Variation in nectar volume and composition of Impatiens capensis at the individual,plant, and population levels

Although the volume and chemical composition of nectars are known to vary among plant species and to affect pollinator response to plants, relatively little is known of the variation in volume, and sugar and amino acid composition within species. We collected nectar from Impatiens capensis in a nested design: three flowers from each of three plants from each of three populations. This design enabled us to quantify variation within individual plants, among plants within populations, and among populations. Using high performance liquid chromatography, we analyzed the sugar and amino composition of the 27 flowers. Analysis of variance showed that none of the parameters (volume, concentrations of three sugars and 24 amino compounds) varied within individuals. Variation in nectar volume was not significant among plants but was nearly significant among populations. Of the three sugars detected (sucrose, glucose, and fructose), the only significant variation was that of sucrose among populations. Concentrations of 12 amino compounds varied significantly at the plant level while 7 amino compounds varied among populations. The results indicate that: (1) pooling of nectar samples from flowers of individual plants can be an acceptable methodology for those seeking to understand within species variation; (2) amino compounds appear to vary more than either volumes or sugar concentrations; (3) future studies should assess how much of the observed variation is due to genetic versus environmental differences; (4) additional studies should examine the geographic variation in nectar parameters and pollinators of I. capensis in order to assess the role different pollinators play in shaping nectar composition.     

Small but attractive: female‐biased nectar production and floral visitors in a dimorphic shrub

• In sexually dimorphic species, hermaphrodite flowers in gynodioecious species or male flowers in dioecious species are often larger and produce more nectar than their conspecific female flowers. As a consequence, hermaphrodite or male flowers frequently receive more pollinator visits.
• Sex ratio, flower size, floral display, nectar production and floral visits were evaluated in two natural populations of Fuchsia thymifolia, a morphologically gynodioecious but functionally subdioecious insect‐pollinated shrub.
• Sex ratio did not differ from the expected 1:1 in the two studied populations. As expected, hermaphrodite flowers were larger than female flowers, but in contrast to the general pattern, hermaphrodite flowers did not produce nectar or produced much less than female flowers. Flower visitors were flies (68%) and bumblebees (24%), both of which showed a preference for female flowers. No sex difference was detected in either flower longevity or floral display across the flowering season.
• Higher nectar production by females may attract more pollinators, and may be a strategy to enhance female reproductive success in this species. Finally, floral dimorphism and insect preferences did not seem to hamper the maintenance of sub‐dioecy or prevent the evolution of dioecy in F. thymifolia.

     

Plant–pollinator interactions and floral convergence in two species of <Emphasis Type="Italic">Heliconia</Emphasis> from the Caribbean Islands

Variation in interspecific interactions across geographic space is a potential driver of diversification and local adaptation. This study quantitatively examined variation in floral phenotypes and pollinator service of Heliconia bihai and H. caribaea across three Antillean islands. The prediction was that floral characters would correspond to the major pollinators of these species on each island. Analysis of floral phenotypes revealed convergence among species and populations of Heliconia from the Greater Antilles. All populations of H. caribaea were similar, characterized by long nectar chambers and short corolla tubes. In contrast, H. bihai populations were strongly divergent: on Dominica, H. bihai had flowers with short nectar chambers and long corollas, whereas on Hispaniola, H. bihai flowers resembled those of H. caribaea with longer nectar chambers and shorter corolla tubes. Morphological variation in floral traits corresponded with geographic differences or similarities in the major pollinators on each island. The Hispaniolan mango, Anthracothorax dominicus, is the principal pollinator of both H. bihai and H. caribaea on Hispaniola; thus, the similarity of floral phenotypes between Heliconia species suggests parallel selective regimes imposed by the principal pollinator. Likewise, divergence between H. bihai populations from Dominica and Hispaniola corresponded with differences in the pollinators visiting this species on the two islands. The study highlights the putative importance of pollinator-mediated selection as driving floral convergence and the evolution of locally-adapted plant variants across a geographic mosaic of pollinator species.     

