Stigma Height Research Articles

Unlocking the secrets of parasitic plants: A comparative study of the development and floral morphoanatomy of Pholisma (Lennoaceae)

Pholisma belongs to the family Lennoaceae, classified as obligate root holoparasites. Most existing studies are limited to addressing only P. arenarium. In this study, morphoanatomical and developmental aspects of flowers of the three species comprising Pholisma are described using histological embedding techniques in Paraplast and LR- White and observations by light microscopy and scanning electron microscopy. Similarities found in the three species include the presence of trichomes on the sepals, each carpel folding independently. Each carpel has transmitting tissue, and an empty cavity is distinguished in the centre of the style. The stigma is crateriform and of the wet type. Sporogenesis, gametogenesis, and floral development follow a similar pattern in the three species. Differences among species include the position of the stamens, pollen morphology, type of inflorescence, and colour of flowers and inflorescences. In P. arenarium, the stamens are located below the stigma height, and the pollen is tetracolporate and psilate; in P. sonorae, the stamens are at the same height as the stigma, and the pollen is tricolporate and reticulate; and in P. culiacana, the stamens are above the stigma height, and the pollen is tricolporate and psilate. The inflorescences in both P. arenarium and P. sonorae are cymes; the corolla colour is white with purple lines extending from the limb to the corolla tube. In contrast, the inflorescence in P. culiacana is a capitulum type, and the corolla colour is white with pink margins. The characters found in the three species of Pholisma are compared with some genera comprising the family Ehretiaceae.

Community-wide patterns in pollen and ovule production, their ratio (P/O), and other floral traits along an elevation gradient in southwestern China

BackgroundAs the male and female gametophytes of flowering plants, pollen and ovules largely determine the upper and lower boundaries of plant reproductive success. It is commonly predicted that pollen and ovule number per flower should increase, and pollen-ovule ratio (P/O) per flower should decrease with increasing elevation in response to a more stochastic pollination environment. Here, we aimed to determine the response of pollen number, ovule number, and P/O to other floral traits and elevation gradients for 84 insect-pollinated herbaceous flowering plant species in five sub-alpine and alpine communities (2709 to 3896 m a.s.l.) on Yulong Snow Mountain, southwestern China.ResultsSix floral traits, including P/O, floral display area, flower number, tube depth, flower shape, and pollen presentation, were highly correlated with pollen and ovule number per flower. With increasing elevation, pollen number and P/O per flower increased marginally and significantly, respectively; ovule number per individual, flower number per individual, stigma stamen separation, and inflorescence height decreased significantly. However, ovule number per flower and other floral traits (i.e., floral display area, tube depth, stigma height, stamen height, and pollen and P/O per individual) did not change with elevation. We detected significant phylogenetic signals for pollen number, ovule number, and P/O, suggesting that these traits may be highly conserved and with limited response to changing environmental conditions.ConclusionsResults revealed patterns of plant reproductive character evolution along elevation gradients and the potential factors governing their spatial variation in high-elevation environments. Plant species at high elevations are more likely adapted to cross-pollination, indicated by increased P/O per flower at high elevations on Yulong Mountain. Combined effects of phylogenetic history and plant-pollinator interactions should determine plant trait evolution.

Pollinator Proboscis Length Plays a Key Role in Floral Integration of Honeysuckle Flowers (Lonicera spp.).

Pollinator-mediated selection is supposed to influence floral integration. However, the potential pathway through which pollinators drive floral integration needs further investigations. We propose that pollinator proboscis length may play a key role in the evolution of floral integration. We first assessed the divergence of floral traits in 11 Lonicera species. Further, we detected the influence of pollinator proboscis length and eight floral traits on floral integration. We then used phylogenetic structural equation models (PSEMs) to illustrate the pathway through which pollinators drive the divergence of floral integration. Results of PCA indicated that species significantly differed in floral traits. Floral integration increased along with corolla tube length, stigma height, lip length, and the main pollinators' proboscis length. PSEMs revealed a potential pathway by which pollinator proboscis length directly selected on corolla tube length and stigma height, while lip length co-varied with stigma height. Compared to species with short corolla tubes, long-tube flowers may experience more intense pollinator-mediated selection due to more specialized pollination systems and thus reduce variation in the floral traits. Along elongation of corolla tube and stigma height, the covariation of other relevant traits might help to maintain pollination success. The direct and indirect pollinator-mediation selection collectively enhances floral integration.

