Fisher's automatic advantage of self-fertilization does not apply in cleistogamous species.

Abstract

In hermaphroditic plants, the evolution of self-fertilization is driven by two major forces; the cost of outcrossing or Fisher's automatic advantage of selfing and inbreeding depression. Seminal theoretical works have established that an inbreeding depression threshold of 0.5 governs the evolution. Below that threshold, selfing evolves, above that, outcrossing evolves. Does this threshold apply to cleistogamous plants? I developed a model using a Lloydian approach to analyze the evolution of cleistogamy. I showed that the inbreeding depression threshold does not apply in cleistogamous species, and that because cleistogamous (closed) flowers do not export pollen, Fisher's advantage of selfing is totally cancelled. In line with model predictions, I discuss the fact that cleistogamous species often exhibit low inbreeding depression in empirical studies.