Flower-pollinator Interactions Research Articles

Secretory Tissues and Volatile Components of Disc Florets in Several Wild Helianthus L. Species

Although flower pollinator interactions are known to be mediated by floral traits, not enough attention has been paid to the research of secretory tissues and volatile components of sunflower disc florets as potentially important parameters in breeding programs. (1) To our knowledge, this is the first integrated study aimed at better understanding the attractiveness of sunflower capitula to insects. In the study, we have made a very detailed comparative analysis of secretory tissues and the characterization of the volatile components (VOCs) of disc florets in 10 wild perennial Helianthus species. (2) For anatomical analyses, cross-sections were obtained from the nectary zone of disc florets using a cryotechnique procedure. Micromorphological observation and morphological and anatomical analysis of disc florets were performed using light and scanning electron microscopy. For VOCs, we applied headspace, GC-FID, and GC/MS analyses. (3) The obtained results indicate that there is a difference between the analyzed traits among studied species. H. eggertii, H. hirsutus, H. mollis, H. resinosus, and H. tuberosus had high disc diameter values, a high cross-section area and disc floret corolla length, as well as the largest cross-section area and thickness of the disc florets nectary. In the analyzed VOCs, 30 different compounds were detected. The highest yield and quantity of α-Pinene was observed in H. mollis. (4) Inflorescence features, such as receptacle diameter, corolla and secretory tissue properties, and floret VOCs production and characterization, provided valuable information that can be used as guidelines in sunflower breeding programs to maximize pollinator attractiveness and increase seed yield.

Developmental and temporal changes in petunia petal transcriptome reveal scent-repressing plant-specific RING-kinase-WD40 protein.

In moth-pollinated petunias, production of floral volatiles initiates when the flower opens and occurs rhythmically during the day, for optimal flower-pollinator interaction. To characterize the developmental transcriptomic response to time of day, we generated RNA-Seq databases for corollas of floral buds and mature flowers in the morning and in the evening. Around 70% of transcripts accumulating in petals demonstrated significant changes in expression levels in response to the flowers' transition from a 4.5-cm bud to a flower 1 day postanthesis (1DPA). Overall, 44% of the petal transcripts were differentially expressed in the morning vs. evening. Morning/evening changes were affected by flower developmental stage, with a 2.5-fold larger transcriptomic response to daytime in 1DPA flowers compared to buds. Analyzed genes known to encode enzymes in volatile organic compound biosynthesis were upregulated in 1DPA flowers vs. buds-in parallel with the activation of scent production. Based on analysis of global changes in the petal transcriptome, PhWD2 was identified as a putative scent-related factor. PhWD2 is a protein that is uniquely present in plants and has a three-domain structure: RING-kinase-WD40. Suppression of PhWD2 (termed UPPER - Unique Plant PhEnylpropanoid Regulator) resulted in a significant increase in the levels of volatiles emitted from and accumulated in internal pools, suggesting that it is a negative regulator of petunia floral scent production.

Flower-Pollinator Interactions in Liana ( Caesalpinia cucullataRoxb.) in a Tropical Rain Forest of Mizoram

Lianas (woody climbers) are relatively underexplored life forms of many forests, which predominantly forms tropical forests and provide food and shelter to a variety of animals. A study on flower-pollinator interactions in Roxb. was conducted in the Caesalpinia cucullatatropical rain forest of Indo-Burma hot spot at Tanhril area of Aizawl district of Mizoram. Floral visitors of were monitored and C. cucullatarecorded during 24 field days, four to six hour per day with a total of about one hundred hours during the flowering season of November–December, 2016. The flowers of were found to be visited by three insect species belonging three families; nine C. cucullata passeriformes birds belonging eight families and one Hoary-bellied Himalayan squirrel (Irrawaddy squirrel) belonging family Scuiridae. Birds and squirrel mainly visited the flowers in morning hours while butterflies and bee exhibited diurnal pattern of foraging. The results revealed s that the bird pollination is supported by butterflies in . The flowers of would be excellent food resource to the dependent C. cucullata C. cucullata animal species during dry cold period in the extreme tropical sloppy mountain forest site when availability of floral resource is very scarce. Therefore, could be a valuable liana species for the conservation of valuable species of insects, birds and squirrels.

