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Flowers of Salvia are characterized by a diversity of staminal lever types mediating pollen transfer. In the East Asian subgenus Glutinaria, species have been categorized based on their distinct flower and stamen morphologies. A hypothesized advantage of degraded-lever types suggests they may optimize pollinator foraging time, increase visitation rates, and potentially trigger autonomous self-pollination. However, this hypothesis remains untested. Here, Salvia castanea, S. miltiorrhiza, and S. liguliloba were selected as test species representing the three major flower and stamen types of the East Asian sages. We compared the species with regard to their inflorescence architecture, floral display, nectar reward, pollinator efficiency, and seed set. We found that S. liguliloba had a degraded-lever type that significantly reduced pollinator foraging time did not significantly increase pollination efficiency. These species have a mixed mating pattern with high seed set, no pollen- or pollinator limitation, and no inbreeding depression. We conclude that the diversity of floral traits is addressed to pollinators, whereas reproductive success emerges from a complex interplay of factors encompassing floral characteristics, pollination efficiency, plant life history, or/and other biotic and abiotic factors. For this reason, the link between floral morphological traits and mating systems should not overestimated. [ABSTRACT FROM AUTHOR]

The escalation in the intensity, frequency, and duration of high-temperature (HT) stress is currently unparalleled, which aggravates the challenges for crop production. Yet, the stage-dependent responses of reproductive organs to HT stress at the morphological, physiological, and molecular levels remain inadequately explored in pivotal staple crops. This review synthesized current knowledge regarding the mechanisms by which HT stress induces abnormalities and aberrations in reproductive growth and development, as well as by which it alters the morphology and function of florets, flowering patterns, and the processes of pollination and fertilization in maize (Zea mays L.). We identified the stage-specific sensitivities to HT stress and accurately defined the sensitive period from a time scale of days to hours. The microspore tetrad phase of pollen development and anthesis (especially shortly after pollination) are most sensitive to HT stress, and even brief temperature spikes during these stages can lead to significant kernel loss. The impetuses behind the heat-induced impairments in seed set are closely related to carbon, reactive oxygen species, phytohormone signals, ion (e.g. Ca2+) homeostasis, plasma membrane structure and function, and others. Recent advances in understanding the genetic mechanisms underlying HT stress responses during maize sexual reproduction have been systematically summarized. [ABSTRACT FROM AUTHOR]

Premise of the study: On islands, flowering plants tend to be more generalist in their pollination needs, as insects (the main pollinators of flowering plants) are underrepresented in these ecosystems compared to the mainland. In addition, some vertebrate species that are typically insectivorous or granivorous on the mainland are forced to broaden their diet and consume other resources such as nectar or pollen on the islands. The shrub Malva arborea , with its large and colourful flowers, attracts different groups of potential pollinators. This study aimed to compare the effectiveness of vertebrates versus insects in an insular population of M. arborea and to investigate its reproductive system. Methods: For three groups of taxa (insects, birds and lizards), we assessed the two components of pollination effectiveness: (i) the quantitative component (i.e. number of visits and number of flowers contacted) through direct observations of flowers; and (ii) the qualitative component (fruit and seed set, number and size of seeds and proportion of seedling emergence) through pollinator exclusion experiments. Key results: Vertebrates (birds and lizards) were quantitatively the most effective pollinators, followed by insects. However, when all three groups visited the flowers, fruit and seed set were higher than when any of them were excluded. We also found that M. arborea has hermaphrodite flowers and is able to reproduce by autogamy, although less efficiently than when pollinated by animals. Conclusions: Both vertebrates and insects play an important role in the reproduction of M. arborea. Although the plant does not need pollinators to produce seeds, its reproductive success increases when all pollinators are allowed to visit the flowers. Besides providing new information on M. arborea, these findings may help to better understand the role of different pollinator groups in the reproduction of other plant species, especially on islands where the co-occurrence of vertebrate and invertebrate pollination in the same plant species is usual. [ABSTRACT FROM AUTHOR]

