A comparison of male and female responses to inbreeding in Cucurbita pepo subsp. texana (Cucurbitaceae)

Accurate estimates of inbreeding depression are necessary in order to predict the evolutionary dynamics of a population, but many studies estimate inbreeding depression based solely on components of female function such as fruit set, seed set, and seed quality. Because total fitness is achieved through both male and female functions in hermaphroditic plants, estimates of both male and female fitness are needed to estimate accurately the magnitude of inbreeding depression. Seedlings of a wild gourd, Cucurbita pepo subsp. texana, with coefficients of inbreeding of 0 and 0.75 were planted in an experimental garden, and several components of male and female fitness were measured over the course of the growing season. Fitness in inbred plants was confounded by both maternal and genetic inbreeding effects. Inbred individuals produced significantly fewer fruits than outcrossed individuals, and percentage germination of seeds from inbred individuals was significantly lower than seeds from outcrossed individuals. Inbred plants also produced significantly fewer staminate flowers and marginally fewer and smaller pollen grains per flower. Pollen from inbred plants also grew significantly more slowly in vitro than pollen from outcrossed plants. Multiplicative estimates of inbreeding depression revealed inbreeding depression for both male and female functions in wild gourd, but inbreeding depression through female function was stronger than inbreeding depression through male function.     

Inbreeding effects on blossom volatiles in Cucurbita pepo subsp. texana (Cucurbitaceae)

Self-pollination by plants gives rise to inbreeding depression. There is increasing recognition that plant inbreeding can have significant implications for interactions between plants and other organisms, including insects and pathogens. Many of these interactions are mediated by plant-derived volatiles, but the effects of inbreeding on volatile production have not previously been investigated. We examined variation in flower volatile production by the wild gourd Cucurbita pepo subsp. texana as a function of inbreeding, sex of the flower, and maternal line. We compared first-generation selfed progeny to outcrossed progeny to assess variation in blossom volatiles due to mating system. Our data indicate that self-pollination reduces total volatile production and changes the relative composition of individual compounds released by C. pepo subsp. texana blossoms. These findings have potentially important implications for interactions between C. pepo subsp. texana and its pollinators and herbivores-including diabroticite cucumber beetles, which vector the bacterial pathogen Erwinia tracheiphila-because previous studies have shown that a number of the individual compounds that vary with inbreeding level can influence insect behavior. We also found significant differences between the volatile profiles of male and female flowers and across maternal families.     

Inbreeding influences herbivory in <Emphasis Type="Italic">Cucurbita pepo</Emphasis> ssp. <Emphasis Type="Italic">texana</Emphasis> (Cucurbitaceae)

In a series of field experiments Diabrotica beetle herbivory was found to influence the magnitude of inbreeding depression in Cucurbita pepo ssp. texana, an annual monoecious vine. Beetles damage flowers and fruits and chew dime-sized holes in leaf tissue between major veins. Inbred plants were found to be more likely to be damaged by beetles and to have more leaves damaged per plant than outcrossed plants. A positive linear association was found between the coefficient of inbreeding and the magnitude of leaf damage, whereas a negative association was found between coefficient of inbreeding and several male and female fitness traits. When pesticides were used to control beetle herbivory, the interaction between coefficient of inbreeding and pesticide treatment was significant for fruit production and marginally significant for pollen quantity per anther. Therefore, the magnitude of inbreeding depression in C. pepo ssp . texana varies depending on the severity of beetle herbivory.     

