Reproductive success of non-rewarding Cypripedium japonicum benefits from low spatial dispersion pattern and asynchronous flowering

What are the drivers of female success in food-deceptive orchids?

A large suite of floral signals, and environmental and biotic characteristics influence the behavior of pollinators, affecting the female success of food-deceptive orchids. In this study, we examined the many factors shaping the reproductive output of three orchid taxa: Dactylorhiza majalis, D. incarnata var. incarnata, and D. fuchsii. We applied a statistical model to correlate female success (number of fruit sets) with individual characteristics (plant and inflorescence height, number of flowers, and spur length), number of pollinaria removed, flowering time, and density of floral units of co-flowering rewarding plants. Our findings suggested that the broad spectrum of variations in Dactylorhiza's morphological traits, floral display, and flowering phenology within different environmental contexts has a significant impact on their reproductive success. The number of fruits increased with an increase in the number of pollinaria removed in the studied Dactylorhiza taxa. In contrast, a higher number of flowers per inflorescence and higher inflorescences in relation to individual height always decreased fruit set. We observed that low number of co-flowering rewarding plants in populations could affect the Dactylorhiza reproductive output as magnets and competitor plants. The synchronization of flowering, or lack thereof, between Dactylorhiza and rewarding plants can limit reproductive success. This demonstrates that the food deception strategy is multidirectional, and reproductive output can vary considerably both spatially and temporally within the context of this strategy.

Cypripedium lichiangense (Orchidaceae) mimics a humus-rich oviposition site to attract its female pollinator, Ferdinandea cuprea (Syrphidae)

Most species in the genus Cypripedium (Cypripedioideae) produce trap flowers, making it a model lineage to study deceptive pollination. Floral attractants in most species studied appear to target bee species of different sizes. However, more recent publications report fly pollination in some subalpine species, suggesting novel suites of adaptive floral traits. Cypripedium lichiangense (section Trigonopedia) is an endangered subalpine species endemic to the Hengduan Mountains, China. We observed and analysed its floral traits, pollinators and breeding systems over 2 years in situ and in the lab. Cypripedium lichiangense was visited by females of Ferdinandea cuprea (Syrphidae). The pollinia were carried dorsally on the fly thoraces. The eggs of this fly were frequently found in the saccate labellum and on other floral organs, suggesting brood-site mimesis. The orchid is self-compatible, but cross-pollination produces more viable embryos. We propose a new mode of floral mimesis, humus-rich oviposition site mimicry, for C. lichiangense. Compared with the mimesis of aphid colonies attracting syrphid pollinators (subfamily Syrphinae), whose larvae are entomophagic, as reported in some Paphiopedilum species (Cypripedioideae), pollination by deceit in C. lichiangense represents a distinct and separate mode of exploitation of another saprophagic (or phytophagic) larvae syrphid lineage in the subfamily Eristalinae and appears to indicate diversity of pollination strategies in Section Trigonopedia of Cypripedium. However, this new brood-site mimesis seems to be less attractive to pollinators. As a possible adaptation to the weak attracted pollination strategy, this plant species has a long flowering period and extended lifespan of individual flowers to ensure reproductive success.

Environmental conservation value of an endangered species: the case of Cypripedium Japonicum

The South Korean government is seeking information on the environmental conservation value (ECV) of Cypripedium japonicum, a plant on the first-level priority endangered species list of the Korea Ministry of Environment, as well as on the Red List of the International Union for Conservation of Nature. This research paper aims to assess the ECV by employing contingent valuation (CV) to elicit people's willingness to pay (WTP) for its conservation. To achieve this aim, in May 2020, a CV survey of 1,000 interviewees in South Korea was carried out employing a closed-ended question. The average household WTP is estimated to be KRW 3,770 (USD 3.07) per annum and secures statistical significance. From a national point of view, using information on the national population, this value comes to KRW 76.72 billion (USD 62.42 million) per year. Although the cost of conserving the species has not yet been accurately estimated, the ECV seems to be larger than the cost of conservation. Thus, it is socially desirable to conserve Cypripedium japonicum, and the conservation should be carried out in a stable and continuous manner.

