COMPONENTS OF SEED AND POLLEN YIELD OF LOBELIA CARDINALIS: VARIATION AND CORRELATIONS

Plants from three Lobelia cardinalis populations were grown under common garden conditions to assess intra- and interplant variation in seed and pollen production. Seed number per flower and mean seed weight varied systematically with floral position on the inflorescence (lowest values were from terminal flowers) but pollen grain number per flower did not vary systematically with floral position. Most of the remaining variance in seed and pollen grain number per flower and mean seed weight was distributed among plants; clones produced very similar amounts of pollen and seed. Seed yield was positively correlated with seed production per flower and with total flower production, but not with mean seed weight; pollen yield was also positively correlated with pollen grain production per flower and total flower production. Seed and pollen yield were simple linear functions of plant size but only pollen yield was a simple linear function of flower production; seed yield was a quadratic function in which the second order term was negative. This quadratic relationship resulted from a negative correlation between seed number per flower and total flower production. This correlation, in addition to the wide variation among plants in pollen number per flower, accounts for the weak correlation of seed and pollen yield. I conclude from these data that it is unlikely that plants in natural L. cardinalis populations transmit genes to the population's seed crop equally through pollen and ovules—emphasizing the importance of measuring both male and female components of reproductive success.     

Pollen and resource limitations to lifetime seed production in a wild population of the endangered plant Disanthus cercidifollus var.Iongipes H.T.Chang (Hamamelidaceae)

Disanthus cercidifolius Maxim.var.longipes H.T.Chang,a plant species that only occurs in a few counties in Hunan,Jiangxi and Zhejiang Provinces and with a relatively small number of individuals,is ranked as a second Class endangered species for conservation in China.We have studied the effect of pollen and resources available to female reproduction,and the reproductive mechanism of "excess flowers with low fruit set" in Disanthus cercidifolius Maxim.var.longipes H.T.Chang was discussed.Results are as follows:Pollen from different sources has significant effects on fruit set and seed set of Disanthus cercidifolius Maxim.var.longipes H.T.Chang.The pollen source rather than pollen numbers significantly affected reproduction of this species.In wild populations,producing one fruit needs about 54.8 flowers,and one satiation seed needs about 6.60 flowers or 83.19 ovules.After fertilizing,which was propitious to flower development,the abortion rate of flower buds was decreasing,but the flowering rate was increasing.The fruit set and seed set was also significantly increasing,while abortion rate of fruit was significantly decreasing.With the increasing percentages of cutting leaves,the fruit set decreased,but the abortion rate of fruit shows no significant differentiation among treatments.After cutting branches that were puny,broken and insectinfested branches,the flower number seemed to be decreasing,but the fruit set and seed set all increased significantly.After removing some flowers,the fruit set was calculated with respect to the number of flowers remaining after the treatment increased with increasing of percentages of flower removal,whereas fruit set calculated with respect to the initial number of flowers remained constant,and the mean weights of per fi'uit and per seed all decreased significantly.Sufficient spatial or temporal heterogeneities in nutrient levels might allow limitation of seed set by resources and pollen in a natural population,while supplying resources may indirectly affect pollination by increasing attraction of the flowers to pollinators.There were very low fruit and seed sets in natural populations ofDisanthus cercidifolius Maxim.var.longipes H.T.Chang.Different factors may have interacted to effect a low fruit set.A joint adoption of the "selection abortion hypothesis","ovary reserve hypothesis" and "male function hypothesis" seems to be the most likely explanation for the reproductive strategy of"excess flowers with few fruit sets" in Disanthus cercidifolius Maxim.var.longipes H.T.Chang.     