Outcrossing increases infection success in the holoparasitic mistletoe <Emphasis Type="Italic">Tristerix aphyllus</Emphasis> (Loranthaceae)

Most studies on the fitness advantage of outbreeding in host–parasite systems have been assessed from the host rather than the parasite perspective. Here, we performed experimental pollination treatments to evaluate the consequences of outbreeding on fitness-related traits in the holoparasitic mistletoe Tristerix aphyllus in a 2-year field study. Results indicate that self-pollinated plants had a lower fruit production than outcrossed plants (20.4% and 29.5% reduction in 2002 and 2003, respectively), and resulting inbred fruits were smaller than outcrossed fruits in both years. No effect was detected for seed mass. The percentage of germination of inbred seeds was 15.1% and 6.0% lower than outcrossed seeds in 2002 and 2003, respectively. Inbred seedlings had shorter radicles, which translated to a 71.6% and 60.0% reduction in infection success compared with outcrossed plants in 2002 and 2003, respectively. Overall, our results revealed significant inbreeding depression on almost every trait that was examined. Although the mean value of traits varied from a year to another, the magnitude of inbreeding depression did not change significantly between years. Our findings constitute the first evidence that outcrossing increases infection success and probably virulence in parasitic plant populations.     

Testing for stress-dependent inbreeding depression in Impatiens capensis (Balsaminaceae)

The relevance of inbreeding depression to the persistence of plant populations can depend upon whether stress magnifies inbreeding depression for fitness-related traits. To examine whether drought stress exacerbates inbreeding depression in gas exchange traits and biomass, we grew selfed and outcrossed progeny of inbred lines from two populations of Impatiens capensis in a greenhouse experiment under water-limited and moist soil conditions. Drought stress did not magnify the degree of inbreeding depression for any of the traits measured. In fact, in one population there was a trend for stronger inbreeding depression under well-watered, benign conditions. Furthermore, significant inbreeding depression for carbon assimilation rate and stomatal conductance was only detected in the lines from one population. In contrast, inbreeding depression for biomass was detected within both populations and differed among lines. Drought stress exerted significant selection on physiological traits, favoring increased carbon assimilation rates and decreased stomatal conductance in drought-stressed plants. Patterns of selection did not differ between inbred and outcrossed plants but did differ marginally between populations. Thus, estimates of selection were not biased by the mixed mating system per se, but may be biased by combining individuals from populations with different histories of selection and inbreeding.     

Inbreeding alters a plant-predispersal seed predator interaction

The effect of inbreeding on genetic diversity is expected to decrease plant defences or vigour-related traits that, in turn, can modify the pattern of attack by herbivores. The selective damage caused by herbivores can produce variable fitness costs between inbred and outcrossed progenies influencing the evolution of a species’ plant mating system. By exposing inbred and outcrossed plants to natural conditions of seed predation, we assessed whether inbreeding increases weevil incidence and infestation, and how weevil seed predation affects the fitness of inbred and outcrossed progeny. To test if inbreeding affected the host’s plant quality, we weighed the biomass of weevils developed in inbred and outcrossed progenies. An additional experiment was carried out to examine whether weevils preferentially attack vigorous plants regardless from the level of inbreeding. The average value of leaf size was 21% larger in outcrossed plants than in inbred plants. Likewise, weevil incidence and infestation were 13 and 40%, respectively, higher on outcrossed plants relative to their inbred counterparts. However, the relative impact of seed predation was significantly lower in outcrossed progeny than in inbred progeny. In contrast, inbreeding did not alter host plant quality and weevils developed in inbred and outcrossed plants had a similar biomass. Variations in fruit number were consistently associated with the infestation level in both experiments, whereas leaf size only predicted the number of weevils in one experiment, suggesting that fruit number is the most influential vigour-related characteristic of a weevil attack. These findings indicate that the costs of inbreeding of the interaction D. stramonium-T. soror were higher for inbred plants than for outcrossed plants. The interaction between seed predation and inbreeding depression could prevent the fixation of selfing as a unique reproductive strategy in D. stramonium.     

Plant chemistry underlies herbivore‐mediated inbreeding depression in nature

The cost of inbreeding (inbreeding depression, ID) is an important variable in the maintenance of reproductive variation. Ecological interactions such as herbivory could modulate this cost, provided that defence traits harbour deleterious mutations and herbivores are responsible for differences in fitness. In the field, we manipulated the presence of herbivores on experimentally inbred and outcrossed plants of Solanum carolinense (horsenettle) for three years. Damage was greater on inbred plants, and ID for growth and fitness was significantly greater under herbivory. Inbreeding reduced phenolic expression both qualitatively (phytochemical diversity) and quantitatively, indicating deleterious load at loci related to the biosynthesis of defence compounds. Our results indicate that inbreeding effects on plant–herbivore interactions are mediated by changes to functional plant metabolites, suggesting that variation in inbreeding could be a predictor of defence trait variation. The magnitude of herbivore‐mediated, ecological ID indicates that herbivores could maintain outcrossing mating systems in nature.     

