Effects of nectar robbing on nectar dynamics and bumblebee foraging strategies inLinaria vulgaris(Scrophulariaceae)

Floral visitors of sesame (Sesamum indicum L.): Elucidating their nectar-robbing behaviour and impacts on the plant reproduction

Nectar robbing is common in angiosperms, especially in long tubular flowers or flowers with spurs that keep nectar out of reach of visitors. However, the robbing behaviour of bees is less understood. Here, we studied the sesame visitors, their robbing behaviour, and the impacts of robbing on plant reproductive fitness. Diverse insect species (primarily members of Hymenoptera) visited sesame flowers. The most effective pollinators were Amegilla zonata, Apis cerana, Apis dorsata, Apis florea, Ceratina binghami, Halictus acrocephalus and Xylocopa amethystina. Almost all visitors with variable percentages revealed the nectar-robbing phenomenon. Robbing activity depended on a complex of multiple attributes, including the visitor's body size, the corolla tube length, the availability and accessibility of nectar, and the resource-collecting task allocation of bees. Robbing activity varied according to flower-visiting species, flowering period and daytime. Robbing was comparatively higher in the late flowering period at 10.00-14.00 h. In the case of robbing visits, flower handling time was lower, and the visitation rate remained higher than non-robbing visits. Robbing visits did not significantly affect fruit and seed sets of sesame. Therefore, we can interpret the nectar-robbing interactions on sesame as commensal, with pollinators benefitting without altering the plant's reproductive fitness.

The genome sequence of the common toadflax, Linaria vulgaris Mill., 1768

We present a genome assembly from a Linaria vulgaris specimen (common toadflax; Streptophyta; Magnoliopsida; Lamiales; Plantaginaceae). The genome sequence is 760.5 megabases in span. Most of the assembly is scaffolded into six chromosomal pseudomolecules. Two mitochondrial genomes were assembled, which were 330.8 and 144.0 kilobases long. The plastid genome was also assembled and is 156.7 kilobases in length.

Breeding System and Response of the Pollinator to Floral Larceny and Florivory Define the Reproductive Success in Aerides odorata

Consumption of pollination reward by felonious means in a plant species can influence the foraging behavior of its pollinator and eventually the reproductive success. So far, studies on this aspect are largely confined to interaction involving plant-pollinators and nectar robbers or thieves. However, a foraging guild in such interactions may also include floral herbivores or florivores. There is a paucity of information on the extent to which nectar larcenists may influence the foraging behavior of the pollinator and reproductive fitness of plants in the presence of a florivore. We investigated various forms of larceny in the natural populations of Aerides odorata, a pollinator-dependent and nectar-rewarding orchid. These populations differed in types of foraging guild, the extent of larceny (thieving/robbing), which can occur with or without florivory, and natural fruit-set pattern. The nectariferous spur of the flower serves as an organ of interest among the foraging insects. While florivory marked by excision of nectary dissuades the pollinator, nectar thieving and robbing significantly enhance visits of the pollinator and fruit-set. Experimental pollinations showed that the species is a preferential outbreeder and experiences inbreeding depression from selfing. Reproductive fitness of the orchid species varies significantly with the extent of floral larceny. Although nectar thieving or robbing is beneficial in this self-compatible species, the negative effects of florivory were stronger. Our findings suggest that net reproductive fitness in the affected plant species is determined by the overarching effect of its breeding system on the overall interacting framework of the foraging guild.

Honeybees with extensive foraging experience rob nectar more frequently

Not all flower-visiting animals act as pollinators; some visitors engage in foraging nectar without pollen transfer. The tendency to rob nectar is related to visitors' morphological traits and rewards per foraging effort, and drivers of this variation within visitor species are largely unknown. Because foraging behavior is affected by foraging experience, we focused on the relationship between the tendency to rob nectar and the foraging experience of each forager. We investigated five consecutive visits of European honeybee, Apis mellifera L., on comfrey, Symphytum officinale L., in Japan. We estimated the foraging experience of A. mellifera using wing wear, categorized into six groups. Approximately 60% and 40% of A. mellifera foragers engaged in legitimate visits and nectar robbing, respectively. Moreover, most A. mellifera engaged in only one foraging tactic. The proportion of nectar robbing was related to wing wear and was higher in individuals with extensively damaged wings than those with less damaged wings. The present study suggests that extensively experienced honeybee foragers tend towards nectar robbing.

