Evolution of mixed mating: Effects of among-parent variation in early-acting inbreeding depression coupled with overproduction of ovules

Abstract

Theoretical models were developed to propose a new mechanism enhancing mixed mating (reproduction by both outcrossing and selfing) in hermaphroditic plants; mixed mating can be maintained if there exists among-parent variation in early-acting inbreeding depression in embryos and parents can replace dead embryos by overproduction of ovules. In the two main models developed, the number of embryos produced is allowed to evolve, parents may overproduce embryos, and among-parent variation in early-acting inbreeding depression does not exist or exists. I found that mixed mating does not evolve if among-parent variation in early-acting inbreeding depression does not exist, whereas it evolves if it exists. If the degree of early-acting inbreeding depression in embryos is variable among parents, parents with the same selfing strategy suffer different effects of early-acting inbreeding depression. Specifically, overproduction of embryos may be insufficient when inbreeding depression is severe but wasteful when it is weak. Hence, it is advantageous to produce a moderate number of embryos to reduce waste of resources. Mixed mating is then advantageous to avoid great reductions in seed number caused by massive loss of selfed embryos in cases of severe inbreeding depression.