The effect of inbreeding on defence against multiple enemies in Datura stramonium

The ability of plants to respond to natural enemies might depend on the availability of genetic variation for the optimal phenotypic expression of defence. Selfing can affect the distribution of genetic variability of plant fitness, resistance and tolerance to herbivores and pathogens. The hypothesis of inbreeding depression influencing plant defence predicts that inbreeding would reduce resistance and tolerance to damage by natural enemies relative to outcrossing. In a field experiment entailing experimentally produced inbred and outcrossed progenies, we assessed the effects of one generation of selfing on Datura stramonium resistance and tolerance to three types of natural enemies, herbivores, weevils and a virus. We also examined the effect of damage on relative growth rate (RGR), flower, fruit, and seed production in inbred and outcrossed plants. Inbreeding significantly reduced plant defence to natural enemies with an increase of 4% in herbivore damage and 8% in viral infection. These results indicate inbreeding depression in total resistance. Herbivory increased 10% inbreeding depression in seed number, but viral damage caused inbred and outcrossed plants to have similar seed production. Inbreeding and outcrossing effects on fitness components were highly variable among families, implying that different types or numbers of recessive deleterious alleles segregate following inbreeding in D. stramonium. Although inbreeding did not equally alter all the interactions, our findings indicate that inbreeding reduced plant defence to herbivores and pathogens in D. stramonium.     

Multigenerational effects of inbreeding in Cucurbita pepo ssp. texana (Cucurbitaceae)

The shape of the fitness function relating the decline in fitness with coefficient of inbreeding (f) can provide evidence concerning the genetic basis of inbreeding depression, but few studies have examined inbreeding depression across a range of f using noncultivated species. Futhermore, studies have rarely examined the effects of inbreeding depression in the maternal parent on offspring fitness. To estimate the shape of the fitness function, we examined the relationship between f and fitness across a range off from 0.000 to 0.875 for components of both male and female fitness in Cucurbita pepo ssp. texana. Each measure of female fitness declined with f, including pistillate flower number, fruit number, seed number per fruit, seed mass per fruit, and percentage seed germination. Several aspects of male fitness also declined with f, including staminate flower number, pollen number per flower, and the number of days of flowering, although cumulative inbreeding depression was less severe for male (0.34) than for female function (0.39). Fitness tended to decline linearly with f between f = 0.00 and f = 0.75 for most traits and across cumulative lifetime fitness (mean = 0.66), suggesting that individual genes causing inbreeding depression are additive and the result of many alleles of small effect. However, most traits also showed a small reduction in inbreeding depression between f = 0.75 and f = 0.875, and evidence of purging or diminishing epistasis was found for in vitro pollen-tube growth rate. To examine inbreeding depression as a maternal effect, we performed outcross pollinations on f = 0.0 and f = 0.5 mothers and found that depression due to maternal inbreeding was 0.07, compared to 0.10 for offspring produced through one generation of selfing. In at least some families, maternal inbreeding reduced fruit number, seed number and mass, staminate flower number, pollen diameter, and pollen-tube growth rate. Collectively these results suggest that, while the fitness function appears to be largely linear for most traits, maternal effects may compound the effects of inbreeding depression in multigenerational studies, though this may be partially offset by purging or diminishing epistasis.     