Intra-individual floral variation improves male fitness in a hummingbird-pollinated species

Intra-individual variation in floral traits is widespread but yet poorly understood. Variations in flower size within individuals can have implications for plant reproductive success, hence may be under pollinator-mediated phenotypic selection. Most studies on pollinator-mediated selection only evaluate female reproductive success, although floral traits can be under stronger or opposing selection via male fitness. Here we evaluated selection on intra-individual variation and integration of floral traits via its effects on male reproductive success (pollen removal) on a hummingbird-pollinated species. We sampled flowers of Justicia sebastianopolitanae that were exposed to pollinators for 24 h and counted the number of pollen grains that remained in the anthers. We measured corolla length, corolla tube length, anther, and stigma height, as well as herkogamy, display size, and estimated the coefficient of variation (CV) of traits for each individual. We found that the greatest variation in floral traits occurs within individuals. Although intra-individual variation in anther height positively affected pollen removal, we did not detect significant selection, implying that intra-individual variation is not a target for pollinator-mediated selection through male fitness in this plant population. We also found selection on the mean of anther height, indicating the importance of the spatial separation between male and female structures. The variation in anther height may increase the area of pollen deposition on the pollinator's body. Therefore, intra-individual variation could increase the chance of an individual's pollen reaching more stigmas with different heights. We highlight that intra-individual variation should be more widely studied in the context of pollinator-mediated selection and its importance for the reproductive success of individuals in a population.

Do distylous syntopic plant species partition their floral morphological traits?

AbstractMorphological niche partitioning between related syntopic plants that are distylous (with short- and long-styled morphs) is complex. Owing to differences in the heights of stigmas and anthers, each floral morph must place pollen onto two distinct parts of the body of the pollinator. This led us to hypothesize that such partitioning should be more accurate among distylous syntopic species in comparison to combinations with other related plants that do not co-occur. We tested these assumptions using a set of Palicourea (Rubiaceae) species as a model system. We compared the distribution, flowering phenology, floral measurements and reciprocity of sexual organ heights of two syntopic species (Palicourea rigida and Palicourea coriacea) and one non-syntopic congener (Palicourea marcgravii). The three species overlapped in their distributions and flowering periods. The position of sexual organs was, in most cases, partitioned between syntopic populations, with low overlap in anther and stigma heights. However, we found a higher overlap involving the non-syntopic species, especially between Palicourea rigida and Palicourea marcgravii. Additionally, reciprocity of sexual organs was more accurate in intraspecific inter-morph combinations (i.e. legitimate organ correspondence) in comparison to intraspecific intra-morph, interspecific syntopic and interspecific non-syntopic combinations. The partitioning of morphological traits between syntopic species might facilitate the differential placement of pollen on the body of the pollinator and reduce the chances of interspecific interference.

Evolution of Autonomous Selfing in Marginal Habitats: Spatiotemporal Variation in the Floral Traits of the Distylous Primula wannanensis.

Outcrossing plant species are more likely to exhibit autonomous selfing in marginal habitats to ensure reproduction under conditions of limited pollinator and/or mate availability. Distyly is a classical paradigm that promotes outcrossing; however, little is known about the variation in floral traits associated with distylous syndrome in marginal populations. In this study, we compared the variation in floral traits including stigma and anther height, corolla tube length, herkogamy, and corolla diameter between the central and peripheral populations of the distylous Primula wannanensis, and assessed the variation of floral traits at early and late florescence stages for each population. To evaluate the potential consequences of the variation in floral traits on the mating system, we investigated seed set in each population under both open-pollinated and pollinator-excluded conditions. The flower size of both short- and long-styled morphs was significantly reduced in late-opening flowers compared with early opening flowers in both central and peripheral populations. Sex-organ reciprocity was perfect in early opening flowers; however, it was largely weakened in the late-opening flowers of peripheral populations compared with central populations. Of these flowers, disproportionate change in stigma height (elongated in S-morph and shortened in L-morph) was the main cause of reduced herkogamy, and seed set was fairly high under pollinator-excluded condition. Our results provide empirical support for the hypothesis on the evolution of delayed autonomous selfing in marginal populations of distylous species. Unsatisfactory pollinator service is likely to have promoted reproductive assurance of distylous plants with largely reduced herkogamy mimicking “homostyles.”

