The effect of timing of pollination on the mating system and fitness ofKalmia latifolia (Ericaceae)

Plant mating systems are known to vary within species and some immediate ecological factors have been found to be associated with the geographic distribution of selfing. The environmental condition of the maternal plant may influence the production of selfed seed relative to outcrossed seed. This study investigated the effect of late pollination on the mating system of Kalmia latifolia, a long-lived perennial shrub. A 2 × 2 experimental design was used to determine whether reproductive success declines over the course of the flowering season and whether there was an interaction between pollination time (early vs. late in the season) and pollen type (self-fertilized vs. outcrossed). An interaction of this sort would indicate context-dependent fitness of selfed seeds compared to outcrossed seeds and, thus, show an ecological influence over a plant's mating system. Relative fitness was assessed in terms of female reproductive success. Timing of pollination did not affect abortion of outcrossed seeds; however, delay in pollination increased abortion of selfed seeds by 34.7%. Thus, it appears that plants selectively aborted selfed seeds rather than outcrossed seeds and this selection was more intense at the end of the season. An ecological factor such as time of pollination may affect the mating system of K. latifolia.     

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.     

Influence of selfing and maternal effects on life-cycle traits and dispersal ability in the herb Hypochaeris radicata (Asteraceae)

The ecological and evolutionary implications of dispersal are many. Pollination type and maternal effects may affect plant fitness traits, including life-cycle traits as well as dispersal ability. This study investigated the joint influence of pollination type and maternal effects on both life-cycle traits and dispersal ability in the herb Hypochaeris radicata . We conducted experimental crosses to obtain selfed and outcrossed progeny. Individual seeds and their pappuses were measured to determine seed terminal velocity. Seed size was also used to assess maternal effects. Selfing dramatically decreased seed set, indicating that H. radicata is self-incompatible. However, the few selfed seeds produced outperformed outcrossed seeds in seed size and flowering probability, surely as a result of an effective reallocation of resources among selfed seeds. None of the life-cycle traits was affected by seed size, the estimate of maternal effects. Selfed seeds were larger and bore a smaller pappus than outcrossed seeds. As a result, dispersal ability was lower for selfed than outcrossed seeds. Several factors, such as the low proportion of plants that produced selfed seeds, the low number of selfed seeds produced per plant, and the lack of self-fertility mechanisms might act in concert to prevent the evolution of selfing in H. radicata .  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 163–170.     

The mating system and relative performance of selfed and outcrossed progeny in Arabis fecunda (Brassicaceae)

We estimated rates of self-fertilization and inbreeding depression in the hermaphroditic perennial Arabis fecunda. Crosses were made on mesh-bagged wild plants, yielding 12 plants producing self-, outcross-, and naturally fertilized seeds that were then grown in a greenhouse. Analysis of variance indicated aboveground dry weight at 160 days differed among pollination treatments, but mean seed weight, number of seeds per fruit, and days to germination did not. For dry weight, selfed progeny have 9.4% reduction and naturally pollinated progeny a 3.7% reduction compared to outcrossed progeny, suggesting a 39% selling rate in Arabis. Significant inbreeding depression and a mixed mating system are evidence that the deleterious effects of self-fertilization are maintained through high rates of mildly deleterious mutation. Significant maternal-parent-by-pollination-treatment interactions for mean seed weight and dry weight are consistent with inbreeding depression caused by deleterious recessives and varying past maternal inbreeding.     

THE RELATIVE COSTS OF SELF- AND CROSS-FERTILIZED SEEDS IN IMPATIENS CAPENSIS (BALSAMINACEAE)

By using a generally applicable technique that involves monitoring the development and survivorship of flowers and seed capsules, I estimated the material and energetic costs of producing self- and cross-fertilized seeds in Impatiens capensis. All flowers and fruits on six plants were censused intensively for the two-month period of reproduction. Cleistogamous (selfing) flowers ripened seed in about 24 days, compared to about 36 days for the chasmogamous (outcrossing) flowers. In terms of dry weight, selfed seeds cost about two-thirds as much as outcrossed seeds: 12.4 versus 18.4 mg dry weight per seed. When adjusted to the currency of calories, and including an independent estimate of pollen and nectar production in outcrossing flowers, I estimate the costs to be about 65 and 135 calories per selfed or outcrossed seed. Sources of error include the accuracy of the estimates of flower and fruit weight, and possible differences among the developmental stages in respiratory costs. The cost discrepancy implies that outcrossed seeds should possess a countervailing fitness advantage large enough to offset their greater energetic cost.     

