality and appear as asexual (imperfect) species.
Department of Plant Pathology, Kansas State University, Manhattan 66506-5502, USA. jfl@plantpath.ksu.edu
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JF
Leslie
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Klein
D001203:Ascomycota / Q000235:genetics; D005075:Biological Evolution; D005298:Fertility; D005874:Gibberella / Q000235:genetics*; D008432:Mathematical Computing; D008957:Models, Genetic; D009491:Neurospora / Q000235:genetics*