The genetic basis of selfing rate evolution

Abstract

Evolution of selfing is common in plant populations, but the genetic basis of selfing rate evolution remains unclear. Although the effects of genetic properties on fixation for mating‐unrelated alleles have been investigated, loci that modify the selfing rate (selfing modifiers) differ from mating‐unrelated loci in several aspects. Using population genetic models, I investigate the genetic basis of selfing rate evolution. For mating‐unrelated alleles, selfing promotes fixation only for recessive mutations, but for selfing modifiers, because the selection coefficient depends on the background selfing rate, selfing can promote fixation even for dominant modifiers. For mating‐unrelated alleles, the fixation probability from standing variation is independent of dominance and decreases with an increased background selfing rate. However, for selfing modifiers, the fixation probability peaks at an intermediate selfing rate and when alleles are recessive, because a change of its selection coefficient necessarily involves a change of the inbreeding coefficient, because both depend on the level of inbreeding depression. Furthermore, evolution of selfing involving multiple modifier loci is more likely when selfing is controlled by few large‐effect rather than many slight‐effect modifiers. I discuss how these characteristics of selfing modifiers have implications for the unidirectional transition from outcrossing to selfing and other empirical patterns.

The role of self-fertilization in plant colony establishment

“…However, plasticity can inhibit the effectiveness of a higher selfing rate in the source population and selfing rate evolution in promoting colony establishment, perhaps because plasticity reduces their importance in providing reproductive assurance. Moreover, plasticity, by increasing the background selfing rate, may reduce the selective strength on selfing modifiers and thus inhibit selfing rate evolution (Xu 2022b).…”

“…Moreover, plasticity can inhibit selfing rate evolution, which can be seen by comparing the rate of selfing rate evolution at rows with 𝑢 = 0,0.25,0.5 in Table 3. This is because a higher background selfing rate reduces the selective strength on selfing modifiers (Xu 2022b).…”

Effects of selfing on the evolution of sexual reproduction

“…Previous subsections focus on indirect selection on a sex modifier caused by selection at fitness loci. To quantify how selfing can reduce the strength of selection against sex by lowering the cost of meiosis and providing reproductive assurance under mate limitation, I define the strength of mate limitation 𝜏 as the reduced proportion of outcrossed ovules (Xu 2022). Therefore, the relative fertility via outcrossing is 1 − 𝜏 compared to selfing and asexual reproduction.…”