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.     

GYNODIOECY IN SILENE VULGARIS (CARYOPHYLLACEAE): PROGENY SUCCESS,EXPERIMENTAL DESIGN,AND MATERNAL EFFECTS

This study documents the comparative success of seeds and seedlings of the perennial gynodioecious-gynomonoecious weed, Silene vulgaris, in the greenhouse. The importance of experimental design is stressed by comparing two different statistical analyses of the data. Seeds were obtained from artificial pollinations in the field: self-fertilization of hermaphrodites, and cross-fertilizations of both hermaphrodites and females. One-way analysis of variance using progeny type (selfed hermaphrodites, outcrossed hermaphrodites, and outcrossed females) as the treatment effect for each seed and seedling variable showed statistically discernable differences among progeny from different cross types. The significance of this type of ANOVA resulted from a reduced error term and positively-biased F ratios. A factorial design showed no significant differences due to type of progeny in seed mass, days to germination, leaf number, area, or biomass at six weeks of age. There were, however, significant differences among seeds attributable to maternal parent for all seed and seedling variables. A higher proportion of seeds from outcrossed individuals germinated compared to that from self-fertilization. When the data were analyzed to include and partition all sources of variation, differences among offspring appeared during germination, rather than during later development. Seed mass, cross type, and sex of maternal parent all significantly affected the likelihood of germination; however, they had decreasing predictive power, respectively. Inbreeding depression in Silene vulgaris may help maintain gynodioecy; however, the pleiotropic effects of both nuclear and cytoplasmic genes for sex expression also may affect fitness and the maintenance of females.     

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.     

The effects of pollen composition on fitness components in a neotropical herb

Summary Experimental pollinations of Costus allenii (Zingiberaceae) were conducted to assess the effects of pollen composition on fitness. Plants were selfed, outcrossed with the first nearest neighbor, and outcrossed with pollen mixtures obtained from the nearest 2, 3, and 5 plants. Cross type had a significant effect on seed production, seed weight and total-plant dry weight. Progeny from crosses with 3, and 5 parents grew significantly larger than selfed progeny, or those from 1-parent crosses. Competition experiments indicated the superiority of progeny from 3-, and 5-parent crosses over progeny from 1-parent crosses, but no differences in competitive ability were observed between progeny from 3-, and 5-parent crosses. Relative fitness, based on 1) seed production, 2) percent germination, and 3) dry weight, varied significantly among crosses, and was greatest for crosses with 3 parents and lowest for selfs. The relative fitness of progeny from 5-parent crosses was lower than that of all other outcrossed classes. We suggest that the significant effect of pollen composition on fitness results from variation in the genetic similarity of seed and pollen parents, which is a function of spatial distribution and population structure.     

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.     

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.     

The Effect of Pollen Source vs. Flower Type on Progeny Performance and Seed Predation under Contrasting Light Environments in a Cleistogamous Herb

Dimorphic cleistogamy is a specialized form of mixed mating system where a single plant produces both open, potentially outcrossed chasmogamous (CH) and closed, obligately self-pollinated cleistogamous (CL) flowers. Typically, CH flowers and seeds are bigger and energetically more costly than those of CL. Although the effects of inbreeding and floral dimorphism are critical to understanding the evolution and maintenance of cleistogamy, these effects have been repeatedly confounded. In an attempt to separate these effects, we compared the performance of progeny derived from the two floral morphs while controlling for the source of pollen. That is, flower type and pollen source effects were assessed by comparing the performance of progeny derived from selfed CH vs. CL and outcrossed CH vs. selfed CH flowers, respectively. The experiment was carried out with the herb Ruellia nudiflora under two contrasting light environments. Outcrossed progeny generally performed better than selfed progeny. However, inbreeding depression ranges from low (1%) to moderate (36%), with the greatest value detected under shaded conditions when cumulative fitness was used. Although flower type generally had less of an effect on progeny performance than pollen source did, the progeny derived from selfed CH flowers largely outperformed the progeny from CL flowers, but only under shaded conditions and when cumulative fitness was taken into account. On the other hand, the source of pollen and flower type influenced seed predation, with selfed CH progeny the most heavily attacked by predators. Therefore, the effects of pollen source and flower type are environment-dependant and seed predators may increase the genetic differences between progeny derived from CH and CL flowers. Inbreeding depression alone cannot account for the maintenance of a mixed mating system in R. nudiflora and other unidentified mechanisms must thus be involved.     