Modelling the Effects of Climate Change on the Distribution of Endangered Cypripedium japonicum in China

Cypripedium japonicum is an endangered terrestrial orchid species with high ornamental and medicinal value. As global warming continues to intensify, the survival of C. japonicum will be further challenged. Understanding the impact of climate change on its potential distribution is of great significance to conserve this species. In this study, we established an ensemble species distribution model based on occurrence records of C. japonicum and 13 environmental variables to predict its potential distribution under current and future climatic conditions. The results show that the true skill statistic (TSS), Cohen’s kappa statistic (Kappa), and the area under the receiver operating characteristic curve (AUC) values of the ensemble model were 0.968, 0.906, and 0.995, respectively, providing more robust predictions. The key environmental variables affecting the distribution of C. japonicum were the precipitation in the warmest quarter (Bio18) and the mean temperature in the driest quarter (Bio9). Under future climatic conditions, the total suitable habitat of C. japonicum will increase slightly and tend to migrate northwestward, but the highly suitable areas will be severely lost. By 2070, the loss of its highly suitable habitat area will reach 57.69–72.24% under representative concentration pathway (RCP) 4.5 and 8.5 respectively, and the highly suitable habitats in Zhejiang and Anhui will almost disappear. It is noteworthy that the highly suitable habitat of C. japonicum has never crossed the Qinba mountainous area during the migration process of the suitable habitat to the northwest. Meanwhile, as the best-preserved area of highly suitable habitat for C. japonicum in the future, the Qinba mountainous area is of great significance to protect the wild germplasm resources of C. japonicum. In addition, we found that most of the changes predicted for 2070 will already be seen in 2050; the problem of climate change may be more urgent than it is believed.

Gametophyte and embryonic ontogeny: understanding the reproductive calendar of Cypripedium japonicum Thunb. (Cypripedoideae, Orchidaceae), a lady's slipper orchid endemic to East Asia

BACKGROUND

The genus Cypripedium L. is one of the five genera of the subfamily Cypripedioideae, members of which are commonly known as lady's slipper orchids. Cypripedium japonicum is a perennial herb native to East Asia, specifically China, Japan, and Korea. Due to its limited distribution, the species is included in the Endangered category of the IUCN Red List.

RESULTS

We investigated gametophyte development, including complete embryogenesis, in C. japonicum. The complete reproductive cycle is presented based on our observations. Anther development begins under the soil, and meiosis of pollen mother cells begins 3 weeks before anthesis, possibly during early April. The megaspore mother cells develop just after pollination in early May and mature in mid-late June. The pattern of embryo sac formation is bisporic, and there are six nuclei: three forming the egg apparatus, two polar nuclei, and an antipodal cell in the mature embryo sac. Triple fertilization results in the endosperm nucleus, which degenerates when the proembryo reaches the eight-to-sixteen-cell stage.

CONCLUSION

Our overall comparisons of the features of gametophyte and embryo development in C. japonicum suggest that previous reports on the embryology of Cypripedium are not sufficient for characterization of the entire genus. Based on the available information, a reproductive calendar showing the key reproductive events leading to embryo formation has been prepared.

Pollinators and visitors of the generalized food-deceptive orchid Dactylorhiza majalis in North-Eastern Poland

