Consequences of a mixed reproductive system in the hog peanut,Amphicarpaea bracteata, (Fabaceae)

Summary The forest annual, Amphicarpaea bracteata L. can reproduce via aerial chasmogamous, aerial cleistogamous, and subterranean cleistogamous flowers. Both plant size and light intensity influenced the utilization of the three modes of reproduction. chasmogamous and aerial cleistogamous flower number and the ratio of chasmogamous flowers to the total number of aerial flowers increased with plant size. The latter demonstrated a shift to xenogamy and outbreeding in larger plants. Light intensity indirectly influenced reproductive modes through its infuence on plant size. Seed set by both types of aerial flowers was low and unrelated to plant size. Subterranean seed number and the total dry weight of subterranean seeds per plant increased with size. The subterranean seeds of Amphicarpaea bracteata are thirty-four times larger than the aerial seeds (fresh weight). Under field conditions, subterranean seeds had greater germination after one year than acrial seeds. The plants arising from subterranean seeds were significantly larger and more fecund than those from aerial seeds. Seeds produced by aerial cleistogamous, hand selfpollinated chasmogamous, and naturally pollinated chasmogamous flowers had equivalent germination rates and produced plants of equal size and fecundity. This suggests that the outbred progeny from chasmogamous flowers have no advantage over the inbred progeny from aerial cleistogamous flowers.     

Evolution of floral dimorphism in a cleistogamous annual, <Emphasis Type="Italic">Impatiens noli-tangere</Emphasis> L. occurring under different environmental conditions

The resource allocation models for the evolution of a mixed production of cleistogamous and chasmogamous flowers were tested in four natural populations of Impatiens noli-tangere L. When we incorporated the estimated parameter values into our basic model, under the assumption that the environmental conditions did not change through the reproductive season, the model predicted the obligate chasmogamy in all four populations. However, including the fluctuation of the fertility of chasmogamous flowers in the model, the seasonal switching of chasmogamous and cleistogamous flower production becomes an evolutionary stable strategy, which explains the reproductive behavior of the individuals in two populations. Only after the relationship between the geitonogamy of chasmogamous flowers and the number of chasmogamous flower production was considered in the model did the simultaneous production of both of the dimorphic flowers become an evolutionary stable strategy. Further, the complete model clarifies the reproductive behavior of the individuals in the other two populations.     

The interactive effects of herbivory and mixed mating for the population dynamics of Impatiens capensis

In this study, we examine the demographic consequences of mixed mating and explore the interactive effects of vegetative herbivory and mating system for population dynamics of Impatiens capensis, a species with an obligate mixed mating system (i.e., individuals produce both obligately selfing cleistogamous and facultatively outcrossing chasmogamous flowers). In two natural populations, we followed seeds derived from cleistogamous and chasmogamous flowers subject to different herbivory levels throughout their life cycle. Using a mating system-explicit projection matrix model, we found that mating system types differed in important vital rates. Cleistogamous individuals had higher rates of germination than did chasmogamous individuals, whereas chasmogamous individuals expressed a fecundity advantage over cleistogamous individuals. In addition, population growth was most sensitive to changes in vital rates of cleistogamous individuals, indicating the demographic importance of selfing for these populations. Herbivory also had demographic consequences; a 33%-49% reduction in herbivory caused the population growth rates to increase by 104%-132%, primarily because of effects on vital rates of selfed individuals. Our results not only uncover a novel consequence of mating system expression, that is, mating system influences population dynamics, but also shed light on the role of herbivores in maintaining mixed mating.     

Is plasticity across seasons adaptive in the annual cleistogamous plant Lamium amplexicaule?

