Inbreeding depression and selfing rates in a self-compatible,hermaphroditic species,Schiedea membranacea (Caryophyllaceae)

Inbreeding depression and selfing rates were investigated in Schiedea membranacea (Caryophyllaceae), a hermaphroditic species endemic to the Hawaiian Islands. Most theoretical models predict high inbreeding depression in outcrossing hermaphroditic species and low inbreeding depression in inbreeding species. Although high outcrossing rates and high levels of inbreeding depression are characteristic of many species of Schiedea, self- fertilization is common among relatives of hermaphroditic S. membranacea, and high selfing rates and low levels of inbreeding depression were predicted in this species. Sixteen individuals grown in the greenhouse were used to produce selfed and outcrossed progeny. Inbreeding depression, which was evident throughout the stages measured (percentage viable seeds per capsule, mean seed mass, percentage seed germination, percentage seedling survival, and biomass after 8 mo), averaged 0.70. Inbreeding depression among maternal families varied significantly for all measured traits and ranged from −0.12 to 0.97. Using isozyme analysis, the multilocus selfing rate varied from 0.13 to 0.38 over 4 yr. Contrary to the initial prediction of high selfing and low inbreeding depression based on phylogenetic relationships within Schiedea, low selfing rates and high levels of inbreeding depression were found in S. membranacea. These results indicate that outcrossing is stable in this species and maintained by high levels of inbreeding depression.     

OUTCROSSING RATE AND INBREEDING DEPRESSION IN TWO ANNUAL MONOECIOUS HERBS,BEGONIA HIRSUTA AND B. SEMIOVATA

Most models of mating-system evolution predict inbreeding depression to be low in inbred populations due to the purging of deleterious recessive alleles. This paper presents estimates of outcrossing rates and inbreeding depression for two highly selfing, monoecious annuals Begonia hirsuta and B. semiovata. Outcrossing rates were estimated using isozyme polymorphisms, and the magnitude of inbreeding depression was quantified by growing progeny in the greenhouse produced through controlled selfing and outcrossing. The estimated single-locus outcrossing rate was 0.03 ± 0.01 (SE) for B. hirsuta and 0.05 ± 0.02 for B. semiovata. In both species, the seed production of selfed flowers was on average 12% lower than that of outcrossed flowers (B. hirsuta P = 0.07, B. semiovata P < 0.05, mixed model ANOVAs). There was no significant effect of crosstype on germination rate or survival, but selfed offspring had a lower dry mass than outcrossed offspring 18 weeks after planting in both species (on average 18% lower in B. hirsuta and 31% lower in B. semiovata). Plants that were the products of selfing began flowering later than plants produced through outcrossing in B. semiovata, but not in B. hirsuta. The effects of crosstype on seed production (B. semiovata), days to first flower and offspring dry mass (both species) varied among maternal parents, as indicated by significant crosstype x maternal parent interactions for these characters. Both species showed significant inbreeding depression for total fitness (estimated as the product of seed production, germination rate, survival and dry mass at 18 weeks). In B. hirsuta, the average total inbreeding depression was 22% (range -57%-98%; N = 23 maternal parents), and in B. semiovata, it was 42% (-11%-84%; N = 21). This study demonstrates that highly selfing populations can harbor substantial inbreeding depression. Our findings are consistent with the hypothesis that a high mutation rate to mildly deleterious alleles contributes to the maintenance of inbreeding depression in selfing populations.     

No inbreeding depression in an outcrossing alpine species: The breeding system of Campanula thyrsoides

Plants that live in fragmented landscapes, where populations are isolated from each other and in which long-distance dispersal is essential for colonization of empty sites, reproduction should be favoured by self-compatibility (Baker's law). Nevertheless, outcrossing mechanisms, such as self-incompatibility and dichogamy, are common in many species and are often maintained by inbreeding depression in the fitness of selfed progeny. Here, we studied the breeding system and the consequences of selfing and sister mating in Campanula thyrsoides, a short-lived perennial monocarp, which is found in the naturally fragmented landscape of the Alps. An experiment with controlled pollinations was set up in the common garden with plants grown from seeds originating from 14 seed families, collected in the siliceous Central Alps, where this plant is found on isolated carbonate bearing outcrops.Our results indicate that C. thyrsoides has a strong self-incompatibility system (SI) with no or low seed set in selfed flowers compared to outcrossed and sister-crossed flowers. Moreover, the SI system in C. thyrsoides did not break down with flower age as in some other Campanula species. Surprisingly, there was no significant difference in seed set, seed weight, germination percentage, seedling survival and size between outcrossed and sister-crossed offspring, which indicates no inbreeding depression.We suggest that the absence of inbreeding depression in this outcrossing species might be a result of frequent bottlenecks during colonization of the isolated habitats in the alpine landscape.     