Plant provenance affects pollinator network: Implications for ecological restoration

Abstract The selection of plant provenance for ecological restoration is an intensively debated topic. Throughout this debate, arguments mostly focus on plant performance, but little attention is paid to the effects of provenance on other members of the restored ecosystem. On the other hand, in restoration projects that focus specifically on supporting interacting biota, for example, wildflower strips among fields to support pollinators, the provenance choice is often not considered, partly because the effect of provenance on pollinators is unknown. In this pioneering case study, we tested whether pollinators differentiate between experimental plant communities of different provenances. We established experimental plant communities with the same species composition but with plants originating from three different provenances. We then recorded plant phenology and observed pollinators and flower visitors interacting with these experimental communities and related the pollinator visitation to the provenance identity. The provenances of the experimental plant communities had a strong and significant effect on the diversity and abundance of flower–pollinator interactions, with one provenance interacting two times as often as the other two provenances. The effect was driven by the differences in flowering phenology among provenances. Synthesis and applications. Plant provenances substantially differ in their interactions with local pollinators. Therefore, the selection of plant provenance should be considered when planning restoration projects for the support of pollinators.

Evaluation of sampling effort required to assess pollen species richness on pollinators using rarefaction.

PremiseUnderstanding the flower visitation history of individual pollinators is key in the study of pollination networks, but direct tracking is labor intensive and, more important, does not capture information about the previous interactions of an individual. Therefore, a protocol to detect most of the pollen species on the body surfaces of an individual pollinator could elucidate its flower visitation history.Methods and ResultsUnder a microscope, we observed 6.0‐µL droplets from a sample solution (1.0 or 3.0 mL) containing pollen grains collected from individuals of six major pollinator functional groups. To clarify how many droplets need to be observed to detect all pollen species within the solution, we examined up to 10 droplets collected from each individual insect. Sample‐based rarefaction curve analyses of the data showed that we could detect ~90% of the pollen species and the plant–pollinator links in the networks by observing six droplets.ConclusionsThe rarefaction curve analysis for pollen‐on‐pollinator studies is a useful preliminary step for minimizing the time and labor required while maximizing the data on the flower visitation history of each individual pollinator and revealing any hidden flower–pollinator interactions.

Spatial variability in a plant–pollinator community across a continuous habitat: high heterogeneity in the face of apparent uniformity

Large‐scale spatial variability in plant–pollinator communities (e.g. along geographic gradients, across different landscapes) is relatively well understood. However, we know much less about how these communities vary at small scales within a uniform landscape. Plants are sessile and highly sensitive to microhabitat conditions, whereas pollinators are highly mobile and, for the most part, display generalist feeding habits. Therefore, we expect plants to show greater spatial variability than pollinators. We analysed the spatial heterogeneity of a community of flowering plants and their pollinators in 40 plots across a 40‐km2area within an uninterrupted Mediterranean scrubland. We recorded 3577 pollinator visits to 49 plant species. The pollinator community (170 species) was strongly dominated by honey bees (71.8% of the visits recorded). Flower and pollinator communities showed similar beta‐diversity, indicating that spatial variability was similar in the two groups. We used path analysis to establish the direct and indirect effects of flower community distribution and honey bee visitation rate (a measure of the use of floral resources by this species) on the spatial distribution of the pollinator community. Wild pollinator abundance was positively related to flower abundance. Wild pollinator visitation rate was negatively related to flower abundance, suggesting that floral resources were not limiting. Pollinator and flower richness were positively related. Pollinator species composition was weakly related to flower species composition, reflecting the generalist nature of flower–pollinator interactions and the opportunistic nature of pollinator flower choices. Honey bee visitation rate did not affect the distribution of the wild pollinator community. Overall, we show that, in spite of the apparent physiognomic uniformity, both flowers and pollinators display high levels of heterogeneity, resulting in a mosaic of idiosyncratic local communities. Our results provide a measure of the background of intrinsic heterogeneity within a uniform habitat, with potential consequences on low‐scale ecosystem function and microevolutionary patterns.

Ultraviolet patterns of flowers revealed in polymer replica - caused by surface architecture.

Angiosperms and their pollinators are adapted in a close co-evolution. For both the plants and pollinators, the functioning of the visual signaling system is highly relevant for survival. As the frequency range of visual perception in many insects extends into the ultraviolet (UV) region, UV-patterns of plants play an important role in the flower–pollinator interaction. It is well known that many flowers contain UV-absorbing pigments in their petal cells, which are localized in vacuoles. However, the contribution of the petal surface microarchitecture to UV-reflection remains uncertain. The correlation between the surface structure and its reflective properties is also relevant for biomimetic applications, for example, in the field of photovoltaics. Based on previous work, we selected three model species with distinct UV-patterns to explore the possible contribution of the surface architecture to the UV-signaling. Using a replication technique, we transferred the petal surface structure onto a transparent polymer. Upon illumination with UV-light, we observed structural-based patterns in the replicas that were surprisingly comparable to those of the original petals. For the first time, this experiment has shown that the parameters of the surface structure lead to an enhancement in the amount of absorbed UV-radiation. Spectrophotometric measurements revealed up to 50% less reflection in the UV-absorbing regions than in the UV-reflecting areas. A comparative characterization of the micromorphology of the UV-reflecting and UV-absorbing areas showed that, in principle, a hierarchical surface structure results in more absorption. Therefore, the results of our experiments demonstrate the structural-based amplification of UV-reflection and provide a starting point for the design of bioinspired antireflective and respectively strongly absorbing surfaces.