INFLORESCENCE SIZE: TEST OF THE MALE FUNCTION HYPOTHESIS

One explanation for low fruit sets in plants with hermaphroditic flowers is that total flower production by a plant is controlled primarily by selection through male function. This male function hypothesis presupposes that success in pollen donation increases more strongly with flower number than does seed set. I tested this prediction by measuring male and female components of reproductive success as functions of flower number in natural populations of the self-incompatible, perfect flowered plant, Ipomopsis aggregata. Fruit set in this hummingbird-pollinated plant averaged 4.9 to 40.3% across the 4 years of study. Both the total amount of pollen donated and the total amount received, as estimated by movement of fluorescent powdered dyes, increased linearly with number of flowers on a plant. Total seed production, however, increased disproportionately quickly because plants with larger floral displays were more likely to set at least one fruit. An estimate of the functional femaleness of a plant, based on pollen donation and seed production, increased with flower number. These results do not support the male function hypothesis.     

Variation of pollination and resource limitation in a low seed-set tree, Liriodendron chinense (Magnoliaceae)

Pollen limitation and resource limitation have been documented as the major factors responsible for plants commonly producing more ovules than seeds, but few studies have examined pollen deposition directly in natural populations at different sites and times. We investigated the causes of low seed set in four populations of Liriodendron chinense (Magnoliaceae), an insect‐pollinated endangered tree endemic to southern China, over 2–3 years. One pistil potentially produces two ovules. The number of pistils per flower varies among populations, but in three of the four populations the variation in a given population was not significantly different among years. Overall, populations with higher pistil numbers tend to set more seeds per flower, but a positive correlation between pistil numbers and seed production per flower was observed in only one of the four populations. The numbers of pollen grains deposited per stigma varied from 0 to 60. The proportion of pollinated stigmas per flower ranged from 44% to 88% among populations and years. The numbers of pollen grains deposited per stigma and the percentages of pollinated stigmas were significantly different between populations, and two populations showed significant differences between years. A positive correlation between stigmatic pollen load and seed set was sought in ten population‐by‐year combinations but, in a given population, high stigmatic pollen loads did not always result in high seed set. Examination of pollen deposition, pistil and seed production over several sites and years showed that in addition to pollination, other factors such as resource or genetic loads were likely to limit the (lower than 10%) seed set in L. chinense. It appears that small, isolated populations experience severe pollination limitation; one population studied had seed/ovule ratios of 0.84% and 1.88% in 1995 and 1996. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society, 2002, 140 , 31–38.     

Microgametophyte population sizes and plant reproductive output in the insect-pollinated Prunella grandiflora (Lamiaceae)

Intraspecific variation in pollen deposition and number of pollen tubes per style is rarely quantified, but is essential for assessing the occurrence of pollen limitation and pollen competition and their evolutionary implications. Moreover, pollen deposition, pollen tube growth, and the fate of fertilized ovules are rarely distinguished in field studies. Here we present such a study in eight natural populations of Prunella grandiflora. We quantified microgametophyte population sizes and inferred pollen limitation when the number of fertilizable ovules exceeded pollen tubes, and assessed seed set and fate after open pollination. Two and three populations had on average significantly fewer pollen grains and pollen tubes per flower, respectively, than the fixed number of fertilizable ovules per fruit, while one population experienced significant pollen competition. Style length was positively correlated with the number of pollen tubes. While pollen availability was very variable, seed abortion was significantly less frequent in denser populations, and in one population the proportion of well-developed seeds was significantly, positively correlated with the number of pollen tubes in the style. Less pollen deposition, lower numbers of pollen tubes reaching the base of the style, lower pollen quality and therefore increased abortion of fertilized ovules can all reduce seed set in natural P. grandiflora stands. Substantial intraspecific variability implies that microgametophyte competition also occurs in this species. Finally, style morphology may affect pollen receipt.     