Numerous studies have identified traits associated with anther mimicry; however, the processes underlying floral deception remain poorly documented for these structures. We studied the importance of pollinator attraction and mechanical fit of anther mimics in Tritonia laxifolia (Iridaceae) and their relative contributions to reproductive success. To determine anther mimics role in attraction, we offered bees' binary choices to flowers painted with UV‐absorbent and UV‐reflecting paints. We also conducted preference experiments between flowers with excised anther mimics and unmanipulated controls, from which mechanical fit was assessed by allowing single visits. Anther mimics' effects on female reproductive success were determined using similar treatments, but on rooted plants. Bees preferred UV‐absorbent over UV‐reflecting anther mimics. Bees did not discriminate between flowers with and without three‐dimensional anther mimics. Single visits resulted in more pollen deposition on unmanipulated controls over flowers with their anther mimics excised, which was directly linked to pollen‐collecting behavior. Controls with unmanipulated anther mimics had higher seed set than those with their anther mimics excised. This study provides insights into pollinator‐mediated selection on deceptive floral signals and shows that three‐dimensional anther mimics increases reproductive success through both attraction and pollen‐collecting behaviors. [ABSTRACT FROM AUTHOR]

High reproductive assurance is regarded as a key advantage of uniparentally reproducing organisms for establishing a new population. This demographic benefit should especially be relevant for plants with autonomous apomixis, that is those which produce seeds completely independently from mates and pollinators. Indeed, many autonomous apomicts occupy larger distributional ranges when compared to their sexual relatives, showing geographical parthenogenesis patterns. However, uniparental reproduction advantage has only rarely been quantified in natural populations and results provided a mixed support, partly because allopatric sexual and asexual populations were exposed to different environmental and pollination conditions causing considerable between‐population variation in the level of reproductive assurance. Here, we compared the level and stability of reproductive assurance between sexual self‐incompatible and asexual autonomously apomictic plants of Hieracium alpinum (Asteraceae) cultivated in a sympatric low‐density population with two levels of spatial clumping of sexual plants. Overall, we found that the realized seed set (i.e. proportion of well‐developed seeds per capitulum) of asexuals was ca. 3 times greater than that of sexuals (83% vs. 27%), whereas the variance of this trait expressed as coefficient of variation was ca. 4 times smaller in asexuals compared with sexuals (19% vs. 83%). Solitary sexual plants had more than 2 times lower realized seed set when compared to clumps composed of two spatially close (20–30 cm) sexual plants (13% vs. 34%). Our study provides experimental evidence for benefit of uniparental reproduction of asexuals in a sympatric situation when the availability of mates is limited. This, together with unpredictability of pollinator environment could provide autonomous apomicts with an ultimate demographic superiority during colonization reflected in geographical parthenogenesis observed in this species. [ABSTRACT FROM AUTHOR]

Researchers have long assumed that plant spatial location influences plant reproductive success and pollinator foraging behaviour. For example, many flowering plant populations have small, linear or irregular shapes that increase the proportion of plants on the edge, which may reduce mating opportunities through both male and female function. Additionally, plants that rely on pollinators may be particularly vulnerable to edge effects if those pollinators exhibit restricted foraging and pollen carryover is limited. To explore the effects of spatial location (edge vs. interior) on siring success, seed production, pollinator foraging patterns and pollen-mediated gene dispersal, we established a square experimental array of 49 Mimulus ringens (monkeyflower) plants. We observed foraging patterns of pollinating bumblebees and used paternity analysis to quantify male and female reproductive success and mate diversity for plants on the edge versus interior. We found no significant differences between edge and interior plants in the number of seeds sired, mothered or the number of sires per fruit. However, we found strong differences in pollinator behaviour based on plant location, including 15 % lower per flower visitation rates and substantially longer interplant moves for edge plants. This translated into 40 % greater pollen-mediated gene dispersal for edge than for interior plants. Overall, our results suggest that edge effects are not as strong as is commonly assumed, and that different plant reproduction parameters respond to spatial location independently. [ABSTRACT FROM AUTHOR]

Climate change-induced increases in the frequency of extreme weather events, particularly heatwaves, are a serious threat to crop productivity. The productivity of grain crops is dependent on the success of sexual reproduction, which is very sensitive to heat stress. Male gametophyte development has been identified as the most heat-vulnerable stage. This review outlines the susceptibility of the various stages of sexual reproduction in flowering plants from the time of floral transition to double fertilization. We summarize current knowledge concerning the molecular mechanisms underpinning the heat stress-induced aberrations and abnormalities at flowering, male reproductive development, female reproductive development, and fertilization. We highlight the stage-specific bottlenecks in sexual reproduction, which regulate seed set and final yields under high-temperature conditions, together with the outstanding research questions concerning genotypic and species-specific differences in thermotolerance observed in crops. This knowledge is essential for trait selection and genetic modification strategies for the development of heat-tolerant genotypes and high-temperature-resilient crops. [ABSTRACT FROM AUTHOR]