DISTYLY IN OREOCARYA CRASSIPES (BORAGINACEAE), AN ENDANGERED PLANT SPECIES

Oreocarya crassipes, an endangered angiosperm native to the Trans-Pecos region in southern Brewster County, Texas, exhibits distyly, a breeding system that includes two floral morphs with reciprocal positioning of the anthers and stigmas. The long-style (LS) morph has stigmas above the anthers, and the short-style (SS) morph produces anthers above the stigmas. In the present study, multiple aspects of distyly were examined across four populations of O. crassipes including morph ratios, variation in floral morphology, and patterns of macroscopic and microscopic floral development of the morphs. Morph ratios vary among populations, but for all of the samples pooled the ratio was 1 LS:1 SS. Distyly was observed to be well established in the species, with stigma height, anther height, and stigma-anther separation significantly different between the two morphs. Floral developmental patterns are similar to those in related species, suggesting a conserved and similarly co-opted developmental pathway for the origin of distyly in the genus and relatives.

The role of distyly in pollen flow of the hummingbird-pollinated Palicourea rigida (Rubiaceae)

Distylous species possess two floral morphs: S-morph with short styles and long stamens, and L-morph with long styles and short stamens. The reciprocal positioning of anthers and stigmas is hypothesized to promote legitimate (between-morph) pollination. Deviations from reciprocity can negatively affect legitimate pollen deposition. The functioning of reciprocal herkogamy occurs if pollinators collect pollen of the L- and S-morph on different parts of the body, and then contact the stigmas of the opposite morph. However, few studies provide experimental evidence that the pollen deposition from the two morphs is stratified on the pollinator's body, especially for hummingbirds. We studied three populations of Palicourea rigida Kunth, an abundant shrub of the Neotropical savanna, to test the function of distyly as a mechanism to promote the differential placement of pollen on different parts of the pollinator's body and facilitate legitimate pollination. For this, we quantified high and low organs reciprocity, pollen dimorphism and pollen flow and developed a method for simulating floral visits by hummingbirds (main pollinators) to test whether pollen deposition occurs in a stratified manner on the bill. We found greater reciprocity in low organs, which explains the greater legitimate pollen deposition on S than L stigmas in two populations. In the other population, there was no difference in legitimate pollen deposition between morphs. Our findings corroborate the evolutionary models which have proposed that distyly promotes pollen deposition on specific parts of the pollinator's body. Pollen from S anthers was more deposited at the base of the bill, while pollen from L anthers appeared on the middle section of the bill. This stratified pollen deposition on the hummingbird's bill corresponded to the anther height of the pollen-donor morph and stigma height of the opposite morph, facilitating the reception of legitimate pollen, thus demonstrating the ecological functioning of distyly.

Floral biology and potential hybridization of three sympatric epiphytic bromeliads in Veracruz, Mexico