Elena M. Kramer.

Elena M. Kramer.

One for all and all for one: retention of colour-unchanged old flowers increases pollinator attraction in a hermaphroditic plant.

Long-lived flowers increase pollen transfer rates, but these entail high water and carbon maintenance costs. The retention of pollinated and reward-free old flowers enhances pollinator visitation to young receptive flowers by increasing floral display size. This mechanism is associated with acropetal inflorescences or changes in flower colour and openness, but the retention of unchanging solitary flowers remains overlooked. We examined pollination-dependent variation in floral longevity and determined stigmatic receptivity, pollen viability and pollen removal rates among flower ages in Kielmeyera regalis, a Neotropical savanna shrub. We also evaluated the effects of floral display size on pollinator visitation rates. Lastly, we determined whether old flowers are unvisited and exclusively increase pollinator attraction to young flowers through flower removal experiments. Regardless of pollination treatment, flowers lasted fully open with no detectable physical changes for 3days. Over time, stigmas remained receptive but >95% of pollen was removed. Pollinator visitation significantly increased with floral display size and intermediate percentages (15-30%) of newly opened flowers. Accordingly, the retention of reward-free and unvisited old flowers increased young flower-pollinator interaction. Our results reveal the importance of a prolonged floral longevity in increasing pollinator attraction toward newly opened receptive flowers without changes in flower colour and form. We conclude that the retention of pollinated, reward-free and unvisited colour-unchanged old flowers in K. regalis is a strategy that counteracts the water use costs associated with the maintenance of large flowers with increased mate opportunities in a pollen-limited scenario.

The costs and benefits of pollinator dependence: empirically based simulations predict raspberry fruit quality.

Globally, agriculture increasingly depends on pollinators to produce many seed and fruit crops. However, what constitutes optimal pollination service for pollinator-dependent crops remains unanswered. We developed a simulation model to identify the optimal pollination service that maximizes fruit quality in crops. The model depicts the pollination (i.e., autonomous self-fertilization, pollen deposition) and post-pollination (i.e., pollen germination, and time from germination to ovule fertilization) processes leading to fruit and seed set and allows for negative flower-pollinator interactions, specifically pistil damage. We parameterized and validated the model based on empirical observations of commercial raspberry in western Argentina. To assess the effects of pollination intensity for fruit production, we conducted simulations over a range of visit number per flower by the two primary managed pollinators worldwide, Apis mellifera and Bombus terrestris. Simulations identified that ~15-35 visits per flower by A.mellifera or ~10-20 visits by B.terrestris provide adequate pollination and maximize raspberry fruit quality (i.e., estimated as the proportion of ovules that develop into drupelets). Visits in excess of these optima reduce simulated fruit quality, and flowers receiving >670 honey bee visits or >470 bumble bee visits would produce fruits of poorer quality than those receiving no bee visits. The simulations generated consistent, unbiased predictions of fruit quality for 12 raspberry fields. This model could be adapted easily to other animal-pollinated crops and used to guide efficient pollinator management in any agro-ecosystem.

Florivory indirectly decreases the plant reproductive output through changes in pollinator attraction.

Species often interact indirectly with each other via their traits. There is increasing appreciation of trait‐mediated indirect effects linking multiple interactions. Flowers interact with both pollinators and floral herbivores, and the flower‐pollinator interaction may be modified by indirect effects of floral herbivores (i.e., florivores) on flower traits such as flower size attracting pollinators. To explore whether flower size affects the flower‐pollinator interaction, we used Eurya japonica flowers. We examined whether artificial florivory decreased fruit and seed production, and also whether flower size affected florivory and the number of floral visitors. The petal removal treatment (i.e., artificial florivory) showed approximately 50% reduction in both fruit and seed set in natural pollination but not in artificial pollination. Furthermore, flower size increased the number of floral visitors, although it did not affect the frequency of florivory. Our results demonstrate that petal removal indirectly decreased 75% of female reproductive output via decreased flower visits by pollinators and that flower size mediated indirect interactions between florivory and floral visitors.