Behavioural responses by a bumble bee to competition with a niche-constructing congener

While feeding, foragers can alter their environment. Such alteration constitutes ecological niche construction (ENC) if it enables future benefits for the constructor and conspecific individuals. The environmental modification may also affect non‐constructing, bystander species, especially if they share resources with constructor species. If so, ENC could confer the constructor species a competitive advantage by both enhancing its foraging returns and reducing those of bystander species.

Expectations – (E1) ENC frequency should vary positively with the recent and current density of the constructor species, and (E2) constructors should use modifications disproportionately. In contrast, bystanders should (E3) experience intensified competition for the affected resource, and (E4) exhibit diverse, possibly mitigating, responses to ENC, depending on opportunity and relative benefits.

We investigated these expectations in Argentina for competition for Fuchsia magellanica nectar between an invasive bumble bee Bombus terrestris (terr: putative constructor), which often bites holes at the bases of floral tubes to rob nectar, and native B. dahlbomii (dahl: bystander), which normally accesses Fuchsia nectar through the flower mouth (front visits). Robbing holes constitute ENC, as they persist until the 7‐day flowers wilt. The dynamics of the incidence of robbed flowers, abundance of both bees and the number and types of their flower visits (front or robbing) were characterised by alternate‐day surveys of plants during 2.5 months.

After initially accessing Fuchsia nectar via front visits, terr switched to robbing and its abundance on Fuchsia increased 20‐fold within 10 days (E2). Correspondingly, the incidence of robbed flowers varied positively with recent and past terr abundance (E1). In contrast, dahl abundance remained low and varied negatively with the incidence of robbed flowers (E3). When terr ceased visiting Fuchsia, dahl abundance increased sixfold within 10 days (E3), possibly because many dahl previously had avoided competition with terr by feeding on other plant species (E4). While terr was present, dahl on Fuchsia used front visits (tolerance) or used existing robbing holes (adoption: E4). The diverse dahl responses suggest partial compensation for competition with terr.

ENC alters competitive asymmetry, favouring constructor species. However, bystander responses can partially offset this advantage, perhaps facilitating coexistence.

The Sensory and Cognitive Ecology of Nectar Robbing

Animals foraging from flowers must assess their environment and make critical decisions about which patches, plants, and flowers to exploit to obtain limiting resources. The cognitive ecology of plant-pollinator interactions explores not only the complex nature of pollinator foraging behavior and decision making, but also how cognition shapes pollination and plant fitness. Floral visitors sometimes depart from what we think of as typical pollinator behavior and instead exploit floral resources by robbing nectar (bypassing the floral opening and instead consuming nectar through holes or perforations made in floral tissue). The impacts of nectar robbing on plant fitness are well-studied; however, there is considerably less understanding, from the animal’s perspective, about the cognitive processes underlying nectar robbing. Examining nectar robbing from the standpoint of animal cognition is important for understanding the evolution of this behavior and its ecological and evolutionary consequences. In this review, we draw on central concepts of foraging ecology and animal cognition to consider nectar robbing behavior either when individuals use robbing as their only foraging strategy or when they switch between robbing and legitimate foraging. We discuss sensory and cognitive biases, learning, and the role of a variable environment in making decisions about robbing vs. foraging legitimately. We also discuss ways in which an understanding of the cognitive processes involved in nectar robbing can address questions about how plant-robber interactions affect patterns of natural selection and floral evolution. We conclude by highlighting future research directions on the sensory and cognitive ecology of nectar robbing.

Corolla Abscission Triggered by Nectar Robbers Positively Affects Reproduction by Enhancing Self-Pollination in Symphytum officinale (Boraginaceae)

Simple Summary

Nectar robbers affect plant fitness in different degrees and in different ways, potentially constituting an important part of pollination interactions. While the negative effects of nectar robbing on plant reproductive success have been widely reported, the positive effects are quite unclear. Hence, our study was designed to assess the effects of nectar robbers on reproductive success of Symphytum officinale. This will help in understanding the evolutionary significance of mutualistic relationships between plants and their visitors.