AbstractIn the Bromeliaceae, hybrids have been engineered for horticultural purposes; in addition, hybrids have been observed in natural habitats. We investigated the hybridization potential of three sympatric species of Tillandsia inhabiting secondary forests and shaded coffee plantations in the central mountains of Veracruz, Mexico. The studied species (T. juncea, T. polystachia and T. variabilis) show overlap in flowering phenology and are believed to share pollinators. We compared the floral morphology of the species, performed controlled intra‐ and interspecific pollinations, and recorded pollen tube growth, fruit and seed set, as well as seed germination. Flower size differed among the species, but stamen and stigma heights were similar between pairs of species, which would facilitate interspecific pollen exchange. Pollen tubes reached the ovary in interspecific crosses. The three species showed interspecific cross‐compatibility, as all crosses resulted in development of mature fruit and viable seeds. Tillandsia juncea achieved the highest fruit set, whereas T. variabilis showed the highest seed set. Seed set as a result of agamospermy, autogamy, geitonogamy and interspecific cross‐pollination did not differ among the species. The findings suggest that pre‐ and post‐pollination barriers are weak among the three species of Tillandsia, which thus could potentially hybridize in natural sympatric populations.

How to build distylous flowers: comparative floral development and evolution of distylous species across the angiosperms.

Distyly, a plant breeding system characterized by two floral morphs that have reciprocal positioning of anthers and stigmas, is known from at least 27 angiosperm families, making it an excellent example of convergent evolution. The various manners in which patterns of floral development produce the distinct anther and stigma heights in each morph remain largely unexplored from developmental and evolutionary perspectives. In 15 species representing at least 12 origins of distyly, heights and lengths of floral organs in each morph throughout development were examined using light microscopy. Patterns of floral organ development were determined and compared among species. Family-level phylogenies of distylous species and relatives were reconstructed, and patterns of ancestral herkogamy were resolved. Differences in floral development between morphs resulted in 12 patterns leading to the anther and stigma positions characterizing distyly. Distylous species evolved from ancestors with different types of herkogamy, with approach herkogamy and lack of herkogamy resolved most frequently. Seven of the 12 patterns of floral development are known from only one species, with three other patterns described among pairs of close relatives. The most common pattern of floral development, described from at least seven genera, involves for anther heights, distinct intermorph growth rates and for stigma heights, growth rates that differ between morphs only during later development. This pattern is common among subclass Lamiidae, suggesting canalized development within the taxon. Among distylous species, the same type of ancestral herkogamy can give rise to different patterns of floral development.

Mating pattern of a distylous primrose in a natural population: unilateral outcrossing and asymmetric selfing between sexual morphs

Heterostyly is a genetic polymorphism of anther and stigma heights, which are reciprocally placed among morphs. The maintenance of heterostyly has often been ascribed to disassortative mating, but alternative explanations are also possible, which can be examined by analyzing mating patterns. However, parental analysis with genetic markers has only been applied to a limited number of taxa, despite the phylogenetic diversity of heterostylous species. Here, we examined the mating patterns of a distylous primrose, Primula kisoana (Primulaceae), in its natural habitat, using 11 microsatellite markers. We also examined other fitness components. We found no differences in seed production, vegetative growth, or survival between morphs. However, the siring success of thrum fathers was much higher than that of pin fathers; outcrossing occurred unilaterally between thrum fathers and pin mothers, and selfing was more frequent in thrum plants than in pin plants. These findings are consistent with the explanation that distyly in this species is maintained either by overdominance due to previously reported recessive lethal effects of the thrum allele or by effectively dioecious mating if inbreeding depression is strong. We built a mathematical model of the overdominance hypothesis to confirm that it is logically sound. These results warrant further investigations into the possible roles of overdominance and dioecy in the maintenance of heterostyly.

Trait patterns across space and time suggest an interplay of facilitation and competition acting on Neotropical hummingbird‐pollinated plant communities