Background and aims Many angiosperms exhibit cleistogamy, the production of both cleistogamous flowers (CL), which remain closed and obligately self-pollinated, and chasmogamous flowers (CH), which are potentially open-pollinated. The CH proportion can be plastic. Plasticity is adaptive if environmental changes can be reliably assessed and responded to with an appropriate phenotype and if plastic genotypes have higher fitness in variable environments than non-plastic ones.Methods We studied the plastic response of four natural populations from northern and southern France of an annual cleistogamous plant, Lamium amplexicaule, to predictable seasonal variation. Plants were grown in a semi-controlled environment in spring and in autumn. We assessed the variation in flower number, phenology and cleistogamy-related traits, which were all plastic with respect to season. The CH proportion was higher in spring than in autumn in all four populations.Key Results We showed significant stabilizing selection for cleistogamy traits, with higher optimal CH proportions and more pronounced stabilizing selection in spring than in autumn. Observed CH proportions were close to the predicted optimal CH proportions in each season except in autumn for southern populations, which do not experience the autumnal growing season in nature.Conclusions These results are consistent with adaptive plasticity across seasons of cleistogamy in L. amplexicaule. We propose that adaptive plasticity of cleistogamy could be driven by pollination environment variation, with CL flowers providing reproductive assurance when pollinators are scarce and CH flowers reducing the inbreeding depression in offspring when pollinators are abundant.     

Herbivory and competition interact to affect reproductive traits and mating system expression in Impatiens capensis

As a step toward understanding how community context shapes mating system evolution, we investigated the combined role of two plant antagonisms, vegetative herbivory and intraspecific competition, for reproduction and mating system expression (relative production of selfing, cleistogamous and facultatively outcrossing, chasmogamous flowers and fruits) of Impatiens capensis. In a survey of I. capensis populations, we found that vegetative herbivory and intraspecific competition were positively correlated. In a greenhouse experiment where leaf damage and plant density were manipulated, multispecies interactions had dramatic effects on reproductive and mating system traits. Despite having additive effects on growth, herbivory and competition had nonadditive effects for mating system expression, chasmogamous fruit production, flower number and size, and cleistogamous flower production. Our results demonstrate that competitive interactions influence the effect of herbivory (and vice versa) on fitness components and mating system, and thus antagonisms may have unforeseen consequences for mating system evolution, population genetic diversity, and persistence.     

Heterocarpy in Salvia roemeriana (Lamiaceae)

Although Salvia roemeriana has long been known to produce both chasmogamous and cleistogamous flowers, the mericarps resulting from those flowers have received little attention. We germinated seeds from chasmogamous and cleistogamous flowers, recorded germination times, and fit time‐to‐germination, three‐parameter log‐logistic regressions to analyze differences in germination progress. Additionally, we compared the mass and size of mericarps from both kinds of flowers. Our results show that the mericarps produced from chasmogamous flowers are larger and heavier than those from cleistogamous flowers. In addition, seeds from chasmogamous flowers had a longer dormancy than those from cleistogamous flowers. This is the first report of heterocarpy in Salvia and in the family Lamiaceae. Together, cleistogamy and heterocarpy are a multiple strategy that may be advantageous in heterogeneous environments.     

Herbivory alters the expression of a mixed-mating system

The direct and indirect effects of vegetative herbivory on the mating system of Impatiens capensis were analyzed through a survey of herbivory in natural I. capensis populations and manipulation of leaf damage in the field. Across 10 wild populations of I. capensis proportion of cleistogamous flowers had a significant positive exponential relationship with natural levels of herbivory. Similarly, experimental leaf damage increased the proportion of flowers and seeds that were cleistogamous. Leaf damage also reduced the biomass of cleistogamous progeny more severely relative to that of chasmogamous progeny. The cumulative effect of leaf damage was to increase plant reliance on fitness derived from cleistogamous progeny. Leaf damage indirectly affected mating system traits by reducing chasmogamous flower size, leading to a reduction in pollinator visitation. Under these experimental conditions, herbivory did not significantly reduce the number of simultaneously open flowers and potential for geitonogamy, nor did it result in significant changes in the composition of the pollinator fauna. These findings are among the first to demonstrate that herbivory has consequences for mating system and should be considered a factor shaping mating system evolution.     