Abstract

Nectar robbers, which affect plant fitness (directly or indirectly) in different degrees and in different ways, potentially constitute a significant part of mutualistic relationships. While the negative effects of nectar robbing on plant reproductive success have been widely reported, the positive effects remain unknown. The target of our study was to evaluate the effects of nectar robbers on the reproductive success of Symphytum officinale (Boraginaceae). We observed the behavior, species and times of visitors in the field, and we assessed the effect of nectar robbers on corolla abscission rate and time. To test the fitness of corolla abscission, we detected the changes in stigma receptivity, pollen viability, pollen amount and appendage opening size along with the time of flower blossom. The flowering dynamics and floral structure were observed to reveal the mechanism of self-pollination. Finally, pollen deposition seed set rate and fruit set rate were determined to estimate the effect of nectar robbers on reproduction success. We observed 14 species of visitors and 2539 visits in 50 h of observation; 91.7% of them were nectar robbers. The pressure and nectar removal of nectar robbers significantly promoted corolla abscission during a period when pollen grains are viable and the stigma is receptive. In addition, corolla abscission significantly increased the pollen deposition and seed setting rate. Our results demonstrate that nectar robbing contributes to enhancing seed production and positively and indirectly impacts the reproductive success of S. officinale. This mechanism involved the movement of anthers and indirect participation by nectar robbers, which was rarely investigated. Considering the multiple consequences of nectar robbing, understanding the impact of nectar robbers on plant reproduction is essential to comprehend the evolutionary importance of relationships between plants and their visitors.

Flower evolution in the presence of heterospecific gene flow and its contribution to lineage divergence

The success of species depends on their ability to exploit ecological resources in order to optimize their reproduction. However, species are not usually found within single-species ecosystems but in complex communities. Because of their genetic relatedness, closely related lineages tend to cluster within the same ecosystem, rely on the same resources, and be phenotypically similar. In sympatry, they will therefore compete for the same resources and, in the case of flowering plants, exchange their genes through heterospecific pollen transfer. These interactions, nevertheless, pose significant challenges to species co-existence because they can lead to resource limitation and reproductive interference. In such cases, divergent selective pressures on floral traits will favour genotypes that isolate or desynchronize the reproduction of sympatric lineages. The resulting displacement of reproductive characters will, in turn, lead to pre-mating isolation and promote intraspecific divergence, thus initiating or reinforcing the speciation process. In this review, we discuss the current theoretical and empirical knowledge on the influence of heterospecific pollen transfer on flower evolution, highlighting its potential to uncover the ecological and genomic constraints shaping the speciation process.

Nectar robbing in bellflower (Sesamum radiatum) benefited pollinators but unaffected maternal function of plant reproduction

Nectar robbing – foraging nectar illegitimately – has negative, neutral, or positive effects on maternal function of plant reproduction and/or on pollinators. It has been suggested that nectar robbing has a non-negative effect on maternal function of plant reproduction in autogamous and mixed breeding plants; however this hypothesis requires deeper understanding with more studies. We investigated the impact of natural nectar robbing on maternal function of plant reproduction and visitation characteristics of pollinators in Sesamum radiatum, an autogamous plant. Pollinators were observed on unrobbed open flowers and robbed open flowers. In robbed flowers, pollinators’ visit type and foraging time were examined. The seed sets of these flower types were examined. Xylocopa latipes was both a primary robber and a legitimate pollinator, X. bryorum was an exclusive primary robber, and Megachile disjuncta was a cosmopolitan pollinator. In robbed flowers, most of the pollinators foraged mostly as secondary nectar robbers. The foraging time shortened considerably when pollinators robbed nectar – a positive effect on pollinators’ foraging efficiency. Robbing did not negatively affect seed set – a neutral effect on the plant’s reproduction. Our study agrees that nectar robbing might have a non-negative effect on reproduction in autogamous and mixed breeding plants.

Evolutionary ecology of nectar

Background

Floral nectar is an important determinant of plant-pollinator interactions and an integral component of pollination syndromes, suggesting it is under pollinator-mediated selection. However, compared to floral display traits, we know little about the evolutionary ecology of nectar. Combining a literature review with a meta-analysis approach, we summarize the evidence for heritable variation in nectar traits and link this variation to pollinator response and plant fitness. We further review associations between nectar traits and floral signals and discuss them in the context of honest signalling and targets of selection.