以杜鹃红山茶为母本的优良种间杂交父本筛选

以杜鹃红山茶(Camellia azalea)为母本,‘绿带可娜’、‘红芙蓉’、‘迪朱丽亚’等13个观赏性较强的山茶花品种为父本,采用常规杂交育种方法,共配置13个杂交组合进行杂交试验。以坐果率、结实率、出苗率、单花成苗率作为评价亲和性的指标对杂交父本进行筛选,利用因子分析法对杂交组合亲和力进行综合评价,并采用形态鉴定法比较杂交子代与父母本主要性状差异。结果表明,‘绿带可娜’、‘玛丽费丝’、‘尼丽夫人’、‘花露珍’、‘娃丽娜深’为亲和性高的父本,杜鹃红山茶ב绿带可娜’、杜鹃红山茶ב玛丽费丝’为杂交亲和性较高的组合。杜鹃红山茶种间杂交后代花色、花型表现趋于父本,叶片更接近于母本杜鹃红山茶,杂交后代均遗传母本全年开花的特性。     

Effects of pollination and pollen source on the seed set ofPedicularis palustris

Habitat alteration can deteriorate plant-pollinator interactions and thereby increase the risk of population extinction. As part of a larger study on the effects of changes in land use on fen grassland vegetation, factors influencing the seed set of a short-lived, endangered wetland plant,Pedicularis palustris, were studied. We conducted field pollination experiments in one large and one small population. To investigate the effect of pollen source on seed set, individual flowers of caged plants were left unpollinated or were pollinated with pollen from the same flower, the same population or another population. To study pollen limitation and flower display, whole plants were subjected to pollinator exclosure, hand pollination or natural pollination. Self-compatibility was high, but differed between populations (61% and 97% of seed set after cross-pollination within populations). Cross-pollination between populations did not significantly alter seed number per capsule. Pollinator exclosure resulted in a very low seed set (<15% of natural seed set), despite high self-compatibility. The most likely explanations for high self-compatibility in combination with low autofertility are geitonogamy as reproductive assurance, selective neutrality of self-compatibility and phylogenetic constraints. Because of low autofertility, the seed set inP. palustris depends on pollinators. In the study populations, natural pollination was clearly sufficient for maximum seed production per plant, but seed set per capsule was significantly pollen-limited in the smaller population. Plants in this population also had a higher maximum percentage of simultaneously open flowers than those of the large population (31% vs. 13%), while flower longevity was generally extended without pollination. It is concluded thatP. palustris may influence pollinator behaviour and therefore the risk of pollen limitation by flower display.P. palustris showed a flexible reaction to differing pollination regimes without losses in overall seed set in the study populations.     

Genetic composition and diploid hybrid speciation of a high mountain pine, Pinus densata, native to the Tibetan plateau

Pinus densata has been suggested to have originated from hybridization events involving P. tabulaeformis and P. yunnanensis. In this study, allozyme differentiation at 12 loci was studied in 14 populations of P. tabulaeformis, P. densata, and P. yunnanensis from China. The observed genetic composition of P. densata supported the hybrid hypothesis and showed varying degrees of contribution from P. yunnanensis and P. tabulaeformis among its populations. These data, together with previous chloroplast DNA results, indicated different evolutionary histories among P. densata populations. To examine the possibility of ongoing hybridization among the three species, we analyzed patterns of linkage disequilibria between allozyme loci in ovule, pollen, and zygote pools. None of these tests suggested that there is significant ongoing gene exchange, implying that populations of P. densata have a stabilized hybrid nature. The normal fertility and high fecundity of P. densata indicate that this hybrid is maintained through sexual reproduction. P. densata represents an example of diploid hybrid speciation in an extreme ecological habitat that is both spatially and ecologically separated from that of its parents.     