Inbreeding depression in <Emphasis Type="Italic">Solanum carolinense</Emphasis> (Solanaceae), a species with a plastic self-incompatibility response

Background  

Solanum carolinense (horsenettle) is a highly successful weed with a gametophytic self-incompatibility (SI) system. Previous studies reveal that the strength of SI in S. carolinense is a plastic trait, associated with particular S -alleles. The importance of this variation in self-fertility on the ability of horsenettle to found and establish new populations will depend, to a large extent, on the magnitude of inbreeding depression. We performed a series of greenhouse and field experiments to determine the magnitude of inbreeding depression in S. carolinense, whether inbreeding depression varies by family, and whether the estimates of inbreeding depression vary under field and greenhouse conditions. We performed a series of controlled self- and cross-pollinations on 16 genets collected from a large population in Pennsylvania to obtain progeny with different levels of inbreeding. We grew the selfed and outcrossed progeny in the greenhouse and under field conditions and recorded various measures of growth and reproductive output.     

Perspective: purging the genetic load: a review of the experimental evidence

Inbreeding depression, the reduction in fitness that accompanies inbreeding, is one of the most important topics of research in evolutionary and conservation genetics. In the recent literature, much attention has been paid to the possibility of purging the genetic load. If inbreeding depression is due to deleterious alleles, whose effect on fitness are negative when in a homozygous state, then successive generations of inbreeding may result in a rebound in fitness due to the selective decrease in frequency of deleterious alleles. Here we examine the experimental evidence for purging of the genetic load by collating empirical tests of rebounds in fitness-related traits with inbreeding in animals and plants. We gathered data from 28 studies including five mammal, three insect, one mollusc, and 13 plant species. We tested for purging by examining three measures of fitness-component variation with serial generations of inbreeding: (1) changes in inbreeding depression, (2) changes in fitness components of inbred lines relative to the original outbred line, and (3) purged population (outcrossed inbred lines) trait means as a function of ancestral outbred trait means. Frequent and substantial purging was found using all three measures, but was particularly pronounced when tracking changes in inbreeding depression. Despite this, we found little correspondence between the three measures of purging within individual studies, indicating that the manner in which a researcher chooses to estimate purging will affect interpretation of the results obtained. The discrepancy suggests an alternative hypothesis: rebounds in fitness with inbreeding may have resulted from adaptation to laboratory conditions and not to purging when using outcrossed inbred lines. However, the pronounced reduction in inbreeding depression for a number of studies provides evidence for purging, as the measure is likely less affected by selection for laboratory conditions. Unlike other taxon-specific reviews on this topic, our results provide support for the purging hypothesis, but firm predictions about the situations in which purging is likely or the magnitude of fitness rebound possible when populations are inbred remain difficult. Further research is required to resolve the discrepancy between the results obtained using different experimental approaches.     

INBREEDING DEPRESSION IN HYDROPHYLLUM APPENDICULATUM: ROLE OF MATERNAL EFFECTS,CROWDING, AND PARENTAL MATING HISTORY

This paper examines several aspects of the expression of inbreeding depression in an outcrossing, obligately biennial plant, Hydrophyllum appendiculatum (Hydrophyllaceae). The amount of inbreeding depression detected was small during the first year of life but increased with age and had significant effects on adult size and reproductive traits. The lack of significant inbreeding depression during early growth is likely due to the overriding influence of maternal environmental effects on seed size and seedling growth. However, as maternal effects decreased with age, the seedling's own genotype became a more important determinant of its fate. To examine whether the expression of inbreeding depression was sensitive to ecological conditions, selfed and outcrossed seedlings were grown alone or with other H. appendiculatum seedlings. No inbreeding depression was detected in the plants grown alone. In contrast, under competitive conditions, outcrossed seedlings were significantly larger than selfed seedlings by the end of the first growing season. To address whether parental mating history influences the amount of inbreeding depression expressed, I examined the consequences of two successive generations of selfing on seed set and seed weight. The amount of inbreeding depression increased following the second generation of selfing. In the first generation, seed set and seed weight differed by less than 5% between selfed and outcrossed progeny. However, both traits were 15% greater for outcrossed plants after two generations. These results indicate that the alleles responsible for the reductions in these traits were not purged and suggest the action of multiple loci with deleterious effects.     