Fragmentation of plant communities is generally considered to be detrimental to the survival of the constituent species, especially those that are rare. We investigated the effects of fragmentation on reproductive biology in nine populations of the rare taxon Banksia nivea subsp. uliginosa , differing in size and habitat context. Small mammals were the main pollinator, with lower contributions from honeybees and birds (honeyeaters). There was no significant relationship between population size, fruit set and seed germinability. Fruit set was marginally highest (25.5 ± 3.4) in medium size populations and was variable over years. Lower fruit set (1.0 ± 0.6) in the smallest population may be due to inbreeding depression or lack of pollinators in a degraded habitat, but low fruit set was also observed in the largest population despite high levels of gene flow, possibly due to low pollinator visitation rate in a low-density population. Seeds from all populations had high germination success (>93.4%). Predation occurred in up to 56% of fruit and increased with increasing population size, but was not significantly different between populations of different size. Our study provided evidence that the reproductive output in species in a naturally fragmented landscape system may be resilient to reduced population size and other influences of anthropogenic fragmentation. [ABSTRACT FROM AUTHOR]

Transitions from self‐incompatibility to self‐compatibility in angiosperms may be frequently driven by selection for reproductive assurance when mates or pollinators are rare, and are often succeeded by loss of inbreeding depression by purging. Here, we use experimental evolution to investigate the spread of self‐compatibility from one such population of the perennial plant Linaria cavanillesii into self‐incompatible (SI) populations that still have high inbreeding depression. We introduced self‐compatible (SC) individuals at different frequencies into replicate experimental populations of L. cavanillesii that varied in access to pollinators. Our experiment revealed a rapid shift to self‐compatibility in all replicates, driven by both greater seed set and greater outcross siring success of SC individuals. We discuss our results in the light of computer simulations that confirm the tendency of self‐compatibility to spread into SI populations under the observed conditions. Our study illustrates the ease with which self‐compatibility can spread among populations, a requisite for species‐wide transitions from self‐incompatibility to self‐compatibility. [ABSTRACT FROM AUTHOR]

Flowers visited by a broad assemblage of animals may nevertheless be considered to have a specialized pollination system if pollen deposition is effected mainly by a subset of these visitors. The importance of a particular animal group for pollination derives mainly from the relative rate of floral visitation and per-visit effectiveness for pollen deposition. We assessed the relative importance of birds and insects for pollination of the African shrub Syncolostemon densiflorus (Lamiaceae). Flower visitors were observed to evaluate their visitation rates. Virgin flowers were exposed to single visits by nine animal visitor groups to evaluate their effectiveness at depositing pollen on stigmas. We selectively excluded birds and larger insects from flowers to assess the contribution of smaller visitors to pollen deposition and seed set. Sunbirds and insects visited flowers at a similar frequency, but on a per-visit basis, sunbirds deposited more pollen on stigmas than did any of the insect groups, including honeybees, long-proboscid flies, butterflies and day-flying hawkmoths. Selective exclusion of birds and larger insects resulted in a large decline in pollen deposition on stigmas and seed production. These results show that S. densiflorus is pollinated mainly by sunbirds, despite its attraction of a broad assemblage of insect flower visitors. These findings highlight the importance of per-visit pollination effectiveness and selective exclusion for understanding the ecological importance of different flower visitors. [ABSTRACT FROM AUTHOR]