Pollinators may influence plant community assembly through biotic filtering and/or plant–plant competition and facilitation. The relative importance of each process, however, vary according to the scale and how strongly plants share their pollinators, and possibly in relation to the pollinator groups considered. We here investigated the assembly of three Atlantic forest hummingbird‐pollinated plant communities across space (among all species in the communities) and time, i.e. yearly flowering phenology (between pairs of co‐flowering species), based on the pairwise distances of multiple floral traits (corolla length, anther and stigma height, colour and nectar). Because tropical hummingbird‐pollinated plants are often subdivided in two pollination niches (hermits versus non‐hermits), we also analyzed these groups separately. We found that trait structure across space was clustered for some floral traits, suggesting biotic filtering and facilitation. All floral traits had weak phylogenetic signal, indicating that closely related species were not more similar than distantly related species. Moreover, floral traits were randomly structured along the phenology when analyzing all plants together. On the other hand, we found similar corolla length but divergent anther height in co‐flowering pairs within the same pollination niche. Thus, plants may benefit from flowering together and avoid competition through fine adjustments in reproductive traits. The results also suggest that clear signals of competition and facilitation among plants are only apparent when species strongly share their pollinators and depending on the traits that are considered. Our study illustrates a complex interplay of biotic filtering, facilitation and competition as processes structuring guilds of plants sharing the same functional group of pollinators.

Is sexual organ reciprocity related to legitimate pollen deposition in distylous Pulmonaria (Boraginaceae)?

Heterostyly, i.e. the reciprocal positioning of anthers and stigmas, is a floral polymorphism that is thought to promote disassortative (i.e. between‐morph) pollination and to maintain genetic diversity within populations. Recent research, however, has shown several cases of heterostylous plant species in which the reciprocal positioning of the sexual organs varies, which may affect the likelihood of ‘legitimate’ pollination between compatible morphs, and hence morph fitness and ultimately the stability of this floral polymorphism. In this study, we investigated floral morphology and stigmatic pollen deposition patterns in nine Pulmonaria species (Boraginaceae) across Europe to test the hypothesis that sexual organ reciprocity is related to legitimate pollen deposition. We used a recently developed adaptive accuracy concept to assess the level of reciprocity and to relate inaccuracies in positioning of sexual organs to legitimate pollen deposition measured on stigmas in the field. The nine investigated Pulmonaria species showed substantial deviations from perfect reciprocity, with total inaccuracies varying between 2.9 and 20.3% relative to the squared mean of all anther and stigma heights in the population. In almost all cases, most of the inaccuracy was generated by the high‐level organs. Total pollen deposition was always higher on stigmas of long‐styled individuals, but stigmas of short‐styled individuals received significantly more legitimate pollen than stigmas of long‐styled individuals (71.23% and 38.75% respectively). We also found a weak but significant relationship between measures of inaccuracy and the level of disassortative pollination. Under these conditions of pollen flow, the distylous mating system is predicted to persist in only eleven (27%) of all sampled populations. Overall, these results indicate that deviations from perfect reciprocal herkogamy are common in Pulmonaria and have an impact on legitimate pollen deposition.

Gender specialisation and stigma height dimorphism in Mediterranean Lithodora fruticosa (Boraginaceae).

Dimorphism in style height has evolved repeatedly in flowering plants, with some individuals having short and others long styles; in the case of distylous species, stigma position varies reciprocally with that of the anthers. Distyly can be associated with divergence in the functional gender between long‐ and short‐styled individuals, but gender divergence has rarely been investigated in species with a simple stigma height polymorphism in the absence of reciprocal dimorphism in anther position.To evaluate the relation between stigma height polymorphism and gender, I measured the dimensions of floral morphology and seed production for the two morphs of a large population of the Iberian species Lithodora fruticosa (Boraginaceae).Results confirm the existence of a stigma height polymorphism in L. fruticosa, with long‐ and short‐styled individuals at a 1:1 ratio in the studied population. Long‐styled individuals produced substantially more seeds than did short‐styled individuals, pointing to strong divergence in functional gender between the two morphs.The results of this study are puzzling in light of recent work that suggests that L. fruticosa has a multi‐allelic self‐incompatibility system. I discuss the significance of gender divergence in L. fruticosa and evaluate hypotheses that might explain it.

Dimorphic Nature in Stigma-Anther Separation of Prunus nipponica (Rosaceae)

Stigma height, anther height and stigma-anther separation were studied to examine their dimorphic nature in two populations of Prunus nipponica occuring in sub-alpine zone of Mts. Norikura and Tsukush

Genetic and environmental integration of the hawkmoth pollination syndrome in Ruellia humilis (Acanthaceae).