Natural partners: a didactic proposal to understand the relevance of the mutualistic flower-pollinator interaction

Pollination by animals is a key process involved in flowering plants reproduction. In the educational context, this topic is rarely addressed from the plant-pollinator interaction point of view, and its importance is poorly recognized by the students. Here we present a didactic proposal developed to address the sexual reproduction in plants, based on the plant-pollinator mutualistic association. The sequence of activities developed includes the display of a video, observation and handling of flowers and fruits, as well as play activities where the pollination process and the correspondence between certain flower traits and pollinators are represented. The set of questions applied suggests a change or improvement in students knowledge about the contents after the activities.

Flower Pollinator Interactions within Two Tropical Tree Species of Mizoram, North East India

Understanding the interactions between plants and pollinators is vital in exploring the structural and functional dynamics of tropical forest ecosystem. Such interactions are also helpful in resolving issues of regeneration, maintenance of biodiversity and conservation of tropical forest resources. The aim of this study was to understand the foraging behaviour of floral visitors of two valuable forest species in North East India, viz. Schima wallichii Choisy and Lagerstroemia speciosa (L.) Pers. The types and behaviour of pollinators were assessed by counting of the total number of visits by insects during day time (05:00-18:00) per field visit/flower in the peak flowering season, foraging rate (number of flowers visited/minutes) and average time spent per flower. The frequency of pollinator visits was also determined in terms of visits/flower/hour. Ten species belonging to seven families were recorded visiting S. wallichii flowers. The flowers of L. speciosa were mainly visited by three species in the family Apidae and one species in the family Calliphoridae. Various moth and bee species were involved in pollination of S. wallichii flowers. The Xylcopa spp. of bee showed a high level of functional synchronisation with the floral morphology of L. speciosa.

Flower Pollinator Interactions within Two Tropical Tree Species of Mizoram, North East India

Understanding the interactions between plants and pollinators is vital in exploring the structural and functional dynamics of tropical forest ecosystem. Such interactions are also helpful in resolving issues of regeneration, maintenance of biodiversity and conservation of tropical forest resources. The aim of this study was to understand the foraging behaviour of floral visitors of two valuable forest species in North East India, viz. Schima wallichii Choisy and Lagerstroemia speciosa (L.) Pers. The types and behaviour of pollinators were assessed by counting of the total number of visits by insects during day time (05:00-18:00) per field visit/flower in the peak flowering season, foraging rate (number of flowers visited/minutes) and average time spent per flower. The frequency of pollinator visits was also determined in terms of visits/flower/hour. Ten species belonging to seven families were recorded visiting S. wallichii flowers. The flowers of L. speciosa were mainly visited by three species in the family Apidae and one species in the family Calliphoridae. Various moth and bee species were involved in pollination of S. wallichii flowers. The Xylcopa spp. of bee showed a high level of functional synchronisation with the floral morphology of L. speciosa.

Pollinator-mediated selection on nectary depth in Urophysa (Ranunculaceae)

Pollinator-mediated selection has been considered to be one of major factors that shapes the evolution of flowers by matching flowers to their pollinators on traits associated with attraction of pollinators or mechanical fit. The match between nectary depth, which means the length of the tubular structure formed in many plant species to hide the nectary and store nectar, and the mouthparts length of its major nectar-foraging pollinators has been repeatedly demonstrated as an example, because this trait have shown a positive relationship with pollen removal and deposition in experimental manipulations in many synpetalous plants and orchid family. However, it remains unclear how pollinator-mediated selection affects the evolution of nectary depth in choripetalous and actinomorphic flowers, such as most flowers in Ranunculaceae. Here we investigated floral characteristics and pollinators in Urophysa rockii Ulbr. and U. henryi (Oliv.) Ulbr., as they are quite the same in habitat, anthesis and morphological characteristics except for nectary depth. Both of these species have flat white sepals and yellow petals each has a spatial structure at the base that contains nectar, but the nectary depth of U. rockii is deeper than that of U. henryi, for the former petals are shortly spurred about 3-4 mm in length while the latter are saccate. Meanwhile, the flowers of both species are most frequently visited by Apis cerana, the Chinese honey bee, and one or two species of hover fly, Syrphidae, but only A. cerana was able to forage nectar in U. rockii while all visitors can forage nectar in U. henryi. A. cerana always lands on the center of a flower and projects its proboscis into each petal when its thorax touches anthers and stigmas. The difference between two species is that U. rockii was visited by A. cerana with a higher frequency, longer visiting time per flower and more activities on flowers than U. henryi. Besides, the petal width and its nectary depth of U. rockii closely match the width of the labrum and the effective mouthparts length of A. cerana, respectively. Therefore, we concluded that pollinator-mediated selection played a vital role in the evolution of nectary depth in Urophysa, with deeper nectaries favoured through reproductive fitness, because this trait affects flower-pollinator interaction and therefore pollen deposition. We also detected deeper nectaries favoured because this trait also affects nectar accumulation as well as deeper nectaries can prevent inefficiency visitors from foraging nectar effectively.

