Evolution towards self‐compatibility when mates are limited

Abstract

Theory of plant mating system evolution predicts the spread of self‐compatibility (SC) in a predominantly self‐incompatible population when inbreeding depression (ID; the decline in fitness because of selfing) is small and when compatible mates are limited. I tested these two predictions by measuring the occurrence of SC in 13 natural populations of Ranunculus reptans L. that varied in ID and frequency of cross‐incompatible mates. Enforced selfing experiments were conducted in 2 years. In the first year, self‐pollination was applied at two flower ages to investigate the occurrence of delayed SC. I found that SC was not uncommon across all populations, but self‐compatible plants usually produced few seeds. There was no evidence for delayed SC. The occurrence of SC was not associated with population‐level ID, but populations with more limited availability of compatible mates had a significantly higher frequency of plants that were at least partially self‐compatible. The results indicate that, in R. reptans, a shortage of available mates in small populations may cause the evolution of partial SC and mixed mating.

MUTATIONAL MELTDOWN IN SELFINGARABIDOPSIS LYRATA

“…The potential to evolve toward selfing is present in nearly all outcrossing populations because all have some partially or fully self‐compatible individuals that at least partially self (Willi and Määttänen 2010). Other outcrossing species also show evidence that, despite low inbreeding load, self‐compatibility or selfing increases in frequency only during periods of low pollen or mate availability (Kalisz et al 2004; Willi 2009).…”

“…One problem with such comparisons is that even related species differ in their history, ecology, and life history, and these factors may affect levels of inbreeding load. The best data are therefore provided by comparisons within species or lower taxonomic entities (Johnston and Schoen 1996; Vogler et al 1999; Busch 2005; Goodwillie and Knight 2006; Willi 2009).…”

Does Mate Limitation in Self-Incompatible Species Promote the Evolution of Selfing? The Case of Leavenworthia Alabamica

“…In general, most natural populations with gametophytic and sporophytic SI systems have been found to harbor 20–40 S‐alleles. In species with gametophytic SI, significant levels of mate limitation have been observed only in genetically depauperate populations of Ranunculus reptans , which is both tetraploid and clonal (Willi et al 2005), and there is evidence that self‐compatible mutants are more common in mate limited populations of this species (Willi 2009). In contrast, no mate limitation was found in populations with fewer than 10 plants in Pyrus pyraster (Holderegger et al 2008).…”

Benefits of gene flow are mediated by individual variability in self‐compatibility in small isolated populations of an endemic plant species

“…Shifts in the relative proportions of selfing and outcrossing within populations are the result of mating system evolution and the diversity of mating systems in plants is an indicator of the flexibility in responding to selection (Levin, ). Evidence is increasing that the mating system itself may respond adaptively to small population size and fragmentation through breakdown of self‐incompatibility (Busch, Joly, & Schoen, ; Karron et al., ; Stephenson, Good, & Vogler, ; Willi, ). Levin () suggested this breakdown is often due to the action of modifier genes that alter the effectiveness of self‐incompatibility alleles (i.e., pseudo‐self‐fertility, PSF), a critical step in the evolution of self‐fertility.…”