Pollinator foraging behavior plays a key role in breeding and therefore affects the evolution of the orchid reproductive strategy. Food-deceptive orchids usually implement a generalized plant pollination strategy and a relatively diverse group of pollinators visit them. Dactylorhiza majalis is a food-deceptive, early-flowering orchid that relies on insect-mediated pollination. This study’s objectives were to identify D. majalis’ pollinators and flower visitors and their foraging behaviors on D. majalis inflorescences. We also assessed the bending movement time to determine the relationship between bending time and the duration of pollinators’ visits. To assess pollination efficiency, we measured the spur length of D. majalis flowers, which is expected to affect the mechanical fit to pollinators/“potential” pollinators. The arthropod fauna were investigated to examine the availability of “potential” pollinators in populations. We identified Apis mellifera as this orchid’s main pollinator and confirmed that few of the flower visitors belonged to Diptera (12 individuals, 9 taxa), Hymenoptera (3 individuals, 3 taxa), or Coleoptera (2 individuals, 2 taxa) in our dataset, which was collected over a 2-year period and includes 360 h of video. The arthropods were collected by a sweep net in D. majalis populations and there were fewer Hymenoptera (2.9–23.2%) and Coleoptera (4.4–23.8%) visitors but more Diptera (23.3–58.6%) visitors. We found that A. mellifera foraged in different ways on D. majalis inflorescences, thereby resulting in cross-pollination and/or geitonogamy; however, the bending time data supported the hypothesis about promoting cross-pollination while decreasing self-pollination, but these data do not exclude the possibility of geitonogamy.

Reproductive consequences of variation in flowering phenology in the dry forest tree Enterolobium cyclocarpum in Guanacaste, Costa Rica

PREMISE OF THE STUDY

Flowering initiation, duration and magnitude, and degree of flowering synchrony within a population can affect the reproductive fitness of individuals. We examined the flowering phenology within a population of the tropical dry forest Guanacaste tree (Enterolobium cyclocarpum) to gauge the impact of phenological variation among trees on fruit production and progeny vigor.

METHODS

We monitored the flowering phenology of 93 trees weekly during 2005, 2006, and 2007, using a scale based on the percentage of the crown with open flowers. We also monitored fruit production for each tree in 2005, 2006, 2007, and 2008. Finally, we evaluated the relationship between phenological variation and progeny performance.

KEY RESULTS

Ten measures of flowering phenology and synchrony among flowering trees, based on the number of weeks when anthesis of the crown exceeded 50%, were used to develop four phenological profiles. These profiles were correlated with significant differences in fruit production and progeny vigor. Trees with flowers in >50% of their crown for at least 2 weeks produced more fruits and more vigorous progeny than trees with other profiles. Trees also tended to produce the same phenological profile among years than predicted by chance.

CONCLUSIONS

Guanacaste trees vary significantly in the initiation of anthesis, duration and magnitude of flowering, and degree of synchrony among trees. Trees also tend to maintain the same flowering profile among years. Finally, the flowering behavior of E. cyclocarpum leads to significant differences in fruit and seed production, germination, and early progeny growth.

Genetic diversity in the endangered terrestrial orchid Cypripedium japonicum in East Asia: Insights into population history and implications for conservation

Little is known about levels and patterns of genetic diversity for the entire range of endangered orchids native to China, Korea, and Japan. In this study, we focus on Cypripedium japonicum and suggest three hypotheses: 1) that genetic drift has been a primary evolutionary force; 2) that populations in central and western China harbor higher levels of genetic variation relative to those from eastern China; and 3) that C. japonicum in China maintains the highest genetic variation among the three countries. Using ISSR and SCoT markers, we investigated genetic diversity in 17 populations to test the three hypotheses. As anticipated, we found low levels of genetic diversity at the species level with substantially high degree of genetic divergence, which can be mainly attributed to random genetic drift. Chinese populations harbor the highest within-population genetic variation, which tends to increase from east to west. We also found a close relationship between Korean populations and central/western Chinese populations. Historical rarity coupled with limited gene flow seems to be important factors for shaping genetic diversity and structure of C. japonicum. Our results indicate that the mountain areas in central and western China were likely refugia at the Last Glacial Maximum.