Scope

Although nectar is strongly influenced by environmental factors, heritable variation in nectar production rate has been documented in several populations (mean h2 = 0.31). Almost nothing is known about heritability of other nectar traits, such as sugar and amino acid concentrations. Only a handful of studies have quantified selection on nectar traits, and few find statistically significant selection. Pollinator responses to nectar traits indicate they may drive selection, but studies tying pollinator preferences to plant fitness are lacking. So far, only one study conclusively identified pollinators as selective agents on a nectar trait, and the role of microbes, herbivores, nectar robbers and abiotic factors in nectar evolution is largely hypothetical. Finally, there is a trend for positive correlations among floral cues and nectar traits, indicating honest signalling of rewards.

Conclusions

Important progress can be made by studies that quantify current selection on nectar in natural populations, as well as experimental approaches that identify the target traits and selective agents involved. Signal-reward associations suggest that correlational selection may shape evolution of nectar traits, and studies exploring these more complex forms of natural selection are needed. Many questions about nectar evolution remain unanswered, making this a field ripe for future research.

Micromorphological and histochemical attributes of flowers and floral reward in Linaria vulgaris (Plantaginaceae)

The self-incompatible flowers of Linaria vulgaris have developed a range of mechanisms for attraction of insect visitors/pollinators and deterrence of ineffective pollinators and herbivores. These adaptive traits include the flower size and symmetry, the presence of a spur as a "secondary nectar presenter," olfactory (secondary metabolites) and sensual (scent, flower color, nectar guide-contrasting palate) signals, and floral rewards, i.e. pollen and nectar. Histochemical tests revealed that the floral glandular trichomes produced essential oils and flavonoids, and pollen grains contained flavonoids, terpenoids, and steroids, which play a role of olfactory attractants/repellents. The nectary gland is disc-shaped and located at the base of the ovary. Nectar is secreted through numerous modified stomata. Nectar secretion began in the bud stage and lasted to the end of anthesis. The amount of produced nectar depended on the flower age and ranged from 0.21 to 3.95 mg/flower (mean = 1.51 mg). The concentration of sugars in the nectar reached up to 57.0%. Both the nectar amount and sugar concentration demonstrated a significant year and population effect. Pollen production was variable between the years of the study. On average, a single flower of L. vulgaris produced 0.31 mg of pollen. The spectrum of insect visitors in the flowers of L. vulgaris differed significantly between populations. In the urban site, Bombus terrestris and Apis mellifera were the most common visitors, while a considerable number of visits of wasps and syrphid flies were noted in the rural site.

Costs and benefits of alternative food handling tactics help explain facultative exploitation of pollination mutualisms

Many mutualisms are taken advantage of by organisms that take rewards from their partners but provide no benefit in return. In the absence of traits that limit exploitation, facultative exploiters (partners that can either exploit or cooperate) are widely predicted by mutualism theory to choose an exploitative strategy, potentially threatening mutualism stability. However, it is unknown whether facultative exploiters choose to exploit, and, if so, make this choice because it is the most beneficial strategy for them. We explored these questions in a subalpine plant-insect community in which individuals of several bumble bee species visit flowers both "legitimately" (entering via the flower opening, picking up and depositing pollen, and hence behaving mutualistically) and via nectar robbing (creating holes through corollas or using an existing hole, bypassing stigmas and anthers). We applied foraging theory to (1) quantify handling costs, benefits and foraging efficiencies incurred by three bumble bee species as they visited flowers legitimately or robbed nectar in cage experiments, and (2) determine whether these efficiencies matched the food handling tactics these bee species employed in the field. Relative efficiencies of legitimate and robbing tactics depended on the combination of bee and plant species. In some cases (Bombus mixtus visiting Corydalis caseana or Mertensia ciliata), the robbing tactic permitted more efficient nectar removal. As both mutualism and foraging theory would predict, in the field, B. mixtus visiting C. caseana were observed more frequently robbing than foraging legitimately. However, for Bombus flavifrons visiting M. ciliata, the expectation from mutualism theory did not hold: legitimate visitation was the more efficient tactic. Legitimate visitation to M. ciliata was in fact more frequently observed in free-flying B. flavifrons. Free-flying B. mixtus also frequently visited M. ciliata flowers legitimately. This may reflect lower nectar volumes in robbed than unrobbed flowers in the field. These results suggest that a foraging ecology perspective is informative to the choice of tactics facultative exploiters make. In contrast, the simple expectation that exploiters should always have an advantage, and hence could threaten mutualism persistence unless they are deterred or punished, may not be broadly applicable.