Specialised protagonists in a plant–pollinator interaction: the pollination of Blumenbachia insignis (Loasaceae)

• Analyses of resource presentation, floral morphology and pollinator behaviour are essential for understanding specialised plant‐pollinator systems. We investigated whether foraging by individual bee pollinators fits the floral morphology and functioning of Blumenbachia insignis, whose flowers are characterised by a nectar scale‐staminode complex and pollen release by thigmonastic stamen movements.
• We described pollen and nectar presentation, analysed the breeding system and the foraging strategy of bee pollinators. We determined the nectar production pattern and documented variations in the longevity of floral phases and stigmatic pollen loads of pollinator‐visited and unvisited flowers.
• Bicolletes indigoticus (Colletidae) was the sole pollinator with females revisiting flowers in staminate and pistillate phases at short intervals, guaranteeing cross‐pollen flow. Nectar stored in the nectar scale‐staminode complex had a high sugar concentration and was produced continuously in minute amounts (~0.09 μl·h^?1). Pushing the scales outward, bees took up nectar, triggering stamen movements and accelerating pollen presentation. Experimental simulation of this nectar uptake increased the number of moved stamens per hour by a factor of four. Flowers visited by pollinators received six‐fold more pollen on the stigma than unvisited flowers, had shortened staminate and pistillate phases and increased fruit and seed set.
• Flower handling and foraging by Bicolletes indigoticus were consonant with the complex flower morphology and functioning of Blumenbachia insignis. Continuous nectar production in minute quantities but at high sugar concentration influences the pollen foraging of the bees. Partitioning of resources lead to absolute flower fidelity and stereotyped foraging behaviour by the sole effective oligolectic bee pollinator.

     

Relative effectiveness of insects versus hummingbirds as pollinators of Rubiaceae plants across elevation in Dominica,Caribbean

• Most angiosperms rely on animal pollination for reproduction, but the dependence on specific pollinator groups varies greatly between species and localities. Notably, such dependence may be influenced by both floral traits and environmental conditions. Despite its importance, their joint contribution has rarely been studied at the assemblage level.
• At two elevations on the Caribbean island of Dominica, we measured the floral traits and the relative contributions of insects versus hummingbirds as pollinators of plants in the Rubiaceae family. Pollinator importance was measured as visitation rate (VR) and single visit pollen deposition (SVD), which were combined to assess overall pollinator effectiveness (PE).
• In the wet and cool Dominican highland, we found that hummingbirds were relatively more frequent and effective pollinators than insects, whereas insects and hummingbirds were equally frequent and effective pollinators at the warmer and less rainy midelevation. Furthermore, floral traits correlated independently of environment with the relative importance of pollinators, hummingbirds being more important in plant species having flowers with long and wide corollas producing higher volumes of dilute nectar.
• Our findings show that both environmental conditions and floral traits influence whether insects or hummingbirds are the most important pollinators of plants in the Rubiaceae family, highlighting the complexity of plant–pollinator systems.

     

Pollination and breeding system of the enigmatic South African parasitic plant Mystropetalon thomii (Mystropetalaceae): rodents welcome,but not needed

• Unrelated plants adapted to particular pollinator types tend to exhibit convergent evolution in floral traits. However, inferences about likely pollinators from ‘pollination syndromes’ can be problematic due to trait overlap among some syndromes and unusual floral architecture in some lineages. An example is the rare South African parasitic plant Mystropetalon thomii (Mystropetalaceae), which has highly unusual brush‐like inflorescences that exhibit features of both bird and rodent pollination syndromes.
• We used camera traps to record flower visitors, quantified floral spectral reflectance and nectar and scent production, experimentally determined self‐compatibility and breeding system, and studied pollen dispersal using fluorescent dyes.
• The dark‐red inflorescences are usually monoecious, with female flowers maturing before male flowers, but some inflorescences are purely female (gynoecious). Inflorescences were visited intensively by several rodent species that carried large pollen loads, while visits by birds were extremely rare. Rodents prefer male‐ over female‐phase inflorescences, likely because of the male flowers’ higher nectar and scent production. The floral scent contains several compounds known to attract rodents. Despite the obvious pollen transfer by rodents, we found that flowers on both monoecious and gynoecious inflorescences readily set seed in the absence of rodents and even when all flower visitors are excluded.
• Our findings suggest that seed production occurs at least partially through apomixis and that M. thomii is not ecologically dependent on its rodent pollinators. Our study adds another species and family to the growing list of rodent‐pollinated plants, thus contributing to our understanding of the floral traits associated with pollination by non‐flying mammals.