Spatio-temporal arrangement of Chamaerops humilis inflorescences and occupancy patterns by its nursery pollinator, Derelomus chamaeropsis

BACKGROUND AND AIMS

Nursery pollination is a highly specialized interaction in which pollinators breed inside plant reproductive structures. Pollinator occupancy of host plants often depends on plant location, flowering synchrony and sex. The nursery pollination system between the dioecious dwarf palm Chamaerops humilis (Arecaceae) and the host-specific palm flower weevil Derelomus chamaeropsis was investigated. For the first time, sex, flowering synchrony and spatial distribution of plants was related to the occupancy probability and the abundance of D. chamaeropsis larvae, important traits influencing both pollinator and plant fitness.

METHODS

During the flowering season, all inflorescences in anthesis were counted every 12 d and a flowering synchrony index was calculated taking into account all possible correlations with generalized linear mixed models. To analyse the spatial structure of plants, larva occupancy and abundance, different techniques of spatial point pattern analysis were used.

KEY RESULTS

In total, 5986 larvae in 1063 C. humilis inflorescences were recorded over three consecutive seasons. Male inflorescences showed a higher presence and abundance of weevil larvae than females, but interestingly approx. 30 % of the females held larvae. Also, larvae occurred mainly in highly synchronous plants with a low number of inflorescences, perhaps because those plants did not lead to a resource dilution effect. There was no evidence of spatial patterns in larva occupancy or abundance at any spatial scale, suggesting high dispersal ability of adult weevil.

CONCLUSIONS

The results in a nursery-pollinated dioecious palm demonstrate that plant sex, flowering display and flowering synchrony act as additive forces influencing the presence and abundance of the specialized pollinator larvae. Contradicting previous results, clear evidence that female dwarf palms also provide rewarding oviposition sites was found, and thus the plant 'pays' for the pollination services. The findings highlight that plant local aggregation is not always the main determinant of pollinator attraction, whereas flower traits and phenology could be critical in specialized plant-pollinator interactions.

Consequences of asynchronous heading in a perennial bunchgrass (Elymus excelsus)

Reproduction is vital to plant population adaptation. The consequences of asynchronous reproduction in a perennial bunchgrass grass is not well studied. The heading reproductive tillers from early to late forms a continuum due to asynchronous heading and flowering in Elymus excelsus population. In two peak years of production, the three-year-old and four-year-old reproductive tillers of experimental E. excelsus population were marked from the early to late heading stage every four days at five different heading times and these tillers were harvested at the dough stage, respectively. The growth, biomass, seed production and reproductive allocation were measured to analyze the consequences of asynchronous reproduction. Reproductive tiller height, biomass, inflorescence length, inflorescence biomass, floret number, seed number, seed biomass, seed-set percentage, biomass allocation to inflorescence (RA1) and to seed (RA2) significantly decreased with the delay of heading date over the two years. Above ten phenotypic characteristics exponentially increased at a significant or extremely significant level with increasing differences in reproductive period. Reproductive tillers preferentially allocated the biomass to inflorescences, and then the inflorescences preferentially allocated the biomass to seeds throughout reproductive period. Earlier heading tillers had more contribution to E. excelsus population adaptation and development in the two peak years of production.

Hormonal and morphological changes during seed development of Cypripedium japonicum

With the goal of evaluating the factors that may be influencing the reproductive success of an endangered, terrestrial orchid Cypripedium japonicum Thunb., the anatomical and morphological characteristics of seed development were assessed, as were the levels of endogenous hormones to investigate the possible relationship between hormones and seed development. The results showed that morphological characteristics of seeds were changing from milky white and filiform to brown and fusiform. The development of ovule that initiated on the fertile valves only began after pollination, and a mature embryo sac was produced at 40 days after pollination (DAP). Fertilization occurred 50 to 60 DAP, and the newly formed zygote divided into two unequal cells that became the embryo proper and the suspensor. Seeds reached maturity at about 115 DAP, at which point they consisted only of a globular embryo and two layers of seed coat, without endosperm. The suspensor was lost, and only lipid particles and a large number of starch grains distributed in the cytoplasm. The peak of gibberellic acid (GA₃), zeatin riboside (ZR), and indole acetic acid (IAA) occurred in a time sequence, as 20, 30, and 40 DAP. There was a highly significant positive correlation among them (P < 0.01). Abscisic acid (ABA) content increased at 60 DAP and reached the maximum at 115 DAP. ABA contents were significantly negatively correlated with the three hormones above (P < 0.05). It indicated that the lack of endosperm and suspensor tissues, delayed differentiation of embryos, and high levels of ABA may lead to the difficulty of germination.