Selfing and inbreeding depression in seeds and seedlings of Neobalanocarpus heimii (Dipterocarpaceae)

We evaluated the degree of selfing and inbreeding depression at the seed and seedling stages of a threatened tropical canopy tree, Neobalanocarpus heimii, using microsatellite markers. Selection resulted in an overall decrease in the level of surviving selfed progeny from seeds to established seedlings, indicating inbreeding depression during seedling establishment. Mean seed mass of selfed progeny was lower than that of outcrossed progeny. Since the smaller seeds suffered a fitness disadvantage at germination in N. heimii, the reduced seed mass of selfed progeny would be one of the determinants of the observed inbreeding depression during seedling establishment. High selfing rates in some mother trees could be attributed to low local densities of reproductive individuals, thus maintenance of a sufficiently high density of mature N. heimii should facilitate regeneration and conservation of the species.     

Relatively weak inbreeding depression in selfing but also in outcrossing populations of North American Arabidopsis lyrata

Hermaphroditic plants can potentially self‐fertilize, but most possess adaptations that promote outcrossing. However, evolutionary transitions to higher selfing rates are frequent. Selfing comes with a transmission advantage over outcrossing, but self‐progeny may suffer from inbreeding depression, which forms the main barrier to the evolution of higher selfing rates. Here, we assessed inbreeding depression in the North American herb Arabidopsis lyrata, which is normally self‐incompatible, with a low frequency of self‐compatible plants. However, a few populations have become fixed for self‐compatibility and have high selfing rates. Under greenhouse conditions, we estimated mean inbreeding depression per seed (based on cumulative vegetative performance calculated as the product of germination, survival and aboveground biomass) to be 0.34 for six outcrossing populations, and 0.26 for five selfing populations. Exposing plants to drought and inducing defences with jasmonic acid did not magnify these estimates. For outcrossing populations, however, inbreeding depression per seed may underestimate true levels of inbreeding depression, because self‐incompatible plants showed strong reductions in seed set after (enforced) selfing. Inbreeding‐depression estimates incorporating seed set averaged 0.63 for outcrossing populations (compared to 0.30 for selfing populations). However, this is likely an overestimate because exposing plants to 5% CO₂ to circumvent self‐incompatibility to produce selfed seed might leave residual effects of self‐incompatibility that contribute to reduced seed set. Nevertheless, our estimates of inbreeding depression were clearly lower than previous estimates based on the same performance traits in outcrossing European populations of A. lyrata, which may help explain why selfing could evolve in North American A. lyrata.     

Outcrossing rate and inbreeding depression in the perennial yellow bush lupine, Lupinus arboreus (Fabaceae)

Little is known about the breeding systems of perennial Lupinus species. We provide information about the breeding system of the perennial yellow bush lupine, Lupinus arboreus, specifically determining self-compatibility, outcrossing rate, and level of inbreeding depression. Flowers are self-compatible, but autonomous self-fertilization rarely occurs; thus selfed seed are a product of facilitated selfing. Based on four isozyme loci from 34 maternal progeny arrays of seeds we estimated an outcrossing rate of 0.78. However, when we accounted for differential maturation of selfed seeds, the outcrossing rate at fertilization was lower, ～0.64. Fitness and inbreeding depression of 11 selfed and outcrossed families were measured at four stages: seed maturation, seedling emergence, seedling survivorship, and growth at 12 wk. Cumulative inbreeding depression across all four life stages averaged 0.59, although variation existed between families for the magnitude of inbreeding depression. Inbreeding depression was not manifest uniformly across all four life stages. Outcrossed flowers produced twice as many seeds as selfed flowers, but the mean performance of selfed and outcrossed progeny was not different for emergence, seedling survivorship, and size at 12 wk. Counter to assumptions about this species, L. arboreus is both self-compatible and outcrosses ～78% of the time.     

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.     