The serial homology of floral structures has made it difficult to assess the relative contributions of selection and constraint to floral integration. The interpretation of floral integration may also be clouded by the tacit, but largely untested, assumption that genetic and environmental perturbations affect trait correlations in similar ways. In this study, estimates of both the genetic and environmental correlations between components of the hawkmoth pollination syndrome are presented for chasmogamous flowers of Ruellia humilis , including two levels of control for serial homology. A greenhouse population for quantitative genetic analysis was generated by a partial diallel cross between field-collected plants. An average of 634 chasmogamous flowers were measured for each of eight floral traits that contribute to the hawkmoth syndrome. Genetic correlations (across parents) and environmental correlations (across replicate flowers) were estimated by restricted maximum likelihood. Stigma height, anther height and floral tube length were very tightly integrated in their responses to both genetic and environmental perturbations. The inclusion of floral disc width as a control for serial homology suggests this integration is an adaptive response to correlational selection imposed by pollinators. In contrast, integration of non-homologous traits was low. Furthermore, when comparisons between the dimensions of serially homologous structures were excluded, the genetic and environmental correlation matrices showed little congruence. The results suggest that hawkmoths have imposed strong correlational selection on floral traits involved in the deposition and removal of pollen, and that this is a consequence of stabilizing selection on the relative positions of stigmas and anthers in the face of substantial flower size variation. Low integration of other floral traits, and conflicting patterns of genetic and environmental correlations among these traits, suggest weak or no correlational selection within the range of variability expressed within a population.

Genetic architecture and evolution of the S locus supergene in Primula vulgaris.

Darwin's studies on heterostyly in Primula described two floral morphs, pin and thrum, with reciprocal anther and stigma heights that promote insect-mediated cross-pollination. This key innovation evolved independently in several angiosperm families. Subsequent studies on heterostyly in Primula contributed to the foundation of modern genetic theory and the neo-Darwinian synthesis. The established genetic model for Primula heterostyly involves a diallelic S locus comprising several genes, with rare recombination events that result in self-fertile homostyle flowers with anthers and stigma at the same height. Here we reveal the S locus supergene as a tightly linked cluster of thrum-specific genes that are absent in pins. We show that thrums are hemizygous not heterozygous for the S locus, which suggests that homostyles do not arise by recombination between S locus haplotypes as previously proposed. Duplication of a floral homeotic gene 51.7 million years (Myr) ago, followed by its neofunctionalization, created the current S locus assemblage which led to floral heteromorphy in Primula. Our findings provide new insights into the structure, function and evolution of this archetypal supergene.

Floral morphs and seed production from hand-pollination in a population of Oxalis corymbosa in Taiwan

Oxalis corymbosa, a tristylous species, lacks seed-set in Taiwan. In a previous survey, six floral types (3 floral morphs in combination with two types of anthers) of 23 populations in Taiwan were assigned based on qualitative visual observation. In this study, we conducted experiments on one of the populations to pursue following objectives: to analyze the floral types of the population based on quantitative measurement and to test the hypothesis that the lack of seed-set is partially attributed to pollination limitation. The heights of anthers and stigmata were measured and analyzed. The number of viable pollen grains per anther was estimated. Pollen germination and seed-production after hand-pollination treatments were examined. Variations in anther and stigma heights were found in each type of previously assigned flowers. Unequal heights of reciprocal sexual organs between floral types were also found. Each level of anthers of MS-Y (mid-styled bearing yellow anthers) and SHS-Y (semi-homostylous bearing yellow anthers) flowers contained about 60 and 25 viable pollen grains, respectively; while anthers of SHS-W (semi-homostylous bearing white anthers) flowers had no pollen. Among hand-pollination treatments of inter-morph, cross-intra-morph and self-intra-morph crossings, only in one inter-morph crossing, i.e. SHS-Y (pollen receiver)×l/MS-Y [pollen donor, pollen from lower (l)-level anthers of MS-Y], pollen tubes were found entering micropyles of the ovules, and seeds were built. Thus, this species can produce seeds by hand-pollination. The result supports that limitation of pollen transfer at least partially contributes to the absence of seed-production in field populations of O. corymbosa in Taiwan.