Does the morphological fit between flowers and pollinators affect pollen deposition? An experimental test in a buzz‐pollinated species with anther dimorphism

Some pollination systems, such as buzz‐pollination, are associated with floral morphologies that require a close physical interaction between floral sexual organs and insect visitors. In these systems, a pollinator's size relative to the flower may be an important feature determining whether the visitor touches both male and female sexual organs and thus transfers pollen between plants efficiently. To date, few studies have addressed whether in fact the “fit” between flower and pollinator influences pollen transfer, particularly among buzz‐pollinated species. Here we use Solanum rostratum, a buzz‐pollinated plant with dimorphic anthers and mirror‐image flowers, to investigate whether the morphological fit between the pollinator's body and floral morphology influences pollen deposition. We hypothesized that when the size of the pollinator matches the separation between the sexual organs in a flower, more pollen should be transferred to the stigma than when the visitor is either too small or too big relative to the flower. To test this hypothesis, we exposed flowers of S. rostratum with varying levels of separation between sexual organs, to bumblebees (Bombus terrestris) of different sizes. We recorded the number of visits received, pollen deposition, and fruit and seed production. We found higher pollen deposition when bees were the same size or bigger than the separation between anther and stigma within a flower. We found a similar, but not statistically significant pattern for fruit set. In contrast, seed set was more likely to occur when the size of the flower exceeded the size of the bee, suggesting that other postpollination processes may be important in translating pollen receipt to seed set. Our results suggest that the fit between flower and pollinator significantly influences pollen deposition in this buzz‐pollinated species. We speculate that in buzz‐pollinated species where floral morphology and pollinators interact closely, variation in the visitor's size may determine whether it acts mainly as a pollinator or as a pollen thief (i.e., removing pollen rewards but contributing little to pollen deposition and fertilization).     

Shifts to earlier selfing in sympatry may reduce costs of pollinator sharing

Coexisting plant congeners often experience strong competition for resources. Competition for pollinators can result in direct fitness costs via reduced seed set or indirect costs via heterospecific pollen transfer (HPT), causing subsequent gamete loss and unfit hybrid offspring production. Autonomous selfing may alleviate these costs, but to preempt HPT, selfing should occur early, before opportunities for HPT occur (i.e., “preemptive selfing hypothesis”). We evaluated conditions for this hypothesis in Collinsia sister species, C. linearis and C. rattanii. In field studies, we found virtually identical flowering times and pollinator sharing between congeners in sympatric populations. Compared to allopatric populations, sympatric C. linearis populations enjoyed higher pollinator visitation rates, whereas visitation to C. rattanii did not differ in sympatry. Importantly, the risk of HPT to each species in sympatry was strongly asymmetrical; interspecies visits comprised 40% of all flower‐to‐flower visits involving C. rattanii compared to just 4% involving C. linearis. Additionally, our greenhouse experiment demonstrated a strong cost of hybridization when C. rattanii was the pollen donor. Together, these results suggest that C. rattanii pays the greatest cost of pollinator sharing. Matching predictions of the preemptive selfing hypothesis, C. rattanii exhibit significantly earlier selfing in sympatric relative to allopatric populations.     

Effects of Tidal Action on Pollination and Reproductive Allocation in an Estuarine Emergent Wetland Plant–Sagittaria graminea (Alismataceae)

In estuarine wetlands, the daily periodic tidal activity has a profound effect on plant growth and reproduction. We studied the effects of tidal action on pollination and reproductive allocation of Sagittaria graminea. Results showed that the species had very different reproductive allocation in tidal and non-tidal habitats. In the tidal area, seed production was only 9.7% of that in non-tidal habitat, however, plants produced more male flowers and nearly twice the corms compared to those in non-tidal habitat. An experiment showed that the time available for effective pollination determined the pollination rate and pollen deposition in the tidal area. A control experiment suggested that low pollen deposition from low visitation frequency is not the main cause of very low seed sets or seed production in this plant in tidal habitat. The negative effects of tides (water) on pollen germination may surpass the influence of low pollen deposition from low visitation frequency. The length of time from pollen deposition to flower being submerged by water affected pollen germination rate on stigmas; more than three hours is necessary to allow pollen germination and complete fertilization to eliminate the risk of pollen grains being washed away by tidal water.     