     

Bees explain floral variation in a recent radiation of Linaria

The role of pollinators in floral divergence has long attracted the attention of evolutionary biologists. Although abundant studies have reported the effect of pollinators on flower‐shape variation and plant speciation, the influence of pollinators on plant species differentiation during rapid radiations and the specific consequences of shifts among similar pollinators are not well understood. Here, we evaluate the association between pollinators and floral morphology in a closely related and recently diversifying clade of Linaria species (sect. Supinae subsect. Supinae). Our approach combined pollinator observations, functional floral morphometric measures and phylogenetic comparative analyses. The fauna visiting Linaria species was determined by extensive surveys and categorized by a modularity algorithm, and the size and shape of flowers were analysed by means of standard and geometric morphometric measures. Standard measures failed to find relationships between the sizes of representative pollinators and flowers. However, discriminant function analyses of geometric morphometric data revealed that pollination niches are finer predictors of flower morphologies in Linaria if compared with phylogenetic relationships. Species with the most restrictive flowers displayed the most slender spurs and were pollinated by bees with larger proboscides. These restrictive flower shapes likely appeared more than once during the evolutionary history of the study group. We show that floral variation can be driven by shifts between pollinators that have been traditionally included in a single functional group, and discuss the consequences of such transitions for plant species differentiation during rapid radiations.     

Composition of the floral nectar of different subgenera of Argentinian Passiflora species

The composition of the floral nectar sugars and amino acids of four species of Passiflora (P. foetida, P. caerulea, P. suberosa, and P. misera) included in different infrageneric taxa and with distinct pollination mechanisms has been studied. The effect of weather and floral age on nectar volume, existence, and total and relative amounts of the various compounds was explored. The proportion of sugars was rather constant within a given species whereas the composition, number, and total quantity of amino acids showed great intraspecific and intra-plant variability; these nectar properties were independent of floral stage or meteorological conditions. Species belonging to the same subgenus displayed equivalent sugar ratios and similar total amount of amino acids, so these characteristics might be conservative in the genus. For all species, the amino acid concentration surpassed known values for their respective pollination syndromes, viz. bee and wasp-pollinated flowers. No relationship emerged between pollinators with different glossa length and nectars with distinct sugar ratios. Rather, nectar chemical composition seems to reflect taxonomic relationships.     

Extreme intraplant variation in nectar sugar composition in an insect-pollinated perennial herb

Variation in nectar chemistry among plants, flowers, or individual nectaries of a given species has been only rarely explored, yet it is an essential aspect to our understanding of how pollinator-mediated selection might act on nectar traits. This paper describes variation in nectar sugar composition in a population of the perennial herb Helleborus foetidus (Ranunculaceae) and dissects it into components due to variation among plants, flowers of the same plant, and nectaries of the same flower. The proportions of sucrose, glucose, and fructose in single-nectary nectar samples collected at two times in the flowering season were determined using high performance liquid chromatography (HPLC). Sugar composition varied extensively among nectaries, and nearly all combinations of individual sugars were recorded. Population-wide variance was mainly accounted for by variation among flowers of the same plant (56% of total), nectaries of the same flower (30%), and only minimally by differences among plants (14%). In absolute terms, intraplant variation was similar to or greater than that ordinarily reported in interspecific comparisons. Results suggest that the prevailing notion of intraspecific constancy in nectar sugar composition may be unwarranted for some species and that more elaborate nectar sampling designs are required to detect and appropriately account for extensive within-plant variance. Within-plant variation in nectar sugar composition will limit the ability of pollinators to exert selection on nectar chemistry in H. foetidus and may be advantageous to plants by reducing the number of flowers visited per foraging bout by variance-sensitive, risk-averse pollinators.     