Fluctuating selection across years and phenotypic variation in food-deceptive orchids

Nectarless flowers that deceive pollinators offer an opportunity to study asymmetric plant-insect interactions. Orchids are a widely used model for studying these interactions because they encompass several thousand species adopting deceptive pollination systems. High levels of intra-specific phenotypic variation have been reported in deceptive orchids, suggesting a reduced consistency of pollinator-mediated selection on their floral traits. Nevertheless, several studies report on widespread directional selection mediated by pollinators even in these deceptive orchids. In this study we test the hypothesis that the observed selection can fluctuate across years in strength and direction thus likely contributing to the phenotypic variability of this orchid group. We performed a three-year study estimating selection differentials and selection gradients for nine phenotypic traits involved in insect attraction in two Mediterranean orchid species, namely Orchis mascula and O. pauciflora, both relying on a well-described food-deceptive pollination strategy. We found weak directional selection and marginally significant selection gradients in the two investigated species with significant intra-specific differences in selection differentials across years. Our data do not link this variation with a specific environmental cause, but our results suggest that pollinator-mediated selection in food-deceptive orchids can change in strength and in direction over time. In perennial plants, such as orchids, different selection differentials in the same populations in different flowering seasons can contribute to the maintenance of phenotypic variation often reported in deceptive orchids.

When it pays to cheat: Examining how generalized food deception increases male and female fitness in a terrestrial orchid

Background

Experimental manipulations of floral nectar in food deceptive species can reveal insights into the evolutionary consequences of the deceptive strategy. When coupled to pollen tracking, the effects of the deceptive pollination syndrome on both male and female reproductive success may be quantified. Attraction of pollinators in deceit-pollinated species often relies on producing a conspicuous floral display which may increase visibility to pollinators, but in-turn may increase within plant selfing.

Methodology

To understand the role of deception in Orchidaceae reproduction we studied Cypripedium candidum. All species of the Cypripedium genus employ a generalized food deceptive pollination strategy and have been suggested as a model system for the study of pollinator deception. We conducted a nectar addition experiment that randomly assigned the four plants closest to a transect point to receive one of four histochemical dyes. Two individuals selected for nectar addition in each of altogether 25 blocks received 2μl of 25% sucrose solution in the labellum of each flower, while two others received no artificial nectar. Number of fruits produced, fruit mass and fruit abortion were scored at the end of the four-month experiment.

Results

Nectar addition increased (p<0.0001) self-pollination and pollen discounting by nearly 3x, while plants not receiving nectar had greater (p<0.0001) numbers of non-self pollinia deposited and lower rates of pollen discounting. There was a non-significant (p = 0.0645) trend for deceptive plants to set more fruit, while presence of nectar did not affect pollen export.

Conclusions

This study demonstrates the adaptive advantages of food deception by showing a concurrent reduction in particular male and female functions when a food reward is restored to a deceptive flower. We found generalized food deception to not only decrease inbreeding depression in the system, but concurrently have no effect on pollinator attraction and fruit set when compared with rewarding flowers.

The causes of selection on flowering time through male fitness in a hermaphroditic annual plant

Flowering is a key life-history event whose timing almost certainly affects both male and female fitness, but tests of selection on flowering time through male fitness are few. Such selection may arise from direct effects of flowering time, and indirect effects through covariance between flowering time and the environment experienced during reproduction. To isolate these intrinsically correlated associations, we staggered planting dates of Brassica rapa families with known flowering times, creating populations in which age at flowering (i.e., flowering time genotype) and Julian date of flowering (i.e., flowering time environment) were positively, negatively, or uncorrelated. Genetic paternity analysis revealed that male fitness was not strongly influenced by seasonal environmental changes. Instead, when age and date were uncorrelated, selection through male fitness strongly favored young age at flowering. Strategic sampling offspring for paternity analysis rejected covariance between sire age at flowering and dam quality as the cause of this selection. Results instead suggest a negative association between age at flowering and pollen competitive ability. The manipulation also revealed that, at least in B. rapa, the often-observed correlation between flowering time and flowering duration is environmental, not genetic, in origin.

