Inbreeding Effects in Clarkia tembloriensis (Onagraceae) Populations with Different Natural Outcrossing Rates

Abstract

Inbreeding depression is commonly observed in natural populations. The deleterious effects of forced inbreeding are often thought to be less pronounced in populations with self‐pollinating mating systems than in primarily outcrossing populations. We tested this hypothesis by comparing the performance of plants produced by artificial self‐ and cross‐pollination from three populations whose outcrossing rate estimates were 0.03, 0.26, and 0.58. Outcrossing rates and inbreeding coefficients were estimated using isozyme polymorphisms as genetic markers. Analysis of F statistics suggests that biparental inbreeding as well as self‐fertilization contribute to the level of homozygosity in the seed crop. Biparental inbreeding will reduce the heterozygosity of progeny produced by outcrossing, relative to random outcrossing expectations, and hence will reduce the effects of outcrossing versus self‐fertilization. Heterotic selection may increase the average heterozygosity during the life history. Selfed and outcrossed seeds from all three populations were equally likely to germinate and survive to reproduce. However, inbreeding depression was observed in fecundity traits of plants surviving to reproduction in all three populations. Even in the population whose natural self‐fertilization rate was 97%, plants grown from seed produced by self‐pollination produced fewer fruits and less total seed weight than plants grown from outcrossed seed. There was no detectable inbreeding depression in estimated lifetime fitness. Inbreeding effects for all reproductive yield characters were most severe in the accession from the most outcrossing population and least severe in the accession from the most self‐fertilizing population.

The Relative Importance of Inbreeding and Maternal Sex in Determining Progeny Fitness in Sidalcea oregana SSP. Spicata, A Gynodioecious Plant

“…Other studies that have followed the fates of inbred and outbred plants through to reproductive maturity also found significant effects on reproductive output (see Table 3, p. 253 in Charlesworth and Charlesworth, 1987;Kalisz, 1989;Dudash, 1990;Holtsford and Ellstrand, 1990; but see Clay and Antonovics, 1985). The only juvenile character that was significantly affected by inbreeding level was relative growth rate; selfed offspring grew 11 % slower per day than either sib-crossed or outcrossed offspring.…”

The effects of phenological mismatches on demography

“…Phenology may also play an important role in intraspecific interactions. For outcrossing plants, it is often important that many individuals of a particular species in an area flower synchronously to maximize the likelihood of cross-pollination, which can have important fitness benefits (Holtsford & Ellstrand 1990). Populations of dioecious species of plants for which males and females are spatially segregated along an environmental gradient (Bierzychudek & Eckhart 1988;Dawson & Ehleringer 1993) could be at risk if the spatial segregation starts to correspond to phenological segregation as well.…”

Multiple Origins of Self-Compatibility in Linanthus Section leptosiphon (Polemoniaceae): Phylogenetic Evidence from Internal-Transcribed-Spacer Sequence Data

“…Recent phylogenetic studies show that selling has arisen multiple times within a single genus or family (Kohn et al 1996;Schoen et al 1997). Indeed, variation in mating systems is present among populations of many plant species (Lloyd 1965;Moore and Lewis 1965;Schoen 1982;Wyatt 1986;Holtsford and Ellstrand 1990;Johnston and Schoen 1996), and selling variants have been shown to have multiple independent origins at that taxonomic scale (Lloyd 1965;Wyatt 1988;Husband and Barrett 1 1993). Selective explanations put forth for the evolution of selling include two predominant, nonexclusive hypotheses: the automatic transmission advantage of a selling gene (Fisher 1941) and selection for reproductive assurance under conditions where pollinators are scarce or unpredictable (Stebbins 1957).…”