Some genetic consequences of skewed fecundity distributions in plants.

Most plant populations show a "skewedrd distribution of fecundity amongst their members, in contrast to the poisson distribution assumed by most population genetical theory. We examine by simulation the consequences of skewed fecundity for plant evolution when combined with sieve selection. In comparison with poisson-based theory, plant populations are likely to show a faster response to selection, especially when the favoured allele is at a low frequency. Selection against a deleterious immigrant allele will also be more effective, reducing its equilibrium frequency in a population. In the special case of heterozygote disadvantage traits will evolve that could not under poisson theory. However, random variation is also higher, giving a 10-plant population an effective population size of about 6.4 under poisson theory. The conclusions are not qualitatively changed by different assumptions on the exact shape of the fecundity distribution, or on heritability, or on reproduction by the smallest plants of the population.