CPDNA INHERITANCE IN INTERSPECIFIC CROSSES AND EVOLUTIONARY INFERENCE IN LOUISIANA IRISES

Inheritance of chloroplast DNA haplotypes was determined for progeny from interspecific crosses involving Iris fulva and Iris hexagona. Polymerase chain reaction amplification of chloroplast DNA followed by restriction fragment length analysis of the amplification products was used to identify the haplotypes of 213 experimental hybrids. This analysis allowed a test for maternal, paternal, and biparental inheritance in the hybrid offspring. Two of the hybrid progeny possessed haplotypes that were combinations of those present in the pollen and seed parents. One of the offspring possessed only the paternal haplotype. The remaining 210 plants had the haplotypes characteristic of the maternal plant. Chloroplast DNA variation in iris populations has previously been used to infer not only introgressive hybridization between I. fulva and I. hexagona, but also the greater role of direct pollen transfer relative to seed dispersal as the avenue for interspecific gene flow. We reexamined the previous conclusions concerning the mode of introgressive hybridization between I. fulva and I. hexagona in light of the results from the chloroplast DNA inheritance analysis. The low level of paternal and biparental inheritance detected in this analysis suggests that previous analyses using the chloroplast DNA as a seed-specific marker were robust. Furthermore, data concerning barriers to hybridization between I. fulva and I. hexagona suggest that the probability of chloroplast DNA introgression via pollen is low.     

The efficiency of insect pollination of the neophyte Impatiens glandulifera (Balsaminaceae)

To comprehend the reproductional success of Impatiens glandulifera in Central Europe, the pollination system was analyzed under field conditions. Impatiens glandulifera attracts a lot of visitors because of its abundant amount of nectar with its high sugar content. The range of visitors, their composition and their changes during the blooming time and their pollen loading capacity were investigated as well as plant and flower morphology, the nectar production, the quantity and viability of pollen, the stigmatic pollen load, the pollen/ovule ratio and the seed production of the neophyte. The visitors, which in Central Europe almost exclusively utilize the nectar, are passively covered with pollen because of the morphology and the mobile suspension of the flowers. Consequently the next landing results in a pollination of I. glandulifera during the female blooming phase. Although the germination rate of the pollen deposited on the stigma is very low, a 100% seed set is readily obtained during the initial visit to a flower in female stage.     

Pollination ecology of Penstemon roseus (Plantaginaceae), an endemic perennial shifted toward hummingbird specialization?

Summary Pink-flowered tubular Penstemon roseus (Plantaginaceae), which has shifted partially to hummingbird pollination, blooms on high-elevation slopes in the mountains in Tlaxcala, Mexico. We studied the interactions between pollinator visitation rates to flowers, pollen removal and deposition, flower size, and nectar removal frequency on seed production in P. roseus. We combine observational and experimental studies in two contrasting natural populations. Our manual pollinations revealed that P. roseus is fully self-compatible. Autonomous self- and manual self-pollinated flowers matured as many seeds as when outcrossed, but outcrossing seems to become better than selfing as the flowering season progressed. Early in the season flowers that were bagged and hand-selfed, hand-outcrossed, or autonomously selfed, or unbagged and naturally pollinated had equal seed set in all four treatments. But later in the season, outcross pollen gave approximately twice as much seed set as the two self-treatments. Low levels of pollen receipt and pollen removal were consistent with the long time elapsed for a given plant to be visited by hummingbirds, which suggests pollen shortage in both sites. Despite differences in pollinator visitation rates to flowers, probability of flower visitation, removal and deposition of pollen, and nectar production rates between populations, we found that total nectar production had no effect on seed production at either site. The daily nectar secretion rate of 0.3–0.65 mg sugar per flower per 1–3 days was low relative to other hummingbird-adapted Penstemon species (typical range: 1.5–5 mg sugar per flower), and it might be intermediate between hummingbird- and bee-adapted Penstemon flowers. Our results support the hypothesis about a shift toward hummingbird pollination, and provide an example of a ‘despecialized’ Penstemon species, which attracts high-energy pollinators (hummingbirds) and profits from outcrossing, but retains bee-syndrome floral traits and low sugar production rates.     