The behavioral ecology of nectar robbing: why be tactic constant?

How do animals forage for variable food resources? For animals foraging at flowers, floral constancy has provided a framework for understanding why organisms visit some flowers while bypassing others. We extend this framework to the flower-handling tactics that visitors employ. Nectar robbers remove nectar through holes bitten in flowers, often without pollinating. Many foragers can switch between robbing and visiting flowers legitimately to gain access to nectar. We document that even though individuals can switch foraging tactics, they often do not. We explore whether individuals exhibit constancy to either robbing or visiting legitimately, which we term tactic constancy. We then extend hypotheses of floral constancy to understand when and why visitors exhibit tactic constancy and raise questions for future research.

Nectar replenishment maintains the neutral effects of nectar robbing on female reproductive success of Salvia przewalskii (Lamiaceae), a plant pollinated and robbed by bumble bees

Background and Aims

It has been suggested that the dynamics of nectar replenishment could differ for flowers after being nectar robbed or visited legitimately, but further experimental work is needed to investigate this hypothesis. This study aimed to assess the role of nectar replenishment in mediating the effects of nectar robbing on pollinator behaviour and plant reproduction.

Methods

Plant-robber-pollinator interactions in an alpine plant, Salvia przewalskii , were studied. It is pollinated by long-tongued Bombus religiosus and short-tongued B. friseanus , but robbed by B. friseanus . Nectar production rates for flowers after they were either robbed or legitimately visited were compared, and three levels of nectar robbing were created to detect the effects of nectar robbing on pollinator behaviour and plant reproduction.

Key Results

Nectar replenishment did not differ between flowers that had been robbed or legitimately visited. Neither fruit set nor seed set was significantly affected by nectar robbing. In addition, nectar robbing did not significantly affect visitation rate, flowers visited within a plant per foraging bout, or flower handling time of the legitimate pollinators. However, a tendency for a decrease in relative abundance of the pollinator B. religiosus with an increase of nectar robbing was found.

Conclusions

Nectar robbing did not affect female reproductive success because nectar replenishment ensures that pollinators maintain their visiting activity to nectar-robbed flowers. Nectar replenishment might be a defence mechanism against nectar robbing to enhance reproductive fitness by maintaining attractiveness to pollinators. Further studies are needed to reveal the potential for interference competition among bumble bees foraging as robbers and legitimate visitors, and to investigate variation of nectar robbing in communities with different bumble bee species composition.

Pollen Deposition Is More Important than Species Richness for Seed Set in Luffa Gourd

In the context of global biodiversity decline, it is imperative to understand the different aspects of bee communities for sustaining the vital ecosystem service of pollination. Bee species can be assigned to functional groups (average difference among species in functionally related traits) on the basis of complementarity (trait variations exhibited by individual organisms) in their behavior but is not yet known which functional group trait is most important for seed set. In this study, first, the functional groups of bees were made based on their five selected traits (pollen deposition, visitation rate, stay time, visiting time of the day, body size) and then related to the seed set of obligate cross-pollinated Luffa gourd (Luffa aegyptiaca). We found that bee diversity and abundance differed significantly among the studied plots, but only the bee species richness was positively related to the seed set. Functional group diversity in terms of pollen deposition explained even more of the variance in seed set (r ² = 0.74) than did the species richness (r ² = 0.53) making it the most important trait of bee species for predicting the crop reproductive success.