Cleistogamy in Scutellaria indica (Labiatae): effective mating system and population genetic structure

Scutellaria indica is a perennial herb with both chasmogamous (CH) and cleistogamous (CL) flowers on the same plant in some populations, and only CL flowers in other populations. Actual seed production by CH and CL flowers was investigated in populations of S. indica. The average seed set of CL flowers was 19 times higher than CH flowers, indicating much greater fertilization success. The CL seeds were also significantly heavier than the CH seeds. However, the resource cost of producing a CH flower was much higher than that of producing a CL flower. The CH flower was approximately seven times larger, and its pollen/ovule ratio was approximately five times higher than flowers. The level and pattern of genetic diversity at both allozyme and random amplified polymorphic DNA (RAPD) levels were consistent with a predominantly selfing system in the species. The average amount of within-population genetic variation was extremely low (A = 1.025, P = 2.36%, HO = 0.001 and HE = 0.008 based on allozyme data, and P = 8.94% and HE = 0.03 based on RAPD data). At the species level, the estimates of total gene diversity (HT) were 0. 101 based on allozyme data and 0.139 based on RAPD data. A very high level of genetic differentiation occurred between populations (allozyme GST = 0.92 and RAPD GST = 0.81). Genetic drift coupled with predominant cleistogamous selfing apparently played the major role in determining the population genetic structure in S. indica. Although the features associated with CH and CL flower and seed production seem to be sufficient for the evolution of complete cleistogamy in S. indica, random fixation of alternative alleles for dimorphic or complete cleistogamy in small populations could maintain the multiple strategy of chasmogamous and cleistogamous reproduction in the species.     

Chasmogamous and Cleistogamous Pollination in Salpiglossis sinuata

Pollen from chasmogamous flowers of Salpiglossis sinuata L. could not be induced to germinate in vitro unless stigmatal extract was applied to the culture medium. The substance that induces pollen germination in the stigmatal extract is water-soluble and heat-stable. Crosses could not be achieved between chasmogamous and cleistogamous flowers because of structural incompatibility. Pollinated pistils of chasmogamous flowers release a large amount of ethylene. The burst of ethylene release is due to an interaction between pollen tubes and stylar tissue and is directly proportional to the quantity of pollen placed on the stigma. Cleistogamous flower buds also produce a burst of ethylene at the time of pollination within the closed flower. The ethylene release may be a cause of reduced corolla development associated with cleistogamous flowers.     

Cleistogamy in the rare high Andean perennial herb Cryptantha capituliflora (Boraginaceae)

 Axial and apical flowers of Cryptantha capituliflora were analyzed with regard to morphology and pollen tube growth to assess the occurrence of cleistogamy. Although intermediate floral forms do occur, cleistogamous flowers were significantly smaller than chasmogamous flowers, had fewer anthers, and showed a distinctive stigmatic surface. Chasmogamous flowers can be cross-pollinated. Nevertheless, the growth of self-pollen tubes in few chasmogamous buds jointly with flower characters suggests that these flowers can probably produce fruits through autonomous selfing. The mean seed number per fruit did not differ between fruits from chasmogamous and cleistogamous flowers. Cleistogamous flowers were only observed in axial inflorescences, which are completely covered by the leaf. Other species of section Cryptantha also show the same trend, with cleistogamous flowers located in the lower half of the stems. This pattern is discussed in relation to dissimilarities in the outcrossing opportunities between flower types within the plant. Received May 22, 2002; accepted November 14, 2002 Published online: March 20, 2003     

Failure of reproductive assurance in the chasmogamous flowers of Polygala lewtonii (Polygalaceae), an endangered sandhill herb

Hypothetically, a species with both cleistogamous (CL) flowers and delayed selfing chasmogamous (CH) flowers should display high levels of reproductive assurance because, over time, obligate selfing by CL flowers should reduce inbreeding depression and delayed selfing in CH flowers should compensate for the absence of outcross pollen. We used pollinator-exclusion experiments to investigate reproductive assurance in the CH flowers of Polygala lewtonii, an herb with a mixed mating system. We followed CH flowers from bud-break to flower/fruit abscission to quantify fruit initiation and maturation and rates of floral development. We also evaluated the efficacy of the selfing mechanism, conducted pollinator watches to assess the likelihood of pollinator limitation, and performed regression analysis to determine the effect of flower position on fruit production. Pollinator exclusion significantly reduced fruit initiation and maturation. Investigation of floral development demonstrated that the selfing mechanism is largely dysfunctional in CH flowers, indicating the failure of reproductive assurance. Low observed rates of insect visitation appear to contradict high rates of CH fruit production in open-pollinated plants, particularly given the rarity of delayed selfing. In both treatments, flower position significantly affected fruit initiation, suggesting a role for resource limitation in both pollinator-excluded and open-pollinated flowers.     