Pollination ecology of alpine herb Meconopsis integrifolia at different altitudes

Aims We studied the breeding system and pollination ecology of Meconopsis integrifolia (Papaveraceae), which is an alpine herb, for two consecutive years. Methods Five plots (plot 1, 4 452 m a.s.l; plot 2, 4 215 m a.s.l; plot 3, 4 081 m a.s.l; plot 4, 3 841 m a.s.l; plot 5, 3681 m a.s.l) were established along an altitudinal gradient in the Balang Mountain. Flower longevity, stigma height and the highest stamen were measured and recorded. The stigma receptivity and pollen viability were tested by the Benzidine-H2O2 method and the TTC method, respectively. The breeding system was tested by experimental approaches, and flower visitors were observed over the life span of the flower. The temperatures of the flower and environment were also recorded. Important findings Flower longevity was greater in plots 1 and 2 than in plots 3, 4 and 5. The stigmas were higher than the anthers at the beginning of anthesis, and the distance between stigmas and the anthers then gradually decreased with the progress of flowing. The stigmas and anthers came into contact when the corolla wilted in 65% of the flowers sampled, indicating an incomplete herkogamy. The stigmas became receptive before the dehiscence of anthers (protogyny). Under natural conditions, stigma receptivity lasted for 8 d and pollen viability lasted for 2 d. Hand-pollination experiments indicated that M. integrifolia was self-compatible and did not exhibit 2 植物生态学报 Chinese Journal of Plant Ecology 2015, 39 (1): 1–13 www.plant-ecology.com apomixis. Seed set was significantly increased after a supplemental hand-pollination, suggesting the pollen-limitation of reproduction. The pollinators in plots 1 and 2 were flies, and in plots 3, 4 and 5 flies and Thripidae spp. We observed that flies moved and transferred pollen between plants, and that both flies and Thripidae spp. moved within flowers, the latter resulted in “facilitated selfing”. About 65% of the plants sampled set seed by autonomous self-pollination. There was a significant difference in the visiting frequency of flies between plots, with plot 1 being the lowest and plot 2 the highest. Pollen limitations were evident across all plots due to lack of sufficient outcrossing pollinators. Two different selfing mechanisms, unexplored here, may provide a partial compensation for the natural reproduction of this alpine species in the arid, alpine habitats. M. integrifolia could attract pollinators by providing a warm shelter.

Disruption of the distylous syndrome in Primula veris.

Distyly is a floral polymorphism characterized by the presence of two discrete morphs with reciprocal positioning of anthers and stigmas in flowers on different plants within the same population. Although reciprocal herkogamy and associated floral traits are generally thought to be discrete and strict polymorphisms, little is known about variation in floral traits related to the distylous syndrome within and among populations of a single species. In this study, variation in floral morphology and reciprocal positioning of the sexual organs in the distylous Primula veris (cowslip) is quantified. Data were collected in ten populations occurring in two contrasting habitat types (grasslands and forests), and for each population the average level of reciprocity was assessed, the strength of the self-incompatibility system was determined, and seed production under natural conditions was quantified. In grassland populations, flowers showed clear distyly with low and symmetric reciprocity indices at both the lower and upper level. In forests, P. veris produced larger flowers that showed strong deviations in stigma-anther separation, especially in the L-morph. This deviation was mainly driven by variation in stigma height, resulting in high and asymmetric reciprocity indices and the occurrence of several short-styled homostylous plants. Self-incompatibility was, however, strict in both habitats, and morph ratios did not differ significantly from isoplethy. The observed shift in reciprocity in forest populations was associated with a significant reduction in seed production in the L-morph. The results indicate that populations of P. veris show habitat-specific variation in flower morphology. Deviations from perfect reciprocal positioning of stigmas and anthers also translate into reduced seed production, suggesting that small changes in sexual organ reciprocity can have far-reaching ecological and evolutionary implications.