Conifers' exceptionally large genome (20-30 Gb) is scattered with 60% retrotransposon (RT) components and we have little knowledge on their origin and evolutionary implications. RTs may impede the expression of flanking genes and provide sources of the formation of novel small RNA (sRNAs) populations to constrain events of transposon (TE) proliferation/transposition. Here we show a declining expression of 24-nt-long sRNAs and low expression levels of their key processing gene, pgRTL2 (RNASE THREE LIKE 2) at seed set in Picea glauca. The sRNAs in 24-nt size class are significantly less enriched in type and read number than 21-nt sRNAs and have not been documented in other species. The architecture of MIR loci generating highly expressed 24-/21-nt sRNAs is featured by long terminal repeat-retrotransposons (LTR-RTs) in families of Ty3/Gypsy and Ty1/Copia elements. This implies that the production of sRNAs may be predominantly originated from TE fragments on chromosomes. Furthermore, a large proportion of highly expressed 24-nt sRNAs does not have predictable targets against unique genes in Picea, suggestive of their potential pathway in DNA methylation modifications on, for instance, TEs. Additionally, the classification of computationally predicted sRNAs suggests that 24-nt sRNA targets may bear particular functions inmetabolic processes while 21-nt sRNAs target genes involved inmany different biological processes. This study, therefore, directs our attention to a possible extrapolation that lacking of 24-nt sRNAs at the late conifer seed developmental phase may result in less constraints in TE activities, thus contributing to the massive expansion of genome size. [ABSTRACT FROM AUTHOR]

Background and Aims Most pollinators are generalists and therefore are likely to transfer heterospecific pollen among co-flowering plants. Most work on the impacts of heterospecific pollen deposition on plant fecundity has utilized hand-pollination experiments in greenhouse settings, and we continue to know very little about the reproductive effects of heterospecific pollen in field settings. Methods We explored how patterns of naturally deposited heterospecific pollen relate to the reproductive output of Delphinium barbeyi, a common subalpine perennial herb in the Rocky Mountains (USA). We assessed a wide range of naturally occurring heterospecific pollen proportions and pollen load sizes, and linked stigmatic pollen deposition directly to seed set in individual carpels in the field. Key Results We found that heterospecific pollen deposition in D. barbeyi is common, but typically found at low levels across stigmas collected in our sites. Neither conspecific nor heterospecific pollen deposition was related to carpel abortion. By contrast, we saw a significant positive relationship between conspecific pollen amount and viable seed production, as well as a significant negative interaction between the effects of conspecific pollen and heterospecific pollen amount, whereby the effect of conspecific pollen on viable seed production became weaker with greater heterospecific deposition on stigmas. Conclusions To our knowledge, this is the first demonstration of a relationship between heterospecific pollen and seed production in a field setting. In addition, it is the first report of an interaction between conspecific and heterospecific pollen quantities on seed production. These findings, taken with the results from other studies, suggest that greenhouse hand-pollination studies and field studies should be more tightly integrated in future work to better understand how heterospecific pollen transfer can be detrimental for plant reproduction. [ABSTRACT FROM AUTHOR]

Floral morphology, nectar secretion strategies and the contribution of pollinators to the reproductive success of plants provide important clues regarding the levels of generalization or specialization in pollination systems. Anthesis throughout the day and night allows flowers to be visited by diurnal and nocturnal pollinators, promoting generalization or specialization. We studied three species in the diverse tropical genus Inga to: (1) quantify the response of flowers to successive nectar extractions and (2) determine the contribution of diurnal and nocturnal floral visitors to female reproductive success. Inga flowers could be clearly distinguished mainly on the basis of the staminal tube diameter and the quantities of filaments and pollen grains. Successive nectar removals led to a decrease of 60% in the total nectar secretion in I. vera and to increases of 20% in I. ingoides and 10% in I. striata. Despite these differences, the studied Inga spp. exhibited similar patterns of visitation rates and shared diurnal and nocturnal pollinators. Nocturnal pollinators contributed ten times more than diurnal pollinators to the female reproductive success of Inga. Floral morphology, nectar secretion patterns and pollination ecology data suggest an evolutionary trend towards specialization for nocturnal pollinators in Inga spp. with crepuscular or nocturnal flowers. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177, 230-245. [ABSTRACT FROM AUTHOR]