Experimental and genetic analyses reveal that inbreeding depression declines with increased self‐fertilization among populations of a coastal dune plant

Theory predicts that inbreeding depression (ID) should decline via purging in self‐fertilizing populations. Yet, intraspecific comparisons between selfing and outcrossing populations are few and provide only mixed support for this key evolutionary process. We estimated ID for large‐flowered (LF), predominantly outcrossing vs. small‐flowered (SF), predominantly selfing populations of the dune endemic Camissoniopsis cheiranthifolia by comparing selfed and crossed progeny in glasshouse environments differing in soil moisture, and by comparing allozyme‐based estimates of the proportion of seeds selfed and inbreeding coefficient of mature plants. Based on lifetime measures of dry mass and flower production, ID was stronger in nine LF populations [mean δ = 1?(fitness of selfed seed/fitness of outcrossed seed) = 0.39] than 16 SF populations (mean δ = 0.03). However, predispersal ID during seed maturation was not stronger for LF populations, and ID was not more pronounced under simulated drought, a pervasive stress in sand dune habitat. Genetic estimates of δ were also higher for four LF (δ = 1.23) than five SF (δ = 0.66) populations; however, broad confidence intervals around these estimates overlapped. These results are consistent with purging, but selective interference among loci may be required to maintain strong ID in partially selfing LF populations, and trade‐offs between selfed and outcrossed fitness are likely required to maintain outcrossing in SF populations.     

INBREEDING DEPRESSION IN GYNODIOECIOUS LOBELIA SIPHILITICA: AMONG-FAMILY DIFFERENCES OVERRIDE BETWEEN-MORPH DIFFERENCES

If inbreeding depression is caused by deleterious recessive alleles, as suggested by the partial dominance hypothesis, a negative correlation between inbreeding and inbreeding depression is predicted. This hypothesis has been tested several times by comparisons of closely related species or comparisons of populations of the same species with different histories of inbreeding. However, if one is interested in whether this relationship contributes to mating-system evolution, which occurs within populations, comparisons among families within a population are needed; that is, inbreeding depression among individuals with genetically based differences in their rate of selfing should be compared. In gynodioecious species with self-compatible hermaphrodites, hermaphrodites will have a greater history of potential inbreeding via both selfing and biparental inbreeding as compared to females and may therefore express a lower level of inbreeding depression. We estimated the inbreeding depression of female and hermaphrodite lineages in gynodioecious Lobelia siphilitica in a greenhouse experiment by comparing the performance of selfed and outcrossed progeny, as well as sibling crosses and crosses among subpopulations. We did not find support for lower inbreeding depression in hermaphrodite lineages. Multiplicative inbreeding depression (based on seed germination, juvenile survival, survival to flowering, and flower production in the first growing season) was not significantly different between hermaphrodite lineages (δ = 0.30 ± 0.08) and female lineages (δ = 0.15 ± 0.18), although the trend was for higher inbreeding depression in the hermaphrodite lineages. The population-level estimate of inbreeding depression was relatively low for a gynodioecious species (δ = 0.25) and there was no significant inbreeding depression following biparental inbreeding (δ = 0.01). All measured traits showed significant variation among families, and there was a significant interaction between family and pollination treatment for four traits (germination date, date of first flowering, number of flowers, and aboveground biomass). Our results suggest that the families responded differently to selfing and outcrossing: Some families exhibited lower fitness following selfing whereas others seemed to benefit from selfing as compared to outcrossing. Our results support recent simulation results in that prior inbreeding of the lineages did not determine the level of inbreeding depression. These results also emphasize the importance of determining family-level estimates of inbreeding depression, relative to population-level estimates, for studies of mating-system evolution.     

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.     