Pollen-mediated gene flow from transgenic cotton under greenhouse conditions is dependent on different pollinators

With the large-scale release of genetically modified (GM) crops, there are ecological concerns on transgene movement from GM crops to non-GM counterparts and wild relatives. In this research, we conducted greenhouse experiments to measure pollen-mediated gene flow (PGF) in the absence and presence of pollinators (Bombus ignitus, Apis mellifera and Pieris rapae) in one GM cotton (resistant to the insect Helicoverpa armigera and the herbicide glyphosate) and two non-GM lines (Shiyuan321 and Hai7124) during 2012 and 2013. Our results revealed that: (1) PGF varied depending on the pollinator species, and was highest with B. ignitus (10.83%) and lowest with P. rapae (2.71%); (2) PGF with B. ignitus depended on the distance between GM and non-GM cottons; (3) total PGF to Shiyuan321 (8.61%) was higher than to Hai7124 (4.10%). To confirm gene flow, we tested hybrids carrying transgenes for their resistance to glyphosate and H. armigera, and most hybrids showed strong resistance to the herbicide and insect. Our research confirmed that PGF depended on pollinator species, distance between plants and the receptor plant.

Corolla morphology influences diversification rates in bifid toadflaxes (Linaria sect. Versicolores)

BACKGROUND AND AIMS

The role of flower specialization in plant speciation and evolution remains controversial. In this study the evolution of flower traits restricting access to pollinators was analysed in the bifid toadflaxes (Linaria sect. Versicolores), a monophyletic group of ~30 species and subspecies with highly specialized corollas.

METHODS

A time-calibrated phylogeny based on both nuclear and plastid DNA sequences was obtained using a coalescent-based method, and flower morphology was characterized by means of morphometric analyses. Directional trends in flower shape evolution and trait-dependent diversification rates were jointly analysed using recently developed methods, and morphological shifts were reconstructed along the phylogeny. Pollinator surveys were conducted for a representative sample of species.

KEY RESULTS

A restrictive character state (narrow corolla tube) was reconstructed in the most recent common ancestor of Linaria sect. Versicolores. After its early loss in the most species-rich clade, this character state has been convergently reacquired in multiple lineages of this clade in recent times, yet it seems to have exerted a negative influence on diversification rates. Comparative analyses and pollinator surveys suggest that the narrow- and broad-tubed flowers are evolutionary optima representing divergent strategies of pollen placement on nectar-feeding insects.

CONCLUSIONS

The results confirm that different forms of floral specialization can lead to dissimilar evolutionary success in terms of diversification. It is additionally suggested that opposing individual-level and species-level selection pressures may have driven the evolution of pollinator-restrictive traits in bifid toadflaxes.

Floral nectar guide patterns discourage nectar robbing by bumble bees

Floral displays are under selection to both attract pollinators and deter antagonists. Here we show that a common floral trait, a nectar guide pattern, alters the behavior of bees that can act opportunistically as both pollinators and as antagonists. Generally, bees access nectar via the floral limb, transporting pollen through contact with the plant’s reproductive structures; however bees sometimes extract nectar from a hole in the side of the flower that they or other floral visitors create. This behavior is called “nectar robbing” because bees may acquire the nectar without transporting pollen. We asked whether the presence of a symmetric floral nectar guide pattern on artificial flowers affected bumble bees’ (Bombus impatiens) propensity to rob or access nectar “legitimately.” We discovered that nectar guides made legitimate visits more efficient for bees than robbing, and increased the relative frequency of legitimate visits, compared to flowers lacking nectar guides. This study is the first to show that beyond speeding nectar discovery, a nectar guide pattern can influence bees’ flower handling in a way that could benefit the plant.

Behavioural differences between male and female carpenter bees in nectar robbing and its effect on reproductive success in Glechoma longituba (Lamiaceae)

Male and female nectar robbers may show significantly different behaviour on host plants and thus have different impacts on reproductive fitness of the plants. A 4-year study in natural populations of Glechoma longituba has shown that male carpenter bees (Xylocopa sinensis) are responsible for most of the nectar robbing from these flowers, while female bees account for little nectar robbing, demonstrating distinct behavioural differentiation between male and female bees in visiting flowers. The smaller male bee spends less time visiting a single flower than the larger female bee, consequently, the male bee is capable of visiting more flowers per unit time and has a higher foraging efficiency. Moreover, the robbing behaviour of female carpenter bees is more destructive and affects flower structures (ovules and nectaries) and floral life-span more than that of the male bee. According to the energy trade-off hypothesis, the net energy gain for male bees during nectar robbing greatly surpasses energy payout (17.72 versus 2.43 J), while the female bee net energy gain is barely adequate to meet energy payout per unit time (3.78 versus 2.39 J). The differences in net energy gain for male and female bees per unit time in nectar robbing are the likely cause of observed behavioural differences between the sexes. The differences in food resource preference between male and female bees constitute an optimal resource allocation pattern that enables the visitors to utilise floral resources more efficiently.