Potential decreases in crop yield from reductions in bee-mediated pollination services threaten food production demands of a growing population. Many fruit and vegetable growers supplement their fields with bee colonies during crop bloom. The extent to which crop production requires supplementary pollination services beyond those provided by wild bees is not well documented. Pumpkin, Cucurbita pepo L., requires bee-mediated pollination for fruit development. Previous research identified the common eastern bumble bee, Bombus impatiens (Cresson), as the most efficient pumpkin pollinator. Two concomitant studies were conducted to examine pollination deficits in NewYork pumpkin fields from 2011 to 2013. In the first study, fruit weight, seed set, and B. impatiens visits to pumpkin flowers were compared across fields supplemented with B. impatiens colonies at a recommended stocking density of five colonies per hectare, a high density of 15 colonies per hectare, or not supplemented with bees. In the second study, fruit weight and seed set of pumpkins that received supplemental pollen through hand-pollination were compared with those that were openpollinated by wild bees. Results indicated that supplementing pumpkin fields with B. impatiens colonies, regardless of stocking density, did not increase fruit weight, seed set, or B. impatiens visits to pumpkin flowers. Fruit weight and seed set did not differ between hand- and open-pollinated treatments. In general, we conclude that pumpkin production in central New York is not limited by inadequate pollination services provided by wild bees and that on average, supplementation with B. impatiens colonies did not improve pumpkin yield. [ABSTRACT FROM AUTHOR]

Outcrossing rates and seed set were estimated at both the population and individual plant scale within four populations of Xanthorrhoea johnsonii. Sites differed with respect to habitat disturbance (time since fire), plant density, mean plant height, and mean inflorescence length. Allozyme data from progeny arrays of 24 seeds per plant from ten plants at each site were used to determine maternal outcrossing rates, which were found to be consistently high at all sites (> 90%). Small but significant levels of inbreeding were recorded at three of the four sites. There was close agreement between tm and ts measures, which indicated that most inbreeding was a result of within plant selfing rather than biparental inbreeding. Outcrossing rates were estimated within top, middle, and bottom thirds of spikes on six plants at a fifth site. Significant differences from complete outcrossing were recorded in the middle and/or bottom sections of three plants. Total seed set per plant and seed set per flower varied significantly among the four sites. Xanthorrhoea johnsonii appears to be able to maintain relatively high outcrossing rates under different ecological conditions, although levels of both seed set per plant and seed set per flower are much more variable. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110, 335-345. [ABSTRACT FROM AUTHOR]

Background and Aims The combination of clonality and a mating system promoting outcrossing is considered advantageous because outcrossing avoids the fitness costs of selfing within clones (geitonogamy) while clonality assures local persistence and increases floral display. The spatial spread of genetically identical plants (ramets) may, however, also decrease paternal diversity (the number of sires fertilizing a given dam) and fertility, particularly towards the centre of large clumped clones. This study aimed to quantify the impact of extensive clonal growth on fine-scale paternity patterns in a population of the allogamous Convallaria majalis. Methods A full analysis of paternity was performed by genotyping all flowering individuals and all viable seeds produced during a single season using AFLP. Mating patterns were examined and the spatial position of ramets was related to the extent of multiple paternity, fruiting success and seed production. Key Results The overall outcrossing rate was high (91 %) and pollen flow into the population was considerable (27 %). Despite extensive clonal growth, multiple paternity was relatively common (the fraction of siblings sharing the same father was 0·53 within ramets). The diversity of offspring collected from reproductive ramets surrounded by genetically identical inflorescences was as high as among offspring collected from ramets surrounded by distinct genets. There was no significant relationship between the similarity of the pollen load received by two ramets and the distance between them. Neither the distance of ramets with respect to distinct genets nor the distance to the genet centre significantly affected fruiting success or seed production. Conclusions Random mating and considerable pollen inflow most probably implied that pollen dispersal distances were sufficiently high to mitigate local mate scarcity despite extensive clonal spread. The data provide no evidence for the intrusion of clonal growth on fine-scale plant mating patterns. [ABSTRACT FROM PUBLISHER]

The reproductive (gametophytic) phase in flowering plants is often highly sensitive to hot or cold temperature stresses, with even a single hot day or cold night sometimes being fatal to reproductive success. This review describes studies of temperature stress on several crop plants, which suggest that pollen development and fertilization may often be the most sensitive reproductive stage. Transcriptome and proteomic studies on several plant species are beginning to identify stress response pathways that function during pollen development. An example is provided here of genotypic differences in the reproductive stress tolerance between two ecotypes of Arabidopsis thaliana Columbia (Col) and Hilversum (Hi-0), when reproducing under conditions of hot days and cold nights. Hi-0 exhibited a more severe reduction in seed set, correlated with a reduction in pollen tube growth potential and tropism defects. Hi-0 thus provides an Arabidopsis model to investigate strategies for improved stress tolerance in pollen. Understanding how different plants cope with stress during reproductive development offers the potential to identify genetic traits that could be manipulated to improve temperature tolerance in selected crop species being cultivated in marginal climates. [ABSTRACT FROM PUBLISHER]