Extranuptial nectaries in flowers: ants increase the reproductive success of the ant‐plant Miconia tococa (Melastomataceae)

• Although the production of extranuptial nectar is a common strategy of indirect defence against herbivores among tropical plants, the presence of extranuptial nectaries in reproductive structures is rare, especially in ant‐plants. This is because the presence of ants in reproductive organs can generate conflicts between the partners, as ants can inhibit the activity of pollinators or even castrate their host plants. Here we evaluate the hypothesis that the ant‐plant Miconia tococa produces nectar in its petals which attracts ants and affects fruit set.
• Floral buds were analysed using anatomical and histochemical techniques. The frequency and behaviour of floral visitors were recorded in field observations. Finally, an ant exclusion experiment was conducted to evaluate the effect of ant presence on fruit production.
• The petals of M. tococa have a secretory epidermis that produces sugary compounds. Nectar production occurred during the floral bud stage and attracted 17 species of non‐obligate ants (i.e. have a facultative association with ant‐plants). Ants foraged only on floral buds, and thus did not affect the activity of pollinators in the neighbouring open flowers. The presence of ants in the inflorescences increased fruit production by 15%.
• To our knowledge, the production of extranuptial nectar in the reproductive structures of a myrmecophyte is very rare, with few records in the literature. Although studies show conflicts between the partners in the ant–plant interaction, ants that forage on M. tococa floral buds protect the plant against floral herbivores without affecting bee pollination.

     

FLORAL NECTAR SUGAR COMPOSITION AND POLLINATOR TYPE AMONG NEW WORLD GENERA IN TRIBE ANTIRRHINEAE (SCROPHULARIACEAE)

The floral nectar sugar compositions of 20 New World species from 10 genera and of five interspecific hybrids in tribe Antirrhineae have been analyzed using high-performance liquid chromatography. Species are pollinated by short-tongued bees, long-tongued bees, and hummingbirds. Ornithophily represents the derived condition in the tribe and has arisen independently in subtribes Maurandyinae and Gambeliinae. All nectars analyzed are sucrose-dominant or -rich, except for the hexose-rich nectar of Mohavea breviflora. Despite the predominance of sucrose, floral nectar sugars from species pollinated by different pollen vectors have characteristic constituents. Nectar sugars from flowers visited by hummingbirds average 76.2% sucrose and have compositions remarkably similar to hummingbird nectars analyzed in previous studies of unrelated species. Long-tongued bee nectars average 87% sucrose and differ from shorttongued bee nectars which have the lowest mean sucrose percentage (40.2%). The association of sugar constituent types and principal pollinators is concordant with previous data and supports hypotheses concerning pollinator preferences and the adaptive significance of certain nectar sugar compositions. Within this adaptive framework, phylogenetic constraint is also operative and may explain the predominance of sucrose in nectar sugars, similarities in sugar composition among hummingbird nectars in subtribes Maurandyinae and Gambeliinae, and the similarity of nectar from Galvezia leucantha (long-tongued bee-pollinated) to hummingbird-pollinated species also in subtribe Gambeliinae.     