Flower morphology and pollinator dynamics in Solanum carolinense (Solanaceae): implications for the evolution of andromonoecy

Flower morphology and pollinator dynamics play an important role in the evolution and maintenance of many breeding systems, including andromonoecy. We used a series of field experiments to test the functional relationship between flower morphology and pollination dynamics (e.g., pollen receipt and export) in Solanum carolinense. We find that long-styled flowers serve primarily as pollen recipients and short-styled flowers as pollen donors, making this the first study to support the male-female interference hypothesis for the evolution of andromonoecy. However, this difference in the primary male or female function of the flowers depends on the pollinator identity. In flowers visited by Bombus impatiens, style length has a positive relationship with pollen deposition and a negative relationship with pollen removal. In contrast, neither morphological nor behavioral traits determine pollen deposition or removal by small halictid bees. We demonstrate that different pollinators could select for different floral morphologies, and thus, our research suggests that pollinator-specific interactions with flower morphology play an important role in the evolution and maintenance of anrdromonoecy.     

Hybridization between two polyploid Cardamine (Brassicaceae) species in North-western Spain: discordance between morphological and genetic variation patterns

BACKGROUND AND AIMS: Hybridization is an important evolutionary phenomenon, and therefore a detailed understanding of the dynamics of interspecific gene flow and resulting morphological and genetic patterns is of widespread interest. Here hybridization between the polyploids Cardamine pratensis and C. raphanifolia at four localities is explored. Using different types of data, the aim is to provide simultaneous and direct comparisons between genotype and phenotype variation patterns in the studied hybrid populations. METHODS: Evidence of hybridization has been gathered from morphology, molecular markers (amplified fragment length polymorphism and chloroplast DNA sequences), pollen viability, karyology and nuclear DNA content. KEY RESULTS: All data support extensive gene flow occurring in the hybrid populations. A wide range of morphological and genetic variation is observed, which includes both parental and intermediate types. Unbalanced pollen fertility and several ploidy levels are recorded. CONCLUSIONS: Incongruence reported between genotype and phenotype suggests that parental phenotypes are affected by introgression, and intermediate hybrid phenotypes can be genetically closer to one of the parents. Thus, it is evident that morphology, when used alone, can be misleading for interpreting hybridization, and critical evaluation of other data is needed.     

Comparative genetics of potential prezygotic and postzygotic isolating barriers in a Lycopersicon species cross

I compare the genetic basis of quantitative traits that potentially contribute to pre- and postzygotic isolation between the plant species Solanum lycopersicum (formerly Lycopersicon esculentum) and Solanum habrochaites (formerly Lycopersicon hirsutum), using quantitative trait loci (QTL) mapping in a set of near-isogenic lines. Putative prezygotic isolating traits include flower size, flower shape, stigma exertion, and inflorescence length, that can influence pollinator preferences and/or selfing rates, and therefore gene flow between divergent types. Postzygotic isolating traits are hybrid pollen and seed sterility. Three substantive results emerge from these analyses. First, the genetic basis of floral differentiation appears to be somewhat less complex than the genetic basis of postzygotic hybrid sterility, although these differences are very modest. Second, there is little evidence that traits for floral differentiation are causally or mechanistically associated with hybrid sterility traits in this species cross. Third, there is little evidence that hybrid sterility QTL are more frequently associated with chromosomal centromeric regions, in comparison to floral trait QTL, a prediction of centromeric drive models of hybrid sterility. Although genome-wide associations are not evident in this analysis, several individual chromosomal regions that contain clusters of QTL for both floral and sterility traits, or that indicate hybrid sterility effects at centromere locations, warrant further fine-scale investigation.     