Conservation genetics of an endangered lady's slipper orchid: Cypripedium japonicum in China

Knowledge about the population genetic variation of the endangered orchid, Cypripedium japonicum, is conducive to the development of conservation strategies. Here, we examined the levels and partitioning of inter-simple sequence repeat (ISSR) diversity (109 loci) in five populations of this orchid to gain insight into its genetic variation and population structure in Eastern and Central China. It harbored considerably lower levels of genetic diversity both at the population (percentage of polymorphic loci (PPL) = 11.19%, Nei’s gene diversity (H) = 0.0416 and Shannon’s information index (I) = 0.0613) and species level (PPL = 38.53%, H = 0.1273 and I = 0.1928) and a significantly higher degree of differentiation among populations (the proportion of the total variance among populations (Φ_pt) = 0.698) than those typical of ISSR-based studies in other orchid species. Furthermore, the Nei’s genetic distances between populations were independent of the corresponding geographical distances. Two main clusters are shown in an arithmetic average (UPGMA) dendrogram, which is in agreement with the results of principal coordinate analysis (PCoA) analysis and the STRUCTURE program. In addition, individuals within a population were more similar to each other than to those in other populations. Based on the genetic data and our field survey, the development of conservation management for this threatened orchid should include habitat protection, artificial gene flow and ex situ measures.

Effects of pollination limitation and seed predation on female reproductive success of a deceptive orchid

For many species of conservation significance, multiple factors limit reproduction. This research examines the contributions of plant height, number of flowers, number of stems, pollen limitation and seed predation to female reproductive success in the deceit-pollinated orchid, Cypripedium candidum. The deceptive pollination strategy employed by many orchids often results in high levels of pollen limitation. While increased floral display size may attract pollinators, C. candidum's multiple, synchronously flowering stems could promote selfing and also increase attack by weevil seed predators. To understand the joint impacts of mutualists and antagonists, we examined pollen limitation, seed predation and the effects of pollen source over two flowering seasons (2009 and 2011) in Ohio. In 2009, 36 pairs of plants size-matched by flower number, receiving either supplemental hand or open pollination, were scored for fruit maturation, mass of seeds and seed predation. Pollen supplementation increased proportion of flowers maturing into fruit, with 87 % fruit set when hand pollinated compared with 46 % for naturally pollinated flowers. Inflorescence height had a strong effect, as taller inflorescences had higher initial fruit set, while shorter stems had higher predation. Seed predation was seen in 73 % of all fruits. A parallel 2011 experiment that included a self-pollination treatment and excluded seed predators found initial and final fruit set were higher in the self and outcross pollination treatments than in the open-pollinated treatment. However, seed mass was higher in both open pollinated and outcross pollination treatments compared with hand self-pollinated. We found greater female reproductive success for taller flowering stems that simultaneously benefited from increased pollination and reduced seed predation. These studies suggest that this species is under strong reinforcing selection to increase allocation to flowering stem height. Our results may help explain the factors limiting seed production in other Cypripedium and further emphasize the importance of management in orchid conservation.