Variation in floral morphology and plant reproductive success in four Ipomoea species (Convolvulaceae) with contrasting breeding systems

• This study tested the hypothesis that self‐compatibility would be associated with floral traits that facilitate autonomous self‐pollination to ensure reproduction under low pollinator visitation. In a comparison of two pairs of Ipomoea species with contrasting breeding systems, we predicted that self‐compatible (SC) species would have smaller, less variable flowers, reduced herkogamy, lower pollinator visitation and higher reproductive success than their self‐incompatible (SI) congeners.
• We studied sympatric species pairs, I. hederacea (SC)– I. mitchellae (SI) and I. purpurea (SC)–I. indica (SI), in Mexico, over two years. We quantified variation in floral traits and nectar production, documented pollinator visitation, and determined natural fruit and seed set. Hand‐pollination and bagging experiments were conducted to determine potential for autonomous self‐pollination and apomixis.
• Self‐compatible Ipomoea species had smaller flowers and lower nectar production than SI species; however, floral variation and integration did not vary according to breeding system. Bees were primary pollinators of all species, but visitation rates were seven times lower in SC than SI species. SC species had a high capacity for autonomous self‐pollination due to reduced herkogamy at the highest anther levels. Self‐compatible species had two to six times higher fruit set than SI species.
• Results generally support the hypothesis that self‐compatibility and autonomous self‐pollination ensure reproduction under low pollinator visitation. However, high variation in morphological traits of SC Ipomoea species suggests they maintain variation through outcrossing. Furthermore, reduced herkogamy was associated with high potential for autonomous self‐pollination, providing a reproductive advantage that possibly underlies transitions to self‐compatibility in Ipomoea.

     

Nectar Sugar Production across Floral Phases in the Gynodioecious Protandrous Plant Geranium sylvaticum

Many zoophilous plants attract their pollinators by offering nectar as a reward. In gynodioecious plants (i.e. populations are composed of female and hermaphrodite individuals) nectar production has been repeatedly reported to be larger in hermaphrodite compared to female flowers even though nectar production across the different floral phases in dichogamous plants (i.e. plants with time separation of pollen dispersal and stigma receptivity) has rarely been examined. In this study, sugar production in nectar standing crop and secretion rate were investigated in Geranium sylvaticum, a gynodioecious plant species with protandry (i.e. with hermaphrodite flowers releasing their pollen before the stigma is receptive). We found that flowers from hermaphrodites produced more nectar than female flowers in terms of total nectar sugar content. In addition, differences in nectar production among floral phases were found in hermaphrodite flowers but not in female flowers. In hermaphrodite flowers, maximum sugar content coincided with pollen presentation and declined slightly towards the female phase, indicating nectar reabsorption, whereas in female flowers sugar content did not differ between the floral phases. These differences in floral reward are discussed in relation to visitation patterns by pollinators and seed production in this species.     

Phenotypic selection on nectar amino acid composition in the Lepidoptera pollinated orchid species Gymnadenia conopsea

Plant–pollinator interactions are potential drivers of evolution in floral traits. Because nectar chemical composition is known to mediate both plant–pollinator interactions and plant reproductive success, it can be expected that chemical composition of nectar is subjected to strong pollinator‐mediated selective forces. However, the extent of natural selection on different nectar components has not been studied so far. Using the Lepidoptera pollinated fragrant orchid Gymnadenia conopsea as a model species, we used high‐performance anion‐exchange chromatography (HPAEC) to characterize the sugar and amino acid composition of floral nectar in three calcareous grassland populations of G. conopsea. We then measured phenotypic selection on nectar composition and on other plant and floral traits through applying both linear regression and structural equation modelling. We demonstrate phenotypic selection on plant height, inflorescence height and on specific nectar amino acids, whereas spur length, total sugar and amino acid concentration were not direct targets of selection. Chemical nectar composition is thus indeed under selective pressure but nectar amino acids are much more important to fitness of G. conopsea, as compared to nectar sugars. Furthermore, as we found no evidence of selection on the total amino acid concentration, it is unlikely that amino acids increase pollinator attraction because they are a pollinator nitrogen source. To further unravel the evolutionary ecology of floral nectar, behavioural experiments with pollinators exposed to different nectar components and studies experimentally identifying the selective agents are recommended.     