The genus Scalesia is endemic to the Galápagos Islands. Scalesia cordata is a tree occurring only in the southern part of Isabela as small, remnant populations of larger forests. We studied the reproductive ecology of a population protected in an enclosure in order to reveal the extent to which the reproductive system limits the recruitment of young individuals. Pollinator observations revealed that each capitulum received, on average, 2.5 visits per hour and exposed receptive stigmas received many pollen grains. Even so, the seed set and recruitment of trees was poor. Crossing experiments showed that S. cordata produced about twice as many fertile seeds after outcrossing than after selfing. In addition, self-pollinated capitula flowered for a longer time than outcrossed capitula (3.8 ± 1.1 days vs. 2.1 ± 0.8 days). These results may suggest that the species is partly self-incompatible, as other species of the genus. The small population size, with its potential derived consequences, is most certainly a prominent threat to S. cordata. The pressure from introduced plant species found in the enclosure also contributes to the seemingly poor condition of the population. To recover S. cordata, we suggest enlarging the enclosure, removing the introduced plant species and continuing to cultivate plants as a genetic reserve. Introducing new genetic material is likely to increase the seed set of the population. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 162, 496–503. [ABSTRACT FROM AUTHOR]

The scientific work recorded by Darwin in his book on the cross- and self-fertilization of plants is an exemplar of interesting choices, careful technique, decades of work and methodical analyses that provided a plethora of robust results. The conclusions Darwin drew from his studies are, for the most part, valid and still relevant today. They focus primarily on providing data to support Darwin's hypothesis about the nature and importance of the benefits derived from cross-fertilization, although he conceded that a few plants seem to be invariably self-fertilized. The work is also a significant forerunner for the concepts of hybrid vigour and inbreeding depression. A wealth of information relating to flowers, flowering time, pollen efficacy, the results of cross- and self-pollination, the behaviour and impact of insects, seed and seed germination and plant breeding systems is scattered throughout the book. Darwin also related this book to several others he wrote in which some of these topics are included. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 161, 357–395. [ABSTRACT FROM AUTHOR]

As most plants of the Mediterranean region bloom in spring, there have been few studies of the reproductive biology of species with autumn–winter flowering. In this study, we investigate the breeding system of Anagyris foetida, one of the few shrubs that blooms at this time. The floral, phenological, and reproductive aspects of two populations of this Mediterranean legume from south-west Spain were studied via field and laboratory experiments. The variability of fruit and seeds was studied in another 12 Iberian populations with respect to certain meteorological parameters (temperature and rainfall). Anagyris foetida shows cauliflory, marked floral longevity, and adichogamy. The peak of flowering is in January–February. It is self-compatible, with no clear advantage of cross- over self-pollination, and with virtually no autonomous self-pollination. This is because the stigma, like some other legumes, prevents the germination of pollen if its surface is not ruptured by pollinators. The number of seeds per fruit under natural pollination was positively correlated with the total rainfall during the fruiting period (from January to May), and significantly influenced the percentage of fruit weight represented by the pericarp, in the sense that the smaller the number of viable seeds in the fruit, the greater the percentage of pericarp weight. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157, 519–532. [ABSTRACT FROM AUTHOR]

The reproductive success of Arum italicum in south-western France showed a positive relationship with plant vigour at both the plant (number of inflorescences) and inflorescence (number of seeds) levels. However, the infructescence and berry numbers were not related to the number of inflorescences, and two-fold more seeds were produced by individuals flowering several times than by those flowering just once. Moreover, the reproductive success of this species appeared to be limited by the high abortion rate (50%), strong predation pressure on the inflorescences (34%), and low seed set rate of nonpredated inflorescences (36%), suggesting pollination limitation. Nevertheless, a positive relationship was found between the mean number of Psychoda trapped per inflorescence and the number of maturing infructescences, particularly for the most abundant species, Psychoda crassipenis. Therefore, pollinator availability appeared to be an important limiting factor for fructification in the studied population, by contrast with other studies in which the fruit set appeared to be related more strongly to the density of inflorescences. Such different results may have been caused by the relatively low abundance of Psychoda in the present study. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 156, 43–49. [ABSTRACT FROM AUTHOR]