Seed production from the mixed mating system of Chesapeake Bay (USA) eelgrass (Zostera marina; Zosteraceae)

In monoecious plants, gametes can be exchanged in three ways: among unrelated genets (outbreeding), with close relatives (inbreeding), or within individuals (geitonogamous selfing). These different mating systems may have consequences for population demography and fitness. The experiment presented herein used artificial crosses to examine the mating system of Chesapeake Bay, Virginia, USA eelgrass (Zostera marina L; Zosteraceae), a bisexual submerged aquatic plant that can outbreed, inbreed, and self. Genetic data indicate severe heterozygosity deficiencies and patchy genotype distribution in these beds, suggesting that plants therein reproduce primarily by vegetative propagation, autogamy, or geitonogamy. To clarify eelgrass reproductive strategies, flowers from three genetically and geographically distinct beds were hand-pollinated in outbred, inbred, and selfed matings. Fertilization success and seed production, life history stages which contribute greatly to the numeric maintenance of populations, were monitored. We found no evidence that inbreeding had negative consequences for seed production. On the contrary, selfed matings produced seeds significantly more frequently than outcrossed matings and produced significantly larger numbers of seeds than either inbred or outbred matings. These results contrast with patterns for eelgrass in other regions but might be expected for similar populations in which pollen limitation or a short reproductive season renders selfing advantageous.     

DISTANCE BETWEEN MATES AFFECTS SEEDLING CHARACTERS IN A POPULATION OF IMPATIENS CAPENSIS (BALSAMINACEAE)

We tested for the presence of an optimal outcrossing distance in a population of Impatiens capensis, an annual herb that possesses a mixed mating system, by measuring fitness components for offspring of parents that were separated by distances of 2, 10, or 50 m. Heavier seed weights and later seed maturation enhanced probabilities of emergence and subsequent survival, but emergence and survival were unaffected by outcrossing distance. Path analysis showed that most characteristics of seeds and seedlings were positively correlated. Effects of maternal family were strong through the first month of growth. Analyses of covariance reveal that, as anticipated, the effects of maternal family, seed weight, and seed maturation date declined over time. Seeds that were produced late in the season were heavier than early seeds, and late seeds germinated at later dates than early seeds. Surprisingly, although late germination dates were associated with taller plants after 1 and 3 months of growth, late germination resulted in lighter dry weights at maturity. The distance between parents had a negative direct effect on seed weight but a positive effect on height after 1 month. Height at 1 month responded positively to outcrossing distance and negatively to the square of distance when seed weight, collection date, and maternal family were held constant. This implies an optimal outcrossing distance for height at 1 month, which we estimate as 29 m using a quadratic procedure. However, path analysis suggests that the apparent optimum is due to a negative correlation between the interparent distance and seed weight.     

Inbreeding depression in Lychnis flos-cuculi (Caryophyllaceae): effects of different levels of inbreeding

In a controlled crossing experiment on Lychnis flos-cuculi plants in the greenhouse, outbred and selfed maternal plants were each treated with pollen from unrelated plants, siblings and selves. The seeds thus obtained had expected inbreeding coefficients of 0, 0.25 and 0.5 for the outbred maternal plants, and 0, 0.5 and 0.75 for the selfed maternal plants. Seed abortion rate, seed weight and germination rate were estimated. Seedlings were transplanted to an outdoor garden, and monitored for survival, probability of flowering, number of capsules and area of capsules next spring. Inbred seeds germinated slower and in lower proportions than those less inbred, and seedlings had lower survival, flowering, fruit set and area of capsules if inbred. Combined fitness values were estimated from the survival and fecundity components, and severe inbreeding depression was detected for these estimates (0.51 and 0.56 for one generation of selfing). The fitness function decreased linearly with the increase in inbreeding coefficient, which is as expected if the inbreeding depression is additive among loci.     

Inbreeding depression and dominance-suppression competition after inbreeding in rapeseed (Brassica napus)

Rapeseed plants, of the summer annual variety Topas, that had been selfed twice consecutively were compared to outcrossed half-sibs for inbreeding depression in a rapeseed population at mating equilibrium. The effect of dominance-suppression competition was included in the effect of inbreeding. Both female-and male-fitness characters showed significant inbreeding depression. Biomass decreased 17% with inbreeding and was highly correlated with seed weight. The total number of flowers decreased 15% with inbreeding. There was a significant effect of lines. The possible importance of experimental design in studies that estimate inbreeding depression is discussed.     

