Consequences of inbreeding for offspring fitness and gender in Silene vulgaris, a gynodioecious plant

Abstract

In gynodioecious plants, hermaphrodite and female plants co-occur in the same population. In these systems gender typically depends on whether a maternally inherited cytoplasmic male sterility factor (CMS) is counteracted by nuclear restorer alleles. These restorer alleles are often genetically dominant. Although plants of the female morph are obligatorily outcrossing, hermaphrodites may self. This selfing increases homozygosity and may thus have two effects: (1) it may decrease fitness (i.e. result in inbreeding depression) and (ii) it may increase homozygosity of the nuclear restorer alleles and therefore increase the production of females. This, in turn, enhances outcrossing in the following generation. In order to test the latter hypothesis, experimental crosses were conducted using individuals derived from four natural populations of Silene vulgaris, a gynodioecious plant. Treatments included selffertilization of hermaphrodites, outcrossing of hermaphrodites and females using pollen derived from the same source population as the pollen recipients, and outcrossing hermaphrodites and females using pollen derived from different source populations. Offspring were scored for seed germination, survivorship to flowering and gender. The products of self-fertilization had reduced survivorship at both life stages when compared with the offspring of outcrossed hermaphrodites or females. In one population the fitness of offspring produced by within-population outcrossing of females was significantly less than the fitness of offspring produced by crossing females with hermaphrodites from other populations. Self-fertilization of hermaphrodites produced a smaller proportion of hermaphroditic offspring than did outcrossing hermaphrodites. Outcrossing females within populations produced a smaller proportion of hermaphrodite offspring than did crossing females with hermaphrodites from other populations. These results are consistent with a cytonuclear system of sex determination with dominant nuclear restorers, and are discussed with regard to how the mating system and the genetics of sex determination interact to influence the evolution of inbreeding depression.

Genetic determination of male sterility in gynodioecious Silene nutans

“…Such costs have found experimental support in some gynodioecious species (for example Bailey, 2002;Dufay et al, 2008;Del Castillo and Trujillo, 2009), but spatial match between CMS and associated restorers is still debated. Better restoration is found in within-compared with between-population crosses in Thymus vulgaris (Belhassen et al, 1991;Gigord et al, 1998) but not Silene vulgaris (Emery and McCauley, 2002;Bailey and McCauley, 2005), and the level of restoration does not decrease with geographic distance in between-population crosses (Gigord et al, 1998;Bailey and McCauley, 2005). Moreover, restorers were found to be maintained outside of the geographical distribution of their associated CMS in P. coronopus (van Damme et al, 2004) and no correlation was found between CMS and restorer frequencies in Beta vulgaris ssp.…”

Consequences of prairie fragmentation on the progeny sex ratio of a gynodioecious species, Lobelia spicata (Campanulaceae)

“…A recent study of S. vulgaris (nucleocytoplasmically determined gynodioecy) found increased frequency of female progeny from selfed hermaphrodites (Emery and McCauley, 2002). The nuclear restorer alleles act as a dominant allele; thus, selfing increases the frequency of homozygous recessive genotypes and the number of females (Emery and McCauley, 2002).…”

Sex-Ratio Evolution in Nuclear-Cytoplasmic Gynodioecy When Restoration Is a Threshold Trait

“…However, this adjustment of the model would not capture the possible synergies between inbreeding depression and sex. Several researchers have shown that selffertilized hermaphrodites produce higher frequencies of females than outcrossed hermaphrodites (Emery and McCauley 2002;Bailey and McCauley 2005;Glaettli and Goudet 2006). Emery and McCauley (2002) argue that females are more common among offspring produced by self-fertilization because restorer alleles tend to be dominant; thus, self-fertilization increases female frequencies via the increased production of homozygous recessive genotypes.…”

“…Several researchers have shown that selffertilized hermaphrodites produce higher frequencies of females than outcrossed hermaphrodites (Emery and McCauley 2002;Bailey and McCauley 2005;Glaettli and Goudet 2006). Emery and McCauley (2002) argue that females are more common among offspring produced by self-fertilization because restorer alleles tend to be dominant; thus, self-fertilization increases female frequencies via the increased production of homozygous recessive genotypes. Therefore, David McCauley has suggested (personal communication to M. Bailey) that average female fitness could decline relative to hermaphrodite fitness in self-compatible populations because the majority of females would be the result of self-fertilization and suffer from inbreeding depression.…”