TRANSMISSION ADVANTAGE FAVORS SELFING ALLELE IN EXPERIMENTAL POPULATIONS OF SELF-INCOMPATIBLEWITHERINGIA SOLANACEA(SOLANACEAE)

Abstract

The evolution of self-fertilization is one of the most commonly traversed transitions in flowering plants, with profound implications for population genetic structure and evolutionary potential. We investigated factors influencing this transition using Witheringia solanacea, a predominantly self-incompatible species within which self-compatible genotypes have been identified. We showed that self-compatibility in this species segregates with variation at the S-locus as inherited by plants in F1 and F2 generations. To examine reproductive assurance and the transmission advantage of selfing, we placed self-compatible and self-incompatible genotypes in genetically replicated gardens and monitored male and female reproductive success, as well as selfing rates of self-compatible plants. Self-compatibility did not lead to increased fruit or seed set, even under conditions of pollinator scarcity, and the realized selfing rate of self-compatible plants was less than 10%. Self-compatible plants had higher fruit abortion rates, consistent with previous evidence showing strong inbreeding depression at the embryonic stage. Although the selfing allele did not provide reproductive assurance under observed conditions, it also did not cause pollen discounting, so the transmission advantage of selfing should promote its spread. Given observed numbers of S-alleles and selfing rates, self-compatibility should spread even under conditions of exceedingly high initial inbreeding depression.

Reproductive assurance drives transitions to self-fertilization in experimental Caenorhabditis elegans

“…Instead of individual selection, transitions to androdioecy in natural Caenorhabditis may have resulted from a correlated response to density dependent selection among demes for dispersal to and/or colonization of novel habitats where outcrossing was not necessarily limited [36,37,39]. The lack of a cost of meiosis in Caenorhabditis, since hermaphrodites do not outcross each other, and the existence of a cost of males in outcrossing lineages would then make certain that the first selfing colonizers would outcompete outcrossers reaching the same habitat at a later time, see for example [22] for an empirical example.…”

“…Despite the considerable efforts trying to demonstrate the hypothesis of reproductive assurance, empirical evidence is mixed [18][19][20][21], and whether individual selection can drive the transition to selfing has not been subject to direct experimental tests; but see [22][23][24]. This is partly because hermaphroditism and selfing occur in multiple forms, not all of which clearly assure population persistence in environments with limited opportunity for outcrossing [17,[25][26][27][28].…”

Self-fertilization, sex allocation and spermatogenesis kinetics in the hypodermically-inseminating flatworm Macrostomum pusillum

“…Various factors have been suggested to favour the evolution of selfing (Goodwillie et al, 2005), but most research to date has focused on two main aspects (Busch and Delph, 2012). First, as initially proposed by Fisher (1941) and recently confirmed experimentally in a plant species (Stone et al, 2014), a gene responsible for selfing should automatically be selected and thus increase in frequency when emerging in a primarily outcrossing population because of its higher transmission rate (transmission advantage hypothesis). Second, from an ecological perspective, selfing can act as a reproductive assurance mechanism when mate availability is low (Darwin, 1876;Jain, 1976), as is the case for many organisms (e.g.…”

Costs of selfing prevent the spread of a self‐compatibility mutation that causes reproductive assurance

“…With a preponderance of recent transitions to selfing across many independent branches of the angiosperm phylogeny, there is ample raw material to address some of these questions (Goldberg et al 2012;Shimizu and Tsuchimatsu 2015). Study systems with intraspecific polymorphism in the degree of self-fertilization are particularly valuable to challenge hypotheses for the initial spread of mutations that cause shifts to partial self-fertilization in outcrossing populations (Stone et al 2014;Herman and Schoen 2016).…”

“…The spread of SC mutations that cause selfing at the S-locus involves an additional process beyond those that operate on selfing mutations in general. The corresponding outcross siring advantage enjoyed by SC mutations depends on the number of S-alleles, and can be estimated by comparing the success of SI and SC genotypes through outcross pollen (Busch and Schoen 2008;Stone et al 2014). This arises because pollen bearing functional S-alleles cannot fertilize ovules born by plants with matching specificities in the population-S-alleles cause plants to be both self-and cross-incompatible (Wright 1939;Vallejo-Marin and Uyenoyama 2004).…”