Differential effects of nectar robbing by the same bumble-bee species on three sympatric Corydalis species with varied mating systems

BACKGROUND AND AIMS

Most research on the widespread phenomenon of nectar robbing has focused on the effect of the nectar robbers' behaviour on host-plant fitness. However, attention also needs be paid to the characteristics of host plants, which can potentially influence the consequences of nectar robbing as well. A system of three sympatric Corydalis species sharing the same nectar-robbing bumble-bee was therefore studied over 3 years in order to investigate the effect of nectar robbing on host reproductive fitness.

METHODS

Three perennial species of Corydalis were studied in the Shennongjia Mountain area, central China. Observations were conducted on visitor behaviour and visitation frequencies of nectar-robbers and legitimate pollinators.

KEY RESULTS

The results indicated that the effect of nectar robbing by Bombus pyrosoma varied among species, and the three species had different mating systems. Seed set was thus influenced differentially: there was no effect on seed set of the predominantly selfing C. tomentella; for the facultative outcrossing C. incisa, nectar robbing by B. pyrosoma had a positive effect; and nectar robbing had a significant negative effect on the seed set of outcrossing C. ternatifolia.

CONCLUSIONS

A hypothesis is proposed that the type of host-plant mating system could influence the consequences of nectar robbing on host reproductive fitness.

Predicting the effects of nectar robbing on plant reproduction: implications of pollen limitation and plant mating system

The outcome of species interactions is often difficult to predict, depending on the organisms involved and the ecological context. Nectar robbers remove nectar from flowers, often without providing pollination service, and their effects on plant reproduction vary in strength and direction. In two case studies and a meta-analysis, we tested the importance of pollen limitation and plant mating system in predicting the impacts of nectar robbing on female plant reproduction. We predicted that nectar robbing would have the strongest effects on species requiring pollinators to set seed and pollen limited for seed production. Our predictions were partially supported. In the first study, natural nectar robbing was associated with lower seed production in Delphinium nuttallianum, a self-compatible but non-autogamously selfing, pollen-limited perennial, and experimental nectar robbing reduced seed set relative to unrobbed plants. The second study involved Linaria vulgaris, a self-incompatible perennial that is generally not pollen limited. Natural levels of nectar robbing generally had little effect on estimates of female reproduction in L. vulgaris, while experimental nectar robbing reduced seed set per fruit but not percentage of fruit set. A meta-analysis revealed that nectar robbing had strong negative effects on pollen-limited and self-incompatible plants, as predicted. Our results suggest that pollination biology and plant mating system must be considered to understand and predict the ecological outcome of both mutualistic and antagonistic plant-animal interactions.

Corolla herbivory, pollination success and fruit predation in complex flowers: an experimental study with Linaria lilacina (Scrophulariaceae)

BACKGROUND AND AIMS

Herbivory on floral structures has been postulated to influence the evolution of floral traits in some plant species, and may also be an important factor influencing the occurrence and outcome of subsequent biotic interactions related to floral display. In particular, corolla herbivory may affect structures differentially involved in flower selection by pollinators and fruit predators (specifically, those ovopositing in ovaries prior to fruit development); hence floral herbivores may influence the relationships between these mutualistic and antagonistic agents.

METHODS

The effects of corolla herbivory in Linaria lilacina (Scrophulariaceae), a plant species with complex flowers, were considered in relation to plant interactions with pollinators and fruit predators. Tests were made as to whether experimentally created differences in flower structure (resembling those occurring naturally) may translate into differences in reproductive output in terms of fruit or seed production.

KEY RESULTS

Flowers with modified corollas, particularly those with lower lips removed, were less likely to be selected by pollinators than control flowers, and were less likely to be successfully visited and pollinated. As a consequence, fruit production was also less likely in these modified flowers. However, none of the experimental treatments affected the likelihood of visitation by fruit predators.

CONCLUSIONS

Since floral herbivory may affect pollinator visitation rates and reduce seed production, differences among plants in the proportion of flowers affected by herbivory and in the intensity of the damage inflicted on affected flowers may result in different opportunities for reproduction for plants in different seasons.