Selection in plant populations of effectively infinite size VI. Overlapping generations

Abstract

A selection model for iteroparous, monoecious, or hermaphroditic plant populations is considered which encompasses viabilities, pollen fertilities, ovule fertilities, and rates of self-fertilization which may arbitrarily depend on both age and genotype. The general conditions for establishment (which are also those for protectedness) of an allele are derived. The classical conjecture that the conditions of protectedness are the same for separated and overlapping generations if the intrinsic rates of increase are applied is discussed. For this purpose it is necessary to introduce two new intrinsic values: the intrinsic rate of self-fertilization and the intrinsic pollen-to-ovule ratio. The significance of the intrinsic values is demonstrated for complete self-fertilization, selection restricted to differential, partial self-fertilization, and sexual asymmetry (absence of proportionality between pollen and ovule production), including selection restricted to one sex. With the exception of asymmetric selection in both sexes, it turns out that the intrinsic values suffice to state the conditions for protectedness, but more information about the life histories is required to determine the exact speed of establishment. For asymmetric selection in both sexes, the concept of intrinsic value is inadequate for investigating the problem of establishment and thus the evolution of life histories. Since sexual asymmetry is rather the rule than the exception and selfing is common in plants, the consequences for finding optimal life histories are outlined.