MEASURES OF PHENOTYPIC SELECTION ARE BIASED BY PARTIAL INBREEDING

When populations are partially inbred due to the population structure or to a mixed mating system like partial self-fertilization, some individuals will be more inbred than others. This heterogeneity among individuals in the history of inbreeding can greatly complicate the interpretation of measures of quantitative genetic variability when the traits studied exhibit inbreeding depression. Partial inbreeding can also bias measures of phenotypic selection toward the detection of strong directional and stabilizing selection. In this paper, data are presented from several inbreeding experiments conducted on two partially selfing, annual populations of the monkeyflower Mimulus guttatus that show that the means of many of the morphological and phenological traits measured were affected by inbreeding. These findings imply that estimates of heritabilities and additive genetic covariances would not reflect the potential for these populations to respond to selection. Phenotypic selection analyses conducted on naturally occurring plants, involving linear regressions of relative seed production on the traits, revealed significant directional selection on many of the same quantitative traits measured in the inbreeding studies. However, when the same selection analyses were performed on plants with known histories of inbreeding, part of the statistical relationship between relative seed number and the traits was found to be due to the mating system: inbred individuals had both lower seed production and different mean values for the traits than outcrossed individuals. It is also shown, with a hypothetical example, that partial inbreeding can bias measures of stabilizing selection toward the detection of strong stabilizing selection. Partial inbreeding therefore tends to make directional and stabilizing selection appear stronger than it is, and it may be that natural selection in the wild is actually weaker than many studies of partially inbred species suggest.     

Outcrossing rate and inbreeding depression in the herbaceous autotetraploid,Campanula americana

Polyploidy in angiosperms is frequently associated with an increase in self-compatibility. Self-fertilization can enhance polyploid establishment, and theory predicts reduced inbreeding depression in polyploids relative to diploids. Therefore, we may expect mating systems that promote self-fertilization or mixed-mating in polyploid species. However, few studies have measured polyploid mating systems and inbreeding depression. We report the outcrossing rate and inbreeding depression for Campanula americana, a self-compatible protandrous herb. Allozyme genotypes suggest that C. americana is an autotetraploid with tetrasomic inheritance. We found that the multilocus outcrossing rate, t(m)=0.938, did not differ from unity. This result was unexpected since previous work demonstrated that pollinators frequently move from male- to female-phase flowers on the same plant, that is, geitonogamy. Self and outcross pollinations were conducted for three populations. Offspring were germinated in controlled conditions and grown to maturity in pots in nature. Inbreeding depression was not significant for most seed and germination characters. However, all later life traits except flowering date differed between inbred and outcrossed individuals resulting in a 26% reduction in cumulative fitness for inbred plants. Limited early- and moderate later-life inbreeding depression suggest that it is buffered by the higher levels of heterozygosity found in an autotetraploid. C. americana appears to have a flexible mating system where within flower protandry and/or cryptic self-incompatibility result in a high outcrossing rate when pollinators are abundant, but self-compatibility and limited inbreeding depression maintain reproductive success when mates are limited.     

THE EFFECT OF DISTANCE FROM THE PARENTAL SITE ON OFFSPRING PERFORMANCE AND INBREEDING DEPRESSION IN IMPATIENS CAPENSIS: A TEST OF THE LOCAL ADAPTATION HYPOTHESIS

If microgeographic variation in selection within a natural plant population has resulted in local adaptation, then offspring fitness should decline with distance from the parental site. If outcrossed progeny are less well-adapted to the parental environment than inbred progeny, but perform better in environments different from that of the parent, then the fitness of inbred progeny relative to outcrossed progeny should decrease with dispersal distance from the parent. To test these predictions, we collected seedlings at 10-m intervals from a 40 times 40-m permanent grid in a natural population of Impatiens capensis, grew them in a greenhouse, and crossed them to produce outcrossed chasmogamous seeds. Seedlings from outcrossed chasmogamous and self-fertilized cleistogamous seeds were planted back into the source population in the original site of their maternal parents and in arcs 3 and 12 m from the parental location and censused weekly for survival and reproduction. The fitness of inbred offspring declined significantly and the magnitude of observed inbreeding depression increased with distance from the parental site, supporting the local adaptation hypothesis.     