Outcrossing and paternity in Glycine argyrea by paired fruit analysis

Glycine argyrea (Fabaceae), a perennial wild relative of soybean, has a dual flowering strategy of both self-fertilized cleistogamous flowers and chasmogamous flowers on the same plant. Using allozyme polymorphisms the frequency and pattern of outcrossing was determined. The genotypes of seeds from each of several fruit (legumes) per plant were analysed by starch gel electrophoresis, and the maternal genotype inferred. The maximum likelihood estimates of outcrossing rate for the chasmogamous flowers averaged 0.38. The observed level of heterozygosity in the adult population (h = 0.25) compared with the level expected under random mating (h = 0.32) indicated that partial outcrossing was typical of this population. To analyse the mating pattern further, the pollen genotypes of several seeds per legume for pairs of legumes from the same plant were determined. About 35% of fruit from chasmogamous flowers had no genetically detectable outcross progeny, presumably because they were not cross-pollinated effectively. The majority of the remaining fruit had seed which were of mixed origin (both self-fertilized and outcrossed), suggesting that insect pollination does not preclude self-fertilization. As might be expected from this entomophilous pollination system, the pollen of outcrossed seed within one fruit usually (85% of cross-pollinated legumes) came from one male source. Evidence of pollen carry-over was found in the other legumes. The joint distribution of male sources among the pairs of legumes (paired fruit analysis) showed that non-self sources were shared in 30% of pairs. The probability that two outcrossed seeds from the same fruit would be half-sibs was estimated as 0.15, and for two seeds from different fruit on the same plant as 0.42. There is a hierarchy of genetic identity within and among legumes on the same plant, and on different plants, providing scope for the operation of selection at different levels.     

Plasticity in the reproductive strategy of a clonal cleistogamous species, <Emphasis Type="Italic">Pseudostellaria heterophylla</Emphasis>

The presence of cleistogamous and chasmogamous flowers on the same plant individual is considered to represent a “mixed” reproductive strategy. If a cleistogamous species also exhibits clonal propagation, then competition for limited resources is assumed to exist among the three reproductive modes. To date, however, the relationships and interactions among cleistogamous, chasmogamous, and clonal modes of reproduction have received little attention. In this study, we performed manipulative experiments to investigate the interactions among these different types of reproduction in the perennial herbaceous plant species Pseudostellaria heterophylla. The results showed that 66.4%–87.6% of individuals produce chasmogamous flowers and that the fruiting rates of these flowers in each surveyed population were between 23.5% and 77.4%. Furthermore, we found that 8.3% of the individuals of this species show inbreeding depression. We also detected significant negative correlations between the production of chasmogamous and cleistogamous flowers and between cleistogamous flower production and root tuber mass. However, chasmogamous flower production in an individual plant was found to have little influence on its subsequent clonal propagation. We propose that the plasticity of reproductive strategies observed in P. heterophylla is due to changes in the resource pool and resource allocation.     

Effects of light and nutrient availability on chasmogamy and cleistogamy in an understory tropical herb,Calathea micans (Marantaceae)

The effects of light and nutrient availability on chasmogamous and cleistogamous flower and fruit production were investigated in an understory tropical herb, Calathea micans (Marantaceae). I censused chasmogamous and cleistogamous flower and fruit production at five permanently marked demographic study sites in Costa Rica, characterized by different successional stages. Using a transplant experiment, I examined whether an increase in light and/or nutrients would increase chasmogamous and/or cleistogamous flower production. In natural populations as well as in the experiment, chasmogamous reproduction increased with light; nutrient availability significantly increased chasmogamous reproduction in the transplant experiment. Field observations indicated that very few plants reproduced and low investment in reproduction might have been due to poor environmental conditions. Larger plants had a higher probability of reproducing, but plant size did not have an effect on the mode of reproduction, chasmogamy vs. cleistogamy. However, the production of new vegetative shoots increased the probability of producing chasmogamous inflorescences. Cleistogamy may allow the plant to reproduce even in conditions of poor habitat quality and assures some seed set even in conditions unfavorable to plant growth.     