Flavonols drive plant microevolution

The idea that pollinators are in large part responsible for the diversity of flowering plants dates back more than 150 years to Darwin's work, but even modern scientists have struggled to identify specific 'speciation genes' and determine how they influenced flower-pollinator interactions. A new study proposes that a series of mutations in a single gene controlling floral chemicals influenced pollinator preferences, likely resulting in speciation, bringing us closer to finding a speciation gene.

Flowering Phenology and Observations on the Pollination Biology of South American Cacti. 1.Denmoza rhodacantha

Summary: Pollination biology is an especially important component of the overall ecological setting of a plant species since it has direct implications on reproductive success. Over time, a typological approach to classifying flower—pollinator interactions in the form of “floral syndromes” has been developed, and considerable predictive power is traditionally ascribed to these syndromes. Recent studies have increasingly questioned both the predictive value of the syndrome concept, as well as the underlying notion of increasing specialization amongst flower-pollinator interactions. The casual discovery that the seemingly ornithophilous flowers of the globose to shortly columnar South American cactus Denmoza rhodacantha (Cactaceae: Cactoideae: Cereeae: Trichocereinae) are visited by solitary pollen-collecting halictid bees, rather than the expected hummingbirds, adds another example to the growing body of mismatches between floral syndrome and observed pollinator.

Heterostyly accelerates diversification via reduced extinction in primroses.

The exceptional species diversity of flowering plants, exceeding that of their sister group more than 250-fold, is especially evident in floral innovations, interactions with pollinators and sexual systems. Multiple theories, emphasizing flower-pollinator interactions, genetic effects of mating systems or high evolvability, predict that floral evolution profoundly affects angiosperm diversification. However, consequences for speciation and extinction dynamics remain poorly understood. Here, we investigate trajectories of species diversification focusing on heterostyly, a remarkable floral syndrome where outcrossing is enforced via cross-compatible floral morphs differing in placement of their respective sexual organs. Heterostyly evolved at least 20 times independently in angiosperms. Using Darwin's model for heterostyly, the primrose family, we show that heterostyly accelerates species diversification via decreasing extinction rates rather than increasing speciation rates, probably owing to avoidance of the negative genetic effects of selfing. However, impact of heterostyly appears to differ over short and long evolutionary time-scales: the accelerating effect of heterostyly on lineage diversification is manifest only over long evolutionary time-scales, whereas recent losses of heterostyly may prompt ephemeral bursts of speciation. Our results suggest that temporal or clade-specific conditions may ultimately determine the net effects of specific traits on patterns of species diversification.

Fine-tuned Bee-Flower Coevolutionary State Hidden within Multiple Pollination Interactions

Relationships between flowers and pollinators are generally considered cases of mutualism since both agents gain benefits. Fine-tuned adaptations are usually found in the form of strict one-to-one coevolution between species. Many insect pollinators are, however, considered generalists, visiting numerous kinds of flowers, and many flower species (angiosperms) are also considered generalists, visited by many insect pollinators. We here describe a fine-tuned coevolutionary state of a flower-visiting bee that collects both nectar and pollen from an early spring flower visited by multiple pollinators. Detailed morphology of the bee proboscis is shown to be finely adjusted to the floral morphology and nectar production of the flower. Behavioral observations also confirm the precision of this mutualism. Our results suggest that a fine-tuned one-to-one coevolutionary state between a flower species and a pollinator species might be common, but frequently overlooked, in multiple flower-pollinator interactions.

Floral epidermal structure and flower orientation: getting to grips with awkward flowers

The petal epidermis has been found to be important in mediating flower-pollinator interactions. Structures produced on the petal surface, in particular cone-shaped papillate (or conical) cells, have been shown to enhance bumblebee preference for flowers. One reason for this increase in preference is that the conical cells facilitate efficient handling of flowers. This is particularly clear when flower architecture requires bees to land on a vertical surface. We therefore tested the hypothesis that flowers that are held vertically show a greater tendency to produce conical cells. Analysis of 183 species finds that there is no significant relationship between the structures on the petal surface and flower orientation. We discuss the multifunctional properties of conical cells and other floral surface structures that may mean that other factors are of equal or greater importance in the relationship between pollinators and petal epidermal form.