INBREEDING DEPRESSION IN MORPHOLOGICAL AND PHYSIOLOGICAL TRAITS OF SCHIEDEA LYDGATEI (CARYOPHYLLACEAE) IN TWO ENVIRONMENTS

We compared inbreeding depression in hermaphroditic Schiedea lydgatei and its gynodioecious sister species, S. salicaria, to infer the level of inbreeding depression in their common ancestor. With measurements of selfing rates, this information can be used to assess the importance of inbreeding depression in the evolution of breeding systems in S. lydgatei and S. salicaria. Morphological and physiological characters related to fitness were compared for inbred and outcrossed S. lydgatei in high- and low-fertilizer environments in the greenhouse. Seed mass, number of seeds per capsule, germination, survival, biomass, number of flowers, and age at first flowering were compared for inbred versus outcrossed progeny. We also measured inbreeding depression in maximal rates of photosynthetic carbon assimilation and stomatal conductance to water vapor, traits that affect fitness through their influence on plant carbon balance and water-use efficiency (ratio of carbon gain to water loss). All traits except number of seeds per capsule in parents and survival showed inbreeding depression, with the magnitude depending on family and environment. High inbreeding depression is likely in the ancestor of S. lydgatei and S. salicaria, indicating that, with sufficiently high selfing rates, females could spread in populations. Hermaphroditism in S. lydgatei is probably favored by low selfing rates. In contrast, the evolution of gynodioecy in S. salicaria apparently has been favored by relatively high selfing rates in combination with high inbreeding depression.     

Fitness Traits and Dispersal Ability in the Herb Tragopogon pratensis (Asteraceae): Decoupling the Role of Inbreeding Depression and Maternal Effects

Abstract: Inbreeding depression can decrease several fitness traits and maternal effects can strongly influence the amount of inbreeding depression. Understanding the effects of inbreeding depression on plant fitness is especially important in the context of habitat fragmentation, where plant populations become smaller and more isolated, exhibiting increasing levels of inbreeding depression. We examined the joint influence of inbreeding depression and maternal effects on life cycle traits and dispersal ability in the herb Tragopogon pratensis that grows in fragmented populations in Europe. We conducted experimental crosses to obtain selfed and outcrossed progeny in two contrasted environments. In particular, we produced a first generation of seeds and plants that were self-pollinated again to produce a second generation of seeds. Individual seeds were weighed and their pappuses measured to estimate the dispersal potential. Pollination treatment only had a significant effect on seed mass and dispersal ability. Coefficients of inbreeding depression did not differ between selfed and outcrossed plants. Seed mass had a significant effect on germination date. Environment had a significant effect on mass of the second generation of seeds and the interaction between pollination treatment and family was significant for six traits, indicating the existence of strong maternal effects in T. pratensis. Results suggest population differentiation. Overall, T. pratensis populations exhibited a good performance under selfing, in terms of life cycle traits and dispersal ability, which would allow the species to cope with problems associated with fragmentation.     

EVOLUTION OF GYNODIOECY AND MAINTENANCE OF FEMALES: THE ROLE OF INBREEDING DEPRESSION,OUTCROSSING RATES,AND RESOURCE ALLOCATION IN SCHIEDEA ADAMANTIS (CARYOPHYLLACEAE)