Why is there variation in mean seed size among plants within single populations? test of the fertilization efficiency hypothesis

We tested the fertilization efficiency hypothesis, which attempts to explain mean seed size variation among plants within single populations, by comparing the patterns of seed size variation between chasmogamous (CH) flowers and cleistogamous (CL) flowers in Impatiens noli-tangere and Viola grypoceras, respectively. The fertilization efficiency hypothesis predicts that larger plants produce larger seeds if the number of pollen grains captured by a plant increases with increased allocation of resources to its attractive structures (e.g., corolla and nectar), but with diminishing gains. Thus, seed size should depend on plant size in seeds from CH flowers because of the diminishing gains of capturing pollen in these flowers, whereas seed size should not depend on plant size in seeds from CL flowers because CL flowers need not capture outcross pollen. We found significant positive correlations between mean seed size per plant and plant size for seeds from CH flowers in both species. However, there was no significant positive correlation between these two factors for seeds from CL flowers of both species. The results of the present investigations were thus consistent with the fertilization efficiency hypothesis.     

Cleistogamy as a bet‐hedging strategy in Oxalis acetosella, a perennial herb

1 Phenology and reproduction were studied in three populations of the cleistogamous herb Oxalis acetosella during three growing seasons, in order to see how the balance between chasmogamous (CH) and cleistogamous (CL) reproduction varies with temporal and spatial environmental variation and with plant size. The numbers of CH and CL flower buds, flowers, immature capsules and mature capsules were counted per ramet, ramet sizes were estimated, and mature capsules were collected for seed counts.
2 Both CH and CL flower numbers were positively correlated with ramet size expressed as leaf number, but the correlation was much stronger in the CL phase. CL flower production also varied significantly between years and sites. Thus, CL production in O. acetosella was not independent of resources and climatic variation.
3 When the effects of year and site were taken into account, the probability of an individual flower developing into a mature fruit was not higher in the CL phase than in the CH phase.
4 CL production was affected by fertilization success in the CH phase. Ramets with one or more CH flowers left unfertilized generally produced more CL buds than ramets with all their CH flowers fertilized. The former group also tended to have more seeds per CL capsule.
5 Since reproductive success in the two phases varies in different temporal and spatial patterns, cleistogamy in O. acetosella is considered to be a bet‐hedging strategy optimizing reproductive output in fluctuating environments.
6 The findings of this study are in conflict with the general view on cleistogamy as a fail‐safe mechanism for back‐up seed production, unaffected by variations in resource supply and environmental conditions.     

INTRA-INFLORESCENCE VARIABILITY IN POLLEN/OVULE RATIOS IN THE CLEISTOGAMOUS SPECIES LAMIUM AMPLEXICAULE (LABIATAE)

A comparative study was made of the various floral forms in the main shoot inflorescence of the cleistogamous species Lamium amplexicaule L. (Labiatae). This study revealed significant differences in pollen/ovule (P/O) ratios between successively produced flowers. The variation in P/O ratio is due to a change in pollen count/flower and not in ovule number. The study included two plant populations, one grown in November when only closed flowers are produced, and the other grown in April when open flower production occurs at the upper nodes. The intra-inflorescence variation in P/O ratio among the spring population showed a correlation between P/O ratio and breeding system. The cleistogamous flowers had low P/O ratios of about 200 while the chasmogamous flowers had higher P/O ratios of about 600.     