THE IMPACT OF ELECTROPHORETIC GENOTYPE ON LIFE HISTORY TRAITS IN PINUS TAEDA

Reports of positive associations between allozymic heterozygosity and measures of fitness are routine, but it has not been possible to distinguish between the two preeminent explanations of the phenomenon, dominance and overdominance. We tested several of the assumptions of these hypotheses in our study of the relationship between electrophoretic genotype and three life history traits in loblolly pines (Pinus taeda L.). Traits examined included the survival and growth of selfed and outcrossed progeny of 45 maternal trees, and maternal fecundity, measured as the number of surviving progeny per mother tree. Inbreeding depression was severe; the relative fitness of the selfed progeny was only 8% that of the outcrossed progeny. We found a heterozygote fecundity advantage, which should have resulted in an excess of rare alleles in the progeny. Instead, there was evidence of severe survival selection against rare alleles in both heterozygous and homozygous forms. The deficit of rare alleles averaged 69 and 50% in the selfed and outcrossed progeny, respectively. The one allele in the sample that we should have suspected of being maintained by overdominance (a PGI2 mid-frequency allele) appeared to be overdominant for outcrossed height growth and probably for fecundity as well. Multiple-locus genotype explained very little of the variation in growth, however, and rather than seeing evidence for overdominance as a force in maintaining most of the observed polymorphism, we were left to explain, in the face of the severe survival selection, why the rare alleles were present at all. Projection of the stand into the future through computer simulation showed how balancing selection acting on differential growth, fecundity, and mortality among genotypes could, over the life of the stand, account for the maintenance of the rare alleles in the population.     

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.     

The mixed mating system of Impatiens capensis and infection by a foliar rust pathogen: patterns of resistance and fitness consequences

Outcrossing by hosts may offer protection from natural enemies adapted to parental genotypes by creating diverse progeny that differ from their parents through genetic recombination. However, past experimental work addressing the relationship between mating system and disease in offspring has given conflicting results, suggesting that outcrossing might also cause the dissolution of resistant genotypes. To determine if selfed progeny are more susceptible to disease caused by the heteroecious rust, Puccinia recondita, or if selfing preserves existing resistant genotypes, we used a factorial design to compare levels of infection of selfed and outcrossed progeny of Impatiens capensis, a woodland annual with a mixed mating system. We compared the level of host infection when exposed to three pathogen sources in the field: the sympatric rust population, and two allopatric rust populations. Outcrossed progeny exposed to sympatric rust had higher infection scores than selfed progeny exposed to the same rust, suggesting that outcrossing breaks up resistant genotypes. In addition, there was a trend for the rust to be more infective on sympatric rather than allopatric hosts. We also examined whether rust infection differentially alters the fitness of selfed and outcrossed progeny. Outcrossed plants that escaped infection had higher fitness, as measured by fruit production, than selfed plants, but there was no difference in fitness between infected selfed and infected outcrossed plants. Thus, outcrossing was advantageous in the absence of disease, but there was no fitness difference between selfed and outcrossed progeny in the presence of disease. In sum, our results indicate that interactions with pathogens can eliminate or reverse the advantage of outcrossing.     

Fitness components and the determinants of fecundity in populations of a native perennial grass (Tridens flavus)

Understanding intraspecific variation in traits that determine fitness is foundational to a trait-based approach to plant ecology. This study examined fitness components during 3 years of reproduction in a polycarpic perennial bunchgrass (Tridens flavus) native to eastern North America that could prove useful in revegetating disturbed habitats. Plants were cultured from seeds of five populations in central New Jersey, USA, and planted in July 2015 into two undisturbed gardens 30 m apart that differed in availability of sunlight and soil moisture. Following flowering in 2016, 2017 and 2018, the number of panicles, seed set, seed number (fecundity) and seed mass were recorded. Final dry aboveground mass was determined. Seed set was high (>70%) in all populations and gardens. Panicle production varied with population and was strongly correlated with fecundity, but populations were not differentiated for other fitness components. Panicle and seed number were greatest in the drier garden with greater daily light availability. Mass per seed was reduced as more seeds were produced in the second and third year but showed low variation compared to fecundity. Vegetative mass was the most important variable determining fecundity. Close proximity of sampled sites and an outcrossed, wind-pollinated mating strategy may have precluded detection of differentiation among T. flavus populations in the common gardens. High seed set, prodigious seed production on multiple panicles and high seed germinability and overwinter survival account for the occurrence of large populations of this native grass along roadsides and within successional fields and young woodlands throughout the region.