Levels of inbreeding depression, outcrossing rates, and phenotypic patterns of resource allocation were studied to examine their relative importance in the maintenance of high numbers of females in gynodioecious Schiedea adamantis (Caryophyllaceae), an endemic Hawaiian shrub found in a single population on Diamond Head Crater, Oahu. In studies of inbreeding depression in two greenhouse environments, families of hermaphrodites exhibited significant inbreeding depression (δ = 0.60), based on a multiplicative fitness function using seeds per capsule, germination, survival, and the inflorescence biomass of progeny. Differences between inbred and outcrossed progeny were smallest at the early stage of seeds per capsule and more pronounced at the later stages of survival and inflorescence production. These results are consistent with inbreeding depression caused by many mutations of small effect. Using allozyme analyses, the inbreeding coefficient of adult plants in the field was not significantly different from zero, implying that δ in nature may be equal to one. The single locus estimate of the outcrossing rate for hermaphrodites was 0.50 based on progeny that survived to flowering; corrected for the disproportionate loss before flowering of progeny from selfing, the adjusted outcrossing rate at the zygote stage was 0.32, suggesting that considerable selfing occurs in hermaphrodites. Females were totally outcrossed. When females and hermaphrodites were compared for reproductive output in the field, females produced over twice as many seeds per plant as hermaphrodites, primarily because females had far more capsules per inflorescence than hermaphrodites. Females had greater mass per seed than hermaphrodites in the field, either because of greater provisioning or reduced inbreeding depression. There was no significant differential mortality with respect to sex over a seven year period. The higher number of seeds per plant of females, combined with substantial inbreeding depression and relatively high selfing rates for hermaphrodites, are probably responsible for the maintenance of females in this population. The predicted frequency of females based on data for seed production, the adjusted selfing rate, and inbreeding depression is 42%, remarkably close to the observed frequency of 39%. High levels of inbreeding depression suggest that considerable quantitative genetic variation is present for traits affecting fitness in this population, despite low allozyme variability and a presumed founder effect.     

Early inbreeding depression in the sexually polymorphic plant Dianthus sylvestris (Caryophyllaceae): Effects of selfing and biparental inbreeding among sex morphs

Predominantly outcrossing plant species are expected to accumulate recessive deleterious mutations, which can be purged when in a homozygous state following selfing. Individuals may vary in their genetic load because of different selfing histories, which could lead to differences in inbreeding depression among families. Lineage-dependent inbreeding depression can appear in gynodioecious species if obligatory outcrossed females are more likely to produce female offspring and if partially selfing hermaphrodites are more likely to produce hermaphrodites. We investigated inbreeding depression at the zygote, seed, and germination stages in the gynomonoecious-gynodioecious Dianthus sylvestris, including pure-sexed plants and a mixed morph. We performed hand-pollinations on 56 plants, belonging to the three morphs, each receiving 2-3 cross treatments (out-, sib- and self-pollination) on multiple flowers. Effects of cross treatments varied among stages and influenced seed provisioning, with sibling competition mainly occurring within outcrossed fruits. We found significant inbreeding depression for seed mass and germination and cumulative early inbreeding depression varied greatly among families. Among sex morphs, we found that females and hermaphrodites differed in biparental inbreeding depression, whereas uniparental was similar for all. Significant inbreeding depression levels may play a role in female maintenance in this species, and individual variation in association with sex-lineages proclivity is discussed.     

ENHANCEMENT OF INBREEDING DEPRESSION BY DOMINANCE AND SUPPRESSION IN IMPATIENS CAPENSIS

We investigated the effect of intraspecific competition on the magnitude of inbreeding depression in Impatiens capensis by planting seeds from chasmogamous (CH) and cleistogamous (CL) flowers in three experimental greenhouse treatments: in individual pots, in flats in dense pure stands according to seed type, and in flats with the two seed types intermixed in a checkerboard array. The size distributions of plants grown in flats were significantly more hierarchical than those of plants grown individually, indicating that larger plants competitively suppressed smaller plants in the high-density treatments. The magnitude of inbreeding depression at high density depended upon the planting arrangement of CL and CH seeds. CH advantage was greatest when CH and CL seedlings were grown in competition with one another, suggesting that fitness differences between outcrossed and inbred individuals were intensified by dominance and suppression. For plants grown individually, the effects of maternal parent, seed weight, and emergence date on seedling size disappeared with plant age, whereas at high density these effects remained at the final harvest. Thus, plant density may influence patterns of natural selection both on mating system and on juvenile traits in natural Impatiens populations.