Determining the mechanisms governing sex-ratio variation in dioecious organisrns represents a central problem in evolutionary biology. It has been proposed that in plants with sex chromosomes competition between pollen tubes of female- versus male-determining microgametophytes (certation) causes female-biased primary sex ratios. Experimental support for this hypothesis is limited and recent workers have cast doubt on whether pollen-tube competition can modify sex ratios in dioecious plants. Here we investigate the influence of variation in pollination intensity on sex ratios in Rumex nivalis, a wind-pollinated alpine herb with strongly female-biased sex ratios. In a garden experiment, we experimentally manipulated pollination intensity using three concentric rings of female recipient plants at different distances from a central group of male pollen donors. This design enabled us to test the hypothesis that increasing pollen load size, by intensifying gametophyte competition, promotes female-biased sex ratios in R. nivalis. We detected a significant decline in pollen load at successive distance classes with concomitant reductions in seed set. Sex ratios of progeny were always female biased, but plants at the closest distance to male donors exhibited significantly greater female bias than more distant plants. The amount of female bias was positively correlated with the seed set of inflorescences. Hand pollination of stigmas resulted in ~ 100-fold higher stigmatic pollen loads than wind-pollinated stigmas and produced exceptionally female-biased progenies (female frequency = 0.96). Our results are the first to demonstrate a functional relation between stigmatic pollen capture, seed set, and sex ratio and suggest that certation can contribute towards female-biased sex ratios in dioecious plants. [ABSTRACT FROM AUTHOR]

• Background and Aims Pollen limitation is a significant determinant of seed production, and can result from both insufficient pollen quantity (pollen shortage) and quality (mainly relating to self-pollination). For animal-pollinated tree species with large floral displays, pollen limitation may be determined by a balance between increased pollen quantity due to increased attractiveness for pollinators, countered by increased self-pollination due to increased geitonogamy. The contributions of pollen shortage and self-pollination on seed production were quantitatively examined in the natural pollination of an insect-pollinated, dichogamous, endangered tree, Magnolia stellata, which has a large, showy floral display.• Methods Manual self- and cross-pollinations were conducted to determine the effects of selfing on seed production. The outcrossing rate was measured using microsatellite analyses of open-pollinated seeds, and the embryo mortality rate caused by self-pollination was indirectly estimated. The frequency of ovule mortality due to pollen shortage was also inferred using the embryo mortality and ovule survival rates from natural pollination.• Key Results The average fruit set, seed set per fruit, and ovule survival rate per tree from hand cross-pollination were 1·37, 3·15, and 3·34 times higher than those from hand self-pollination, respectively, indicating that self-pollination causes inbreeding depression for fruit and seed set. The multilocus-outcrossing rate (tm) was intermediate, 0·632, and the primary selfing rate was 0·657. This indicates that frequent geitonogamous selfing occurs. The ovule mortality rate due to pollen shortage and the embryo mortality rate due to self-pollination were estimated to be 80·8 % and 45·9 %, respectively.• Conclusions It is concluded that seed production of M. stellata is strongly limited by both pollen shortage and self-pollination. Inefficient beetle-pollination and the automimicry system via asynchronous flowering might be responsible for the high level of pollen shortage and frequent geitonogamy. This is despite a large, showy floral display and the dichogamous system of the species. [ABSTRACT FROM AUTHOR]

Prompted by the sparse knowledge of the reproductive biology of carnivorous plants, compared with studies of their trapping habits, we investigated the flowering phenology and pollination biology ofDrosera anglicaHuds. in two fens in mid-western Canada. Seed set and germination were used to compare the effectiveness of a series of pollination treatments, including single insect visits to virgin flowers. Flowers opened during mid-morning but closed by early afternoon, and exhibited pseudo-cleistogamic behaviour in cool, overcast weather.D. anglicawas found to be self-compatible, and able to self-pollinate and self-fertilize. Geitonogamy was an uncommon mode of self-reproduction because plants typically possessed a lone inflorescence upon which a single, short-lived flower opened, a few days before the next bud reached anthesis. Insect visits to the fragrance-lacking, nectarless flowers, chiefly by flies (Diptera: Syrphidae), were infrequent (one visit per 1 h 40 min of observation), and the low frequency of seed set and low numbers of seeds per fruit in pollination treatments involving insects, suggest the species does not rely on insects to effect pollination. Self-pollination, with or without the aid of a vector (insects, wind) was as effective as natural pollination; ultimately, autogamy is chiefly responsible for natural seed set. Thus, the species exhibits characteristics of facultative autogamy. © 2005 The Linnean Society of London,Botanical Journal of the Linnean Society, 2005,147, 417–426. [ABSTRACT FROM AUTHOR]