Bumble-bee learning selects for both early and long flowering in food-deceptive plants

Most rewardless orchids engage in generalized food-deception, exhibiting floral traits typical of rewarding species and exploiting the instinctive foraging of pollinators. Generalized food-deceptive (GFD) orchids compete poorly with rewarding species for pollinator services, which may be overcome by flowering early in the growing season when relatively more pollinators are naive and fewer competing plant species are flowering, and/or flowering for extended periods to enhance the chance of pollinator visits. We tested these hypotheses by manipulating flowering time and duration in a natural population of Calypso bulbosa and quantifying pollinator visitation based on pollen removal. Both early and long flowering increased bumble-bee visitation compared with late and brief flowering, respectively. To identify the cause of reduced visitation during late flowering, we tested whether negative experience with C. bulbosa (avoidance learning) and positive experience with a rewarding species, Arctostaphylos uva-ursi, (associative learning) by captive bumble-bees could reduce C. bulbosa's competitiveness. Avoidance learning explained the higher visitation of early- compared with late-flowering C. bulbosa. The resulting pollinator-mediated selection for early flowering may commonly affect GFD orchids, explaining their tendency to flower earlier than rewarding orchids. For dissimilar deceptive and rewarding sympatric species, associative learning may additionally favour early flowering by GFD species.

Reproductive isolation and pollination success of rewarding Galearis diantha and non-rewarding Ponerorchis chusua (Orchidaceae)

BACKGROUND AND AIMS

Increasing evidence challenges the conventional perception that orchids are the most distinct example of floral diversification due to floral or prezygotic isolation. Regarding the relationship between co-flowering plants, rewarding and non-rewarding orchids in particular, few studies have investigated whether non-rewarding plants affect the pollination success of rewarding plants. Here, floral isolation and mutual effects between the rewarding orchid Galearis diantha and the non-rewarding orchid Ponerorchis chusua were investigated.

METHODS

Flowering phenological traits were monitored by noting the opening and wilting dates of the chosen individual plants. The pollinator pool and pollinator behaviour were assessed from field observations. Key morphological traits of the flowers and pollinators were measured directly in the field. Pollinator limitation and interspecific compatibility were evaluated by hand-pollination experiments. Fruit set was surveyed in monospecific and heterospecific plots.

KEY RESULTS

The species had overlapping peak flowering periods. Pollinators of both species displayed a certain degree of constancy in visiting each species, but they also visited other flowers before landing on the focal orchids. A substantial difference in spur size between the species resulted in the deposition of pollen on different regions of the body of the shared pollinator. Hand-pollination experiments revealed that fruit set was strongly pollinator-limited in both species. No significant difference in fruit set was found between monospecific plots and heterospecific plots.

CONCLUSIONS

A combination of mechanical isolation and incomplete ethological isolation eliminates the possibility of pollen transfer between the species. These results do not support either the facilitation or competition hypothesis regarding the effect of nearby rewarding flowers on non-rewarding plants. The absence of a significant effect of non-rewarding P. chusua on rewarding G. diantha can be ascribed to low levels of overlap between the pollinator pools of two species.

Pollinator-mediated selection on floral display, spur length and flowering phenology in the deceptive orchid Dactylorhiza lapponica

• Nonrewarding animal-pollinated plants commonly experience severe pollen limitation, which should result in strong selection on traits affecting the success of pollination. However, the importance of pollinators as selective agents on floral traits in deceptive species has not been quantified experimentally. • Here, we quantified pollinator-mediated selection (Δβ(poll)) on floral morphology and start of flowering in the deceptive orchid Dactylorhiza lapponica by subtracting estimates of selection gradients for plants receiving supplemental hand-pollination from estimates obtained for open-pollinated control plants. • There was directional selection for taller plants with more flowers and longer spurs, but no statistically significant selection on corolla size or flowering start. Pollinator-mediated selection accounted for all observed selection on spur length (Δβ(poll) = 0.32), 76% of the selection on plant height (Δβ(poll) = 0.19) and 42% of the selection on number of flowers (Δβ(poll = 0.30). Sixteen per cent of developing fruits were consumed by insect herbivores, but fruit herbivory had only minor effects on the strength of pollinator-mediated selection. • Our results demonstrate that pollinators mediate selection on floral traits likely to affect both pollinator attraction and pollination efficiency, and are consistent with the hypothesis that deceptive species experience strong selection for increased display and mechanical fit between flower and pollinator.