EVOLUTION OF THE MAGNITUDE AND TIMING OF INBREEDING DEPRESSION IN PLANTS

Estimates of inbreeding depression obtained from the literature were used to evaluate the association between inbreeding depression and the degree of self-fertilization in natural plant populations. Theoretical models predict that the magnitude of inbreeding depression will decrease with inbreeding as deleterious recessive alleles are expressed and purged through selection. If selection acts differentially among life history stages and deleterious effects are uncorrelated among stages, then the timing of inbreeding depression may also evolve with inbreeding. Estimates of cumulative inbreeding depression and stage-specific inbreeding depression (four stages: seed production of parent, germination, juvenile survival, and growth/reproduction) were compiled for 79 populations (using means of replicates, N = 62) comprising 54 species from 23 families of vascular plants. Where available, data on the mating system also were collected and used as a measure of inbreeding history. A significant negative correlation was found between cumulative inbreeding depression and the primary selfing rate for the combined sample of angiosperms (N = 35) and gymnosperms (N = 9); the correlation was significant for angiosperms but not gymnosperms examined separately. The average inbreeding depression in predominantly selfing species (δ = 0.23) was significantly less (43%) than that in predominantly outcrossing species (δ = 0.53). These results support the theoretical prediction that selfing reduces the magnitude of inbreeding depression. Most self-fertilizing species expressed the majority of their inbreeding depression late in the life cycle, at the stage of growth/reproduction (14 of 18 species), whereas outcrossing species expressed much of their inbreeding depression either early, at seed production (17 of 40 species), or late (19 species). For species with four life stages examined, selfing and outcrossing species differed in the magnitude of inbreeding depression at the stage of seed production (selfing δ = 0.05, N = 11; outcrossing δ = 0.32, N = 31), germination (selfing δ = 0.02, outcrossing δ = 0.12), and survival to reproduction (selfing δ = 0.04, outcrossing δ = 0.15), but not at growth and reproduction (selfing δ = 0.21, outcrossing δ = 0.27); inbreeding depression in selfers relative to outcrossers increased from early to late life stages. These results support the hypothesis that most early acting inbreeding depression is due to recessive lethals and can be purged through inbreeding, whereas much of the late-acting inbreeding depression is due to weakly deleterious mutations and is very difficult to purge, even under extreme inbreeding.     

LIMITS TO REPRODUCTIVE SUCCESS IN A PARTIALLY SELF-INCOMPATIBLE HERB: FECUNDITY DEPRESSION AT SERIAL LIFE-CYCLE STAGES

Like many angiosperms, Crinum erubescens is partially self-compatible, producing fewer seeds upon selfing than after outcrossing. In this paper we test the relative magnitude of the prefertilization and postfertilization effects of self-incompatibility, inbreeding depression, or both in a natural population of this hermaphroditic tropical herb. We characterize prefertilization effects by examining pollen tube growth, while postfertilization effects are characterized by examination of embryo abortion and seed maturation. Statistical methods are developed to test the magnitude of these effects from one life-cycle stage to the next. We find that although pollen performance in selfed flowers is lower than that in outcrossed flowers, pollen performance is low overall. Postfertilization effects attributable to inbreeding depression account for a larger proportion of the reduction in fecundity in selfed compared to outcrossed flowers. Among naturally pollinated plants, despite ample pollen deposition, the numbers of fruits and seeds set are intermediate to selfed and outcrossed treatments.     

INBREEDING DEPRESSION IN SCHIEDEA GLOBOSA AND S. SALICARIA (CARYOPHYLLACEAE), SUBDIOECIOUS AND GYNODIOECIOUS HAWAIIAN SPECIES

Progeny produced by inbreeding were compared to progeny derived from outcrosses for gynodioecious Schiedea salicaria and subdioecious S. globosa to assess fitness consequences of breeding system on parental fecundity (seeds per capsule) and progeny measures of fitness (germination, survival, biomass, and number of flowers). Results from both species indicated that inbreeding depression occurred at all measured stages of the life history. In both species, different females showed different levels of inbreeding depression. Multiplicative fitness functions of the ratio of values for selfed and outcrossed progeny in S. salicaria resulted in inbreeding depression values of 0.62–0.94. Within- vs. between-family crosses of S. globosa also resulted in inbreeding depression values as high as 0.49. These values suggest that inbreeding depression may promote the evolution of dioecy within S. globosa and S. salicaria, depending on the levels of natural outcrossing.     

Evolution of the Selfing Rate and Resource Allocation Models

Abstract First, evolutionary theories of selfing of terrestrial plants are reviewed briefly. The evolution of the selfing rate is controlled mainly by (1) the benefit of enhanced genetic relatedness to seeds and (2) the cost of lowered fitness of selfed offspring (inbreeding depression), being modified by (3) fertility assurance under pollen limitation, (4) reduced performance as pollen donor, (5) reduced expenditure to male function, and (6) lowered genetic recombination. Models of the joint evolution of selfing and inbreeding depression predict either strong outcrossing or predominant selfing. Although wind-pollinated plants fit the prediction, some animal-pollinated species have intermediate selfing rates, refuting the theory.
Second, three resource allocation models are analyzed, in which an individual plant optimally allocates limited resources to outcrossed seeds, selfed seeds, and to energy reserves for the next year. The first model explains how the number of outcrossed and selfed offspring change with plant size when they differ in dispersal distance. The second model predicts that, in a disturbed habitat, the plant is likely to be annual and to produce both selfed and outcrossed seeds; in contrast, in a stable habitat, the plant tends to be perennial and to abort selfed seeds selectively. Hand pollination may increase seed production for perennials but not for annuals. The third model explains the observed difference between animal and wind pollinated plants in the out-crossing rate pattern by the difference in the way pollen acquisition increases with investment.     