Hybrids between cultivated and wild carrots in natural populations in Denmark

Many cultivated plant species are able to hybridize with related wild plants. However, it is not clear whether their hybrids are able to survive and reproduce outside managed fields, and if cultivar genes introgress into wild populations. In areas where wild carrots co-occur with carrot root-crops, pollen and seeds may flow from two different sources in the fields to the surrounding wild populations: from pure cultivar plants that occasionally flower, and from flowering 'bolters' that originate from hybridizations between wild (male) and cultivated carrots (female) in seed production fields in warmer regions of the world. To test whether hybrids are formed and survive in wild Danish populations, and whether prolonged hybridization has led to introgression of cultivar genes, we collected leaf material from adult individuals growing close to carrot fields and analysed their genotypic composition by AFLP. Four hybrids were identified among the 71 plants analysed, and these were most likely F(2) or backcross individuals, sired by pollen from hybrid bolters. Wild populations close to fields were genetically somewhat more similar to cultivars than wild populations far from fields, suggesting that neutral or beneficial cultivar alleles can introgress into the wild gene pool. Despite generations of improvement and adaptation of cultivar carrots to highly managed field conditions, hybrids can thus sometimes survive in wild populations close to carrot fields, and their genes transfer to wild populations by introgression.     

Female reproductive success in gynodioecious Thymus vulgaris: pollen versus nutrient limitation and pollinator foraging behaviour

Gynodioecy is a dimorphic breeding system in which female individuals coexist with hermaphroditic individuals in the same population. Females only contribute to the next generation via ovules, and many studies have shown that they are usually less attractive than hermaphrodites to pollinators. Several mechanisms have been proposed to explain how females manage to persist in populations despite these disadvantages. The ‘resource reallocation hypothesis’ (RRH) states that females channel resources not invested in pollen production and floral advertisement towards the production of more and/or larger seeds. We investigated pollination patterns and tested the RRH in a population of Thymus vulgaris. We measured flower display, flower size, nectar production, visitation rates, pollinator constancy and flower lifespan in the two morphs. In addition, we measured experimentally the effects of pollen and resource addition on female reproductive success (fruit set, seed set, seed weight) of the two morphs. Despite lower investment in floral advertisement, female individuals were no less attractive to pollinators than hermaphrodites on a per flower basis. Other measures of pollinator behaviour (number of flowers visited per plant, morph preference and morph constancy) also showed that pollinators did not discriminate against female flowers. In addition, stigma receptivity was longer in female flowers. Accordingly, and contrary to most studies on gynodioecious species, reproductive success of females was not pollen limited. Instead, seed production was pollen limited in hermaphrodites, suggesting low levels of cross‐pollination in hermaphrodites. Seed production was resource limited in hermaphrodites, but not in females, thus providing support for the RRH. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 175 , 395–408.     

CONSUMER DRIVEN POLLEN LIMITATION OF SEED PRODUCTION IN MARSH GRASSES

While flower predators can limit the sexual expression and seed production of salt marsh grasses, the relationship between these two effects of consumers has not been explored. At our study site, predation on Spartina patens, Spartina alterniflora, and Distichlis spicata was twice as high in 1985 (~70% ovule destruction) as in 1986 (~35% ovule destruction). In both years consumers destroyed flowers before maturity, reducing sexual expression, and particularly suppressed male sexual expression. Sexual suppression of males was much more pronounced in 1985 when flower predation was severe and the seed production of undamaged ovules was dramatically reduced. A number of lines of evidence suggest that predator limitation of male sexual expression and pollen supply contributed to low seed output in 1985. 1) Undamaged ovules of all three grasses protected from consumers but exposed to ambient windbome pollen set many more seeds in 1986 than in 1985, suggesting that pollen was more abundant in 1986; 2) Artificial pollinations revealed that marsh grasses are generally pollen-limited and that pollen limitation at our study site was more severe in 1985 than 1986; and 3) Caging stands of marsh grasses generally led to less predator damage, increased male densities and seed sets similar to those for hand-pollinated flowers. Our results support the hypothesis that flower predators can indirectly limit seed production by decreasing pollen availability.