Summary
Two single-locus deterministic models are constructed for the maintenance of genetic variability in localised plant populations. In the first model, it is supposed that self-pollination is complete, heterozygotes are absent, and only seeds disperse. Then the ploidy is arbitrary. In the second, it is assumed that the plants are diploid, cross-pollination is total, and only pollen disperse. Explicit conditions for a protected polymorphism are derived for each model in the diallelic two-niche case. These conditions are simplified, displayed graphically, and discussed extensively for directional selection for different alleles in the two niches. If the amount of seed dispersal is divided by two, the criteria for a protected polymorphism in the self-pollinating scheme become identical to the criteria in the cross-pollinating situation with no multiplicative dominance. The restrictions that must be placed on the fitnesses for a protected polymorphism always become more stringent as the amount of dispersion increases. If the dispersion rate is not very close to zero and the selection coefficients are very small, the protection conditions reduce to overdominance for the mean fitnesses in the habitat. Unless there is complete dominance, protection always exists with fixed fitnesses for sufficiently low non-zero dispersal. For any amount of dispersion, there is always protection in the second model if, in each niche, the fitness of the deleterious homozygote is less than that of the heterozygote.
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Supported by the National Science Foundation (Grant No. DEB76-01550).
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Nagylaki, T. Dispersion-selection balance in localised plant populations. Heredity 37, 59–67 (1976). https://doi.org/10.1038/hdy.1976.65
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DOI: https://doi.org/10.1038/hdy.1976.65
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