Joint evolution of differential seed dispersal and self‐fertilization

Differential seed dispersal, in which selfed and outcrossed seeds possess different dispersal propensities, represents a potentially important individual‐level association. A variety of traits can mediate differential seed dispersal, including inflorescence and seed size variation. However, how natural selection shapes such associations is poorly known. Here, we developed theoretical models for the evolution of mating system and differential seed dispersal in metapopulations, incorporating heterogeneous pollination, dispersal cost, cost of outcrossing and environment‐dependent inbreeding depression. We considered three models. In the ‘fixed dispersal model’, only selfing rate is allowed to evolve. In the ‘fixed selfing model’, in which selfing is fixed but differential seed dispersal can evolve, we showed that natural selection favours a higher, equal or lower dispersal rate for selfed seeds to that for outcrossed seeds. However, in the ‘joint evolution model’, in which selfing and dispersal can evolve together, evolution necessarily leads to higher or equal dispersal rate for selfed seeds compared to that for outcrossed. Further comparison revealed that outcrossed seed dispersal is selected against by the evolution of mixed mating or selfing, whereas the evolution of selfed seed dispersal undergoes independent processes. We discuss the adaptive significance and constraints for mating system/dispersal association.     

The cost of selfing inEncyclia cochleata (Orchidaceae)

To determine whether inbreeding depression accounts for the maintenance of outcrossing in populations of the self-compatible orchidEncyclia cochleata, the estimated selective advantage of selfing was compared to a measure of inbreeding depression. Individuals from three populations ofE. cochleata and some of their progeny were phenotyped using isozyme analysis. The electrophoretic data were used to estimate the outcrossing rate and the theoretical cost of outcrossing. Inbreeding depression was estimated by comparing the fitness of the progeny resulting from both types of pollinations. The seeds from outcrossed and selfed hand-pollinations and naturally pollinated seeds from a population of the triandrous form ofE. cochleata were grown aseptically on culture media, and their development over the next three years recorded. Inbreeding was common, particularly in one population (outcrossing rate 40%). However, the level of inbreeding depression was only 1–2%, considerably less inbreeding depression than expected.     

Inbreeding depression and mixed mating in Leptosiphon jepsonii: a comparison of three populations

BACKGROUND AND AIMS: Inbreeding depression is thought to play a central role in the evolution and maintenance of cross-fertilization. Theory indicates that inbreeding depression can be purged with self-fertilization, resulting in positive feedback for the selection of selfing. Variation among populations of Leptosiphon jepsonii in the timing and rate of self-fertilization provides an opportunity to study the evolution of inbreeding depression and mating systems. In addition, the hypothesis that differences in inbreeding depression for male and female fitness can stabilize mixed mating in L. jepsonii is tested. METHODS: In a growth room experiment, inbreeding depression was measured in three populations with mean outcrossing rates ranging from 0.06 to 0.69. The performance of selfed and outcrossed progeny is compared at five life history stages. To distinguish between self-incompatibility and early inbreeding depression, aborted seeds and unfertilized ovules were counted in selfed and outcrossed fruits. In one population, pollen and ovule production was quantified to estimate inbreeding depression for male and female fitness. KEY RESULTS: Both prezygotic barriers and inbreeding depression limited self seed set in the most outcrossing population. Cumulative inbreeding depression ranged from 0.297 to 0.501, with the lowest value found in the most selfing population. Significant inbreeding depression for early life stages was found only in the more outcrossing populations. Inbreeding depression was not significant for pollen or ovule production. CONCLUSIONS: The results provide modest support for the hypothesized relationship between inbreeding depression and mating systems. The absence of early inbreeding depression in the more selfing populations is consistent with theory on purging. Differences in male and female expression of inbreeding depression do not appear to stabilize mixed mating in L. jepsonii. The current estimates of inbreeding depression for L. jepsonii differ from those of previous studies, underscoring the effects of environmental variation on its expression.     

