Selection for pollen competitive ability in mixed-mating systems

Abstract

Coexpression of genes in plant sporophytes and gametophytes allows correlated gametic and sporophytic selection. Theory predicts that, under outcrossing, an allele conferring greater pollen competitive ability should fix within a population unless antagonistic pleiotropy with the sporophyte stage is strong. However, under strong selfing, pollen competitiveness is immaterial as superior and inferior competitors are deposited on opposite stigmas, producing assortative competition. Because many plant species have mixed-mating systems, selfing should be critical in the spread and maintenance of pollen-expressed genes affecting competitiveness. We present two one-locus, two-allele population genetic models for the evolution of a locus controlling pleiotropic antagonism between pollen competitiveness and diploid fitness. Analytical solutions provide minimum and maximum selfing rates allowing invasion of alleles with greater diploid and haploid fitness, respectively. Further, polymorphism is only maintained when diploid selection is recessive. Fixation of the allele conferring greater pollen competitiveness may be prevented, even with weak sporophytic counterselection, with sufficiently high selfing. Finally, selfing expands and limits the range of haploid-diploid selection coefficients allowing polymorphism, depending on dominance and selfing mode.

Reproductive transitions in plants and animals: selfing syndrome, sexual selection and speciation

“…Haploid gene expression in pollen means that selfers may nevertheless experience pollen competition as an extra source of selection against new deleterious mutations on top of selection in sporophytes (Dapper & Wade, ). Specifically, pollen competition in predominant selfers may disfavour low‐quality self‐pollen harbouring deleterious alleles that might otherwise exacerbate inbreeding depression or deleterious mutation accumulation (in the absence of antagonistic effects between gametophyte and sporophyte) (Peters & Weis, ); but see (Damgaard et al ., ). This idea also is related to the ‘selection‐arena hypothesis’ (Stearns, ), and its effectiveness might be limited by low pollen production within a selfing flower.…”

Balancing selection in self‐fertilizing populations

“…2012). Equation (26) shows that selfing reduces haploid selection by two ( term) because male haploid selection is ineffective under selfing and female haploid selection is unchanged (see also Peters and Weis 2018, for more specific selection schemes).…”

“…NA = not applicable. References—1 = Hayman (1953); 2 = Weir (1970); 3 = Kimura and Ohta (1971); 4 = Rocheleau and Lessard (2000); 5 = Hedrick (1998); 6 = Jordan and Connallon (2014); 7 = Tazzyman and Abbott (2015); 8 = Peters and Weis (2018); 9 = Glémin (2010); 10 = Fishman and Kelly (2015); 11 = Jain and Jain (1970); ts = this study (indicated when new results are provided, not only rederived); * = More precisely, the case studied in 8 is male haploid/sex‐independent diploid antagonism.…”

Gametophytic competition games among relatives: When does spatial structure select for facilitativeness or competitiveness in pollination?

“…Selective advantage of facilitativeness (costly to male) versus competitiveness (costly to female) may differ between the perspectives of paternal versus maternal plants (sexual conflict; Arnqvist & Rowe, ; Delph & Havens, ). Possible outcomes of such conflicts can be sensitive to the degree of self‐fertilization, as suggested in both empirical (Brandvain & Haig, ; Cailleau, Grimanelli, Blanchet, Cheptou, & Lenormand, ; Raunsgard et al, ) and theoretical studies (Jordan & Connallon, ; Peters & Weis, ). Especially in the context of intersexual interactions in spatially subdivided plant populations, I would propose that the interplay between the reproductive system (or mating system) and sexual conflict are of critical importance, although these are relatively unexplored in previous studies.…”