Reproductive investment in a cleistogamous morph of <Emphasis Type="Italic">Polygonum jucundum</Emphasis> (Polygonaceae)

Cleistogamy, a breeding system with permanently closed and self-pollinated flowers, is expected to assure reproductive success at a lower cost. Previous studies have inferred the occurrence of cleistogamous flowers in Polygonum, but there are no detailed studies on their reproductive investment compared with that of the chasmogamous flowers in this genus. Here, we studied a cleistogamous morph of P. jucundum to investigate the investment in pollen number, tepal and nectary size. The number of pollen grains per flower was counted with a light microscope. Nectaries and perianths were observed via scanning electron microscope and light microscopy, photographed and measured via ImageJ. The perianths of the cleistogamous flowers, as well as the pollen numbers and nectary sizes, were significantly smaller than those of the chasmogamous flowers. The pollen numbers of the CL flowers were seven times lower than those in the CH flowers. The tepal areas of the CL flowers were, on average, approximately 38% those of the CH flowers. The nectary areas of the CH flowers were almost twice those of the CL flowers. In addition, the nectaries of the cleistogamous flowers were degenerated and inconspicuous, in distinct contrast with the well-developed and conspicuous nectaries of the chasmogamous flowers. Self-fertilization was completed and produced seeds. The cleistogamous P. jucundum, compared with chasmogamous individuals, exhibited lower costs in male function, pollinator attraction and reward structure investment. This cleistogamy appears to be favourable for the plant reproduction under suboptimal conditions.     

Reproductive Biology of an Amphicarpic Annual, Polygonum thunbergii (Polygonaceae): Spatio-temporal Changes in Growth, Structure and Reproductive Components of a Population over an Environmental Gradient

Abstract The process and mechanisms of spatio-temporal changes in growth, population structure, as well as various yield and reproductive components of a population of an amphicarpic annual, Polygonum thunbergii (Polygonaceae), with two reproductive systems (aerial chasmogamous flowers and subterranean cleistogamous flowers) along an environmental gradient (light, moisture and soil nitrogen levels) were investigated in the field.
The results clearly demonstrate that growth and allocation patterns, population structure, and reproductive output of individuals changed sharply along the environmental gradient in response to seasonal and spatial changes in resource availability. Models predicted that light conditions bring about one-sided competition, whereas nutrient conditions in the soil engender two-sided competition. As expected, the degree of one-sided competition was prominent in the case of a planophile, Polygonum thunbergii. Allocation patterns, seed outputs, individual seed size as well as relative energy costs of chasmogamous and cleistogamous seed as affected by light and nutrient levels were also critically analyzed. The most noteworthy finding was that the size of chasmogamous seeds sharply decreased in response to a decrease in the light regime, while cleistogamous seed size remained constant along the gradient. However, relative cost of both chasmogamous and cleistogamous seeds sharply increased with decrease in the light level, reflecting different degrees of environmental stress, biotic interference, or both.     

Analysis of mating system and genetic structure in the endangered,amphicarpic plant,Lewton’s polygala (<Emphasis Type="Italic">Polygala lewtonii)</Emphasis>

Polygala lewtonii is a federally endangered, amphicarpic plant with a mixed mating system and three types of flowers: (1) aboveground, chasmogamous flowers (i.e., open-pollinated; CH), (2) aboveground, cleistogamous flowers (i.e., closed, selfing; CL) and (3) CL flowers on belowground stems (amphicarpy). Aboveground seeds are ant-dispersed, whereas belowground seeds are spaced across the length of the rhizome. Here, we collected individuals of P. lewtonii at both range-wide and fine geographic scales and genotyped them at 11 microsatellite loci. We analyzed patterns of genetic diversity and structure to understand: (1) the predominant mating system (selfing or outcrossing), (2) the movement of pollen and seeds across the landscape, and (3) the optimal strategy to conserve the full range of genetic variation. P. lewtonii reproduces predominantly by selfing or bi-parental inbreeding, but reproduction occurred through each of the three flower types. Some individuals produced by selfing/inbreeding were tightly clustered spatially, and were likely produced either by belowground flowers or by aboveground flowers with limited seed dispersal. Other selfed/inbred individuals were spatially separated (maximum of 15 m), and were likely produced by aboveground flowers followed by seed dispersal by ants. Fine-scale patterns of genetic structure indicate that some gene flow is occurring among aboveground CH flowers but both pollen and outcrossed seeds are moving limited distances (maximum of 0.5 km). Because genetic variation is structured at a fine spatial scale, protecting many populations is necessary to fully conserve the genetic variation in P. lewtonii. Conservation seed banking, if accompanied by research on seed germination requirements, may also contribute to the effective protection of genetic variation in P. lewtonii.