Self-pollination and its costs in a monoecious fig (Ficus aurea, Moraceae) in a highly seasonal subtropical environment

The unusual floral phenology of most monoecious figs, related to their highly specialized pollination mutualism with agaonid wasps, combines pronounced dichogamy at the level of inflorescences and individuals with population-level asynchrony in flowering. This floral phenology ensures that outcrossing strongly predominates. Fig populations may thus be expected to possess deleterious recessive alleles that lead to inbreeding depression when selfing does occur. However, whether monoecious figs are self-compatible and whether selfing results in inbreeding depression have never been investigated. Using wasps as "pollination tools" and exploiting infrequent overlap in male and female phases on the same tree, we conducted controlled selfed and outcrossed pollination experiments in Ficus aurea. Our results show that this species is totally self-compatible. No negative effects of selfing could be demonstrated on syconium retention, number of vacant ovaries, seed set, or seed germination. However, wasp production had a tendency to be higher after self-pollination. While it is possible that inbreeding depression is expressed at later developmental stages, its absence at the early stages we examined is nonetheless surprising for a plant expected to be highly outcrossed. It is likely that selection pressures other than avoidance of inbreeding are responsible for the evolution and maintenance of the unusual floral phenology of figs.     

RELATIVE FITNESS OF SELFED AND OUTCROSSED PROGENY IN A SELF-COMPATIBLE,PROTANDROUS SPECIES,SABATIA ANGULARIS L. (GENTIANACEAE): A COMPARISON IN THREE ENVIRONMENTS

The consequences of selfing were examined for a population of self-compatible, protandrous, Sabatia angularis L. (Gentianaceae). Field-collected plants were hand-pollinated in the greenhouse to produce selfed progeny and outcrossed progeny from parents separated by a maximum of 5 m (near-outcross) and 85 m (far-outcross) in the field. Self, near-outcross, and far-outcross half sib progeny were grown in the greenhouse, a garden plot, and their native habitat. Progeny were compared by multiplicative fitness functions based on seed production per hand-pollination, seed germination, rosette formation, survival to reproduction, and reproduction in each environment. Variation in reproduction among progeny groups was influenced by the environment in which they were grown. Significant inbreeding depression was detected between the self and far-outcross progeny in each environment. Only the natural environment demonstrated a greater than 50% reduction in relative fitness of self compared to near-outcross progeny. This is of biological relevance since near-outcross hand-pollinations occurred within the range of pollen and seed dispersal suggesting that inbreeding depression in S. angularis is strong enough to maintain outcrossing in the study population. In the field, the far-outcross progeny outperformed the near-outcross progeny suggesting local population substructure. The magnitude of the inbreeding depression expressed among the self progeny was the greatest in the field, intermediate in the garden plot, and the least in the greenhouse.     

Effects of cleistogamy and pollen source on seed production and offspring performance in three endangered violets

In rare plants that often occur in small or isolated populations the probability of selfing between close relatives is increased as a consequence of demographic stochasticity. The mode of pollination (selfing, outcrossing) may have considerable effects on seed traits and offspring performance and hence potential viability. Since current efforts aiming at the restoration of floodplain grasslands through the transfer of plant material from species-rich source stands may lead to the establishment of initially small populations consisting of founders from different populations, the present paper experimentally investigated the effects of pollen source and floral types (i.e. chasmogamous (CH) and cleistogamous (CL) flowers) on seed traits and offspring performance in three highly endangered violet species (Viola elatior, V. pumila, V. stagnina) of these grasslands. We estimated inbreeding depression and tested the performance of selfed and outcrossed offspring in two microbial environments, i.e. in soil inoculated with (i) non-sterile substrate from the same species (‘home’-conditions) and (ii) sterilised substrate.Plants produced more CL capsules than CH flowers. Pollinator exclusion had only small effects on CH seed production. CL seeds had a significantly lower mass per seed than CH seeds. This may be related to constraints in allocation or environmental conditions. Seedling growth was reduced in plants grown under ‘home’-conditions as compared to control soils. Under ‘home’-conditions, relative fitness of selfed seedlings of V. stagnina was significantly higher than that of crossed progeny. Our results suggest that high genetic differentiation among populations as a consequence of isolation may result in outbreeding depression, e.g., through biochemical or physiological incompatibilities between genes or the breaking of coadapted gene complexes. In V. stagnina, offspring fitness differed considerably between environments, but in general we found no indications for inbreeding depression in these rare species.