• Background and Aims It has been claimed that ovules linearly ordered within a fruit differ in their probabilities of reaching maturity. This was investigated by studying the effect the position of an ovule within the pod has on seed abortion and seed production in Bauhinia ungulata. [ABSTRACT FROM PUBLISHER]

Tylosema esculentum is a long‐lived perennial species endemic to arid areas of southern Africa. Its potential as a crop species has long been recognized as a result of the high oil and protein content of its seeds. The reproductive biology and breeding systems of the species were investigated in wild and experimental populations growing in Botswana. Field observations confirmed that the species is heterostylous with the pistil and anthers exhibiting reciprocal heights in the two morphs, although pollen size and sculpturing do not vary. The wet, non‐papillate stigma characteristic of the species is the first to be reported in the Caesalpinioideae. In vivo and in vitro diallel crossing experiments demonstrated that a diallelic self‐incompatability system exists in T. esculentum. The major site of pollen tube inhibition in the intramorph crosses was found to be in the style. This is the first report of functional heterostyly in the Fabaceae and of a confirmed self‐incompatibility system in the Caesalpinioideae. Three separate lines of evidence, the monitoring of fruit development in open‐pollinated plants, fruit set in diallel crossing experiments, and observations made in wild populations, demonstrated that fruit set and, by implication, seed set, are very low in this species. Floral abscission was a major limitation to the production of mature pods but there were also significant losses at other developmental stages of fruit production. The results suggest that low seed set may be an adaptation of the species to an environment in which rainfall is scarce. [ABSTRACT FROM PUBLISHER]

Herkogamy, the spatial separation of sex organs in hermaphroditic plants, has been proposed as a mechanism to reduce self-pollination and the associated processes of inbreeding and gamete wastage. Longitudinal herkogamy is the most frequent type, with two subtypes: approach herkogamy (anthers below the stigma), which is associated with diverse pollinator arrays, and reverse herkogamy (anthers above the stigma), associated with specialized, long-tongued pollinators. By using a herkogamy index that varied continuously from negative (reverse herkogamy) to positive (approach herkogamy) values, we studied the effect of continuous variation in herkogamy on pollinator attraction, selfing capability and plant fitness across three populations of Lonicera implexa differing in the relative abundance of long-tongued vs. short-tongued pollinators. Reverse herkogamy was significantly more frequent in the population where long-tongued pollinators were dominant than in the other two populations. Agreeing with this, the main floral visitors of L. implexa individuals with small and large herkogamy index were, respectively, long-tongued and short-tongued pollinators. Spontaneous selfing was low and increased with increasing herkogamy index (i.e. with approach herkogamy), although most of it occurred when there was close distance between anthers and stigma. Fruit production was unrelated to the herkogamy index in the population with long-tongued pollinators, but it increased with approach herkogamy (higher herkogamy index) in the other two populations. In contrast, seeds of individuals with reverse herkogamy (smaller herkogamy indices) germinated better. In this species, continuous variation in herkogamy might function as a reproductive strategy, as different morphotypes might be favoured by different pollinator assemblages. [ABSTRACT FROM AUTHOR]

To assess the potential of the indigenous syrphid fly Eristalis tenax (L.) as a pollinator of greenhouse sweet pepper, Capsicum annuum L., in southern Quebec, flowers of the `Bell Boy' cultivar were submitted to 1 of the following 3 treatments: (1) no exposure to flies; (2) exposure to a restricted number of visits by flies; and (3) unrestrained exposure to flies during floral receptivity. Fruits from both fly-visited groups produced larger seed sets than those of the nonvisited group, representing an augmentation of 9.2 and 19.3% in the limitedand unlimited visitation treatments, respectively. The number of visits per flower did not affect seed setting significantly, but an increase in the total duration of visits resulted in larger seed sets. E.tenax thus possesses desirable attributes for the pollination of sweet pepper under greenhouse conditions. [ABSTRACT FROM AUTHOR]