Pollinators and nectar robbers cause directional selection for large spur circle in Impatiens oxyanthera (Balsaminaceae)

Nectar spurs have an important role in floral evolution and plant–pollinator coadaptation. The flowers of some species possess spurs curving into a circle. However, it is unclear whether spur circle diameter is under direct selection pressure from different sources, such as pollinators and nectar robbers. In this study, we quantified selection on some floral traits, such as spur circle diameter in Impatiens oxyanthera (Balsaminaceae) using phenotypic selection analysis and compared the relative importance of pollinators and nectar robbers as selective agents using mediation analysis. The study showed that pollinators caused significant selection on corolla length, spur curvature and spur circle diameter while nectar robbers only imposed strong selection on spur circle diameter. Pollinators favored flowers with large corolla, curly spurs and large spur circle while nectar robbers preferred flowers with small spur circle. More pollinator visits resulted in higher female reproductive success, while robbery reduced female fitness. Conflicting selection on spur traits from pollinators and nectar robbers was not found. Mediation analysis showed that selection on floral traits through nectar robbing was stronger than selection through pollination. The results suggested that pollinators and nectar robbers jointly mediated the directional selection for large spur circle, and nectar robbers caused stronger selection than pollinators on floral traits.     

Drought reduces floral resources for pollinators

Climate change is predicted to result in increased occurrence and intensity of drought in many regions worldwide. By increasing plant physiological stress, drought is likely to affect the floral resources (flowers, nectar and pollen) that are available to pollinators. However, little is known about impacts of drought at the community level, nor whether plant community functional composition influences these impacts. To address these knowledge gaps, we investigated the impacts of drought on floral resources in calcareous grassland. Drought was simulated using rain shelters and the impacts were explored at multiple scales and on four different experimental plant communities varying in functional trait composition. First, we investigated the effects of drought on nectar production of three common wildflower species (Lathyrus pratensis, Onobrychis viciifolia and Prunella vulgaris). In the drought treatment, L. pratensis and P. vulgaris had a lower proportion of flowers containing nectar and O. viciifolia had fewer flowers per raceme. Second, we measured the effects of drought on the diversity and abundance of floral resources across plant communities. Drought reduced the abundance of floral units for all plant communities, irrespective of functional composition, and reduced floral species richness for two of the communities. Functional diversity did not confer greater resistance to drought in terms of maintaining floral resources, probably because the effects of drought were ubiquitous across component plant communities. The findings indicate that drought has a substantial impact on the availability of floral resources in calcareous grassland, which will have consequences for pollinator behaviour and populations.     

The relative strength of different floral visitors driving floral evolution within a <Emphasis Type="Italic">Primula secundiflora</Emphasis> population

Floral visitor assemblages within plant populations are usually composed of different visitors, and the relative abundance of these visitors also varies. Therefore, identifying the relative strength of these floral visitors driving floral evolution within the population is an important step in predicting the evolutionary trajectory of floral traits. Using supplemental hand pollination and nectar-robbing exclusion treatments, we experimentally identified the relative strengths of legitimate pollinators (that visit flowers through the corolla tube entrance) and nectar robbers (that visit flowers by biting a hole in the corolla tube or using an existing hole) driving floral evolution within the Primula secundiflora population. We also estimated legitimate pollinator- and nectar robber-mediated selection separately for pin and thrum flowers. Both legitimate pollinators and nectar robbers mediated selection on pollination efficiency traits in P. secundiflora population. Legitimate pollinators mediated selection for wider corolla tubes, whereas nectar robbers mediated selection for longer corolla tubes. In addition, nectar robber-mediated selection on corolla tube length marginally varied between the pin and thrum flowers. Nectar robber mediated selection for longer corolla tube length in the pin flowers not in the thrum flowers. These results indicate that legitimate pollinators and nectar robbers within a population can drive differential evolutionary trajectories of floral traits.     

