Some Reproductive Factors Affecting the Selection of Self-Fertilization in Plants

Abstract

The fitnesses of two phenotypes which differ in their frequency of self-fertilization are expressed exactly in terms of various parameters, including the relative fitness of progeny from selfing, i, and the proportion of available ovules fertilized with the aid of an external agent, e. Strategic models of natural selection find stationary conditions where the two phenotypes have the same fitness. Conditions when selfing is advantageous to populations and to individuals are not usually identical. Conditions favoring self-fertilization are more stringent when selfing competes with crossing (for individual selection, i > 1/2) and less stringent when selfing occurs prior to crossing (i > e/2). When selfing is delayed until after all opportunities for crossing, it is always advantageous if the parameters vary independently. Some functional interactions between parameters, as when an increase in selfing simultaneously reduces the efficiency of external pollinating agents, result in stationary conditions with mixed self- and cross-fertilization under certain conditions. Following a change in the level of self-fertilization, certain evolutionary adjustments increase the advantage of the acquired mode of fertilization. The models demonstrate that the evolution of various levels of self-fertilization in plants can be explained by individual selection without recourse to postulates of long-term advantages to populations.