Main sugar composition of floral nectar in three species groups of Scrophularia (Scrophulariaceae) with different principal pollinators

In some angiosperm groups, a parallelism between nectar traits and pollination syndromes has been demonstrated, whereas in others there is not such relationship and it has been explained as due to phylogenetic constraints. However, nectar trait information remains scarce for many plant groups. This paper focuses on three groups of Scrophularia species, with different flower sizes and principal pollinators, to find out whether nectar sugar composition is determined by pollinator type or reflects taxonomic affinities. Since the species we examined have protogynous flowers, and gender bias in nectar sugar composition has been noted in few plant groups, we also investigated whether sexual phase influenced Scrophularia nectar composition. The sugar composition was found to be similar in all species, having high‐sucrose nectar, except for the Macaronesian Scrophularia calliantha, which was the only species with balanced nectar; this last kind of nectar could be associated with the high interaction rates observed between S. calliantha and passerine birds. The nectar sugar composition (high in sucrose) was unrelated to the principal pollinator group, and could instead be considered a conservative taxonomic trait. No gender bias was observed between functionally female and male flowers for nectar volume or concentration. However, sexual phase significantly affected sucrose percentage in the largest‐flowered species, where the female phase flowers had higher sucrose percentages than the male phase flowers.     

Nectar robbers influence the trait–fitness relationship of Primula secundiflora

• The trait–fitness relationship influences the strength and direction of floral evolution. To fully understand and predict the evolutionary trajectories of floral traits, it is critical to disentangle the direct and indirect effects of floral traits on plant fitness in natural populations.
• We experimentally quantified phenotypic selection on floral traits through female fitness and estimated the casual effects of nectar robbing with different nectar robbing intensities on trait–fitness relationships in both the L‐ (long‐style and short‐anther phenotype) and S‐morph (short‐style and long‐anther phenotype) flowers among Primula secundiflora populations.
• A larger number of flowers and wider corolla tubes had both direct and indirect positive effects on female fitness in the P. secundiflora populations. The indirect effects of these two traits on female fitness were mediated by nectar robbers. The indirect effect of the number of flowers on female fitness increased with increasing nectar robbing intensity. In most populations, the direct and/or indirect effects of floral traits on female fitness were stronger in the S‐morph flowers than in the L‐morph flowers. In addition, nectar robbers had a direct positive effect on female fitness, but this effect varied between the L‐ and S‐morph flowers.
• These results show the potential role of nectar robbers in influencing the trait–fitness relationships in this primrose species.

     

Pollination biology of the hexaploid self‐compatible species Turnera velutina (Passifloraceae)

• The evolution of monomorphisms from heterostylous ancestors has been related to the presence of homostyly and the loss of self‐incompatibility, allowing the occurrence of selfing, which could be advantageous under pollinator limitation. However, flowers of some monomorphic species show herkogamy, attraction and rewarding traits that presumably favour cross‐pollination and/or a mixed mating system. This study evaluated the contributions of pollinators, breeding system and floral traits to the reproduction of Turnera velutina, a herkogamous monomorphic species.
• Floral visitors and frequency of visits were recorded, controlled hand cross‐pollinations were conducted under greenhouse and natural conditions, and individual variation in floral traits was characterised to determine their contribution to seed production.
• Apis mellifera was the most frequent floral visitor. Flowers presented approach herkogamy, high variation in nectar features, and a positive correlation of floral length with nectar volume and sugar concentration. Seed production did not differ between manual self‐ and cross‐pollinations, controls or open cross‐pollinations, but autonomous self‐pollination produced, on average, 82.74% fewer seeds than the other forms, irrespective of the level of herkogamy.
• Differences in seed production among autonomous self‐pollination and other treatments showed that T. velutina flowers depend on insect pollination for reproduction, and that approach herkogamy drastically reduced seed production in the absence of pollen vectors. The lack of differences in seed production from manual cross‐ and self‐pollinations suggests the possible presence of a mixed mating system in the studied population. Overall, this species was possibly derived from a distylous ancestor but appears fully capable of outcrossing despite being monomorphic.