Pollination in Lilium sargentiae (Liliaceae) and the first confirmation of long‐tongued hawkmoths as a pollinator niche in Asia

The geographical distribution of pollinators is an important factor determining the biogeographical pattern of floral evolution and diversification. In Africa, a guild of plant species has converged in a floral syndrome for pollination by long‐tongued hawkmoths (predominantly Agrius convolvuli). It is hypothesized that such floral convergence could track the geographical distribution of long‐tongued hawkmoths, so it may not be confined to Africa. We investigated the pollination biology of Lilium sargentiae E. H. Wilson, which is endemic to China and exhibits traits suggestive of long‐tongued hawkmoth pollination. Lilium sargentiae was visited by A. convolvuli as well as small beetles (Nitidulidae) but pollination was mostly or totally effected by the moth. It was consistent with other hawkmoth‐pollinated plants in terms of floral tube length, nectar traits, tepal reflectance, and scent composition. We present the first experimental evidence for the hypothesis proposed above and for hawkmoth pollination in the widespread and ornamentally and economically important genus Lilium L. in a natural habitat. Our findings imply that long‐tongued hawkmoths (especially the extremely widespread A. convolvuli) as a distinctive pollinator niche may have underlain the evolution of long‐tubed (>8 cm) flowers across different continents.     

A one‐locus model of androdioecy with two homomorphic self‐incompatibility groups: expected vs. observed male frequencies

Androdioecy, the occurrence of males and hermaphrodites in a single population, is a rare breeding system because the conditions for maintenance of males are restrictive. In the androdioecious shrub Phillyrea angustifolia, high male frequencies are observed in some populations. The species has a sporophytic self‐incompatibility (SI) system with two self‐incompatibility groups, which ensures that two groups of hermaphrodites can each mate only with the other group, whereas males can fertilize hermaphrodites of both groups. Here, we analyse a population genetic model to investigate the dynamics of such an androdioecious species, assuming that self‐incompatibility and sex phenotypes are determined by a single locus. Our model confirms a previous prediction that a slight reproductive advantage of males relative to hermaphrodites allows the maintenance of males at high equilibrium frequencies. The model predicts different equilibria between hermaphrodites of the two SI groups and males, depending on the male advantage, the initial composition of the population and the population size, whose effect is studied through stochastic simulations. Although the model can generate high male frequencies, observed frequencies are considerably higher than the model predicts. We finally discuss how this model may help explain the large male frequency variation observed in other androdioecious species of Oleaceae: some species show only androdioecious populations, as P. angustifolia, whereas others show populations either completely hermaphrodite or androdioecious.     

Effects of pollen availability and the mutation bias on the fixation of mutations disabling the male specificity of self‐incompatibility

The evolution of self‐compatibility (SC) by the loss of self‐incompatibility (SI) is regarded as one of the most frequent transitions in flowering plants. SI systems are generally characterized by specific interactions between the male and female specificity genes encoded at the S‐locus. Recent empirical studies have revealed that the evolution of SC is often driven by male SC‐conferring mutations at the S‐locus rather than by female mutations. In this study, using a forward simulation model, we compared the fixation probabilities of male vs. female SC‐conferring mutations at the S‐locus. We explicitly considered the effects of pollen availability in the population and bias in the occurrence of SC‐conferring mutations on the male and female specificity genes. We found that male SC‐conferring mutations were indeed more likely to be fixed than were female SC‐conferring mutations in a wide range of parameters. This pattern was particularly strong when pollen availability was relatively high. Under such a condition, even if the occurrence of mutations was biased strongly towards the female specificity gene, male SC‐conferring mutations were much more often fixed. Our study demonstrates that fixation probabilities of those two types of mutation vary strongly depending on ecological and genetic conditions, although both types result in the same evolutionary consequence—the loss of SI.     

Flower preferences and pollen transport networks for cavity‐nesting solitary bees: Implications for the design of agri‐environment schemes

Floral foraging resources are valuable for pollinator conservation on farmland, and their provision is encouraged by agri‐environment schemes in many countries. Across Europe, wildflower seed mixtures are widely sown on farmland to encourage pollinators, but the extent to which key pollinator groups such as solitary bees exploit and benefit from these resources is unclear. We used high‐throughput sequencing of 164 pollen samples extracted from the brood cells of six common cavity‐nesting solitary bee species (Osmia bicornis, Osmia caerulescens, Megachile versicolor, Megachile ligniseca, Megachile centuncularis and Hylaeus confusus) which are widely distributed across the UK and Europe. We documented their pollen use across 19 farms in southern England, UK, revealing their forage plants and examining the structure of their pollen transport networks. Of the 32 plant species included currently in sown wildflower mixes, 15 were recorded as present within close foraging range of the bees on the study farms, but only Ranunculus acris L. was identified within the pollen samples. Rosa canina L. was the most commonly found of the 23 plant species identified in the pollen samples, suggesting that, in addition to providing a nesting resource for Megachile leafcutter bees, it may be an important forage plant for these species. Higher levels of connectance and nestedness were characteristic of pollen transport networks on farms with abundant floral resources, which may increase resilience to species loss. Our data suggest that plant species promoted currently by agri‐environment schemes are not optimal for solitary bee foraging. If a diverse community of pollinators is to be supported on UK and European farmland, additional species such as R. canina should be encouraged to meet the foraging requirements of solitary bees.     

Adaptations for nectar‐feeding in the mouthparts of long‐proboscid flies (Nemestrinidae: Prosoeca)

The insects with the longest proboscis in relation to body length are the nectar‐feeding Nemestrinidae. These flies represent important pollinators of the South African flora and feature adaptations to particularly long‐tubed flowers. The present study examined the morphology of the extremely long and slender mouthparts of Nemestrinidae for the first time. The heavily sclerotized tubular proboscis of flies from the genus Prosoeca is highly variable in length. It measures 20–47 mm in length and may exceed double the body length in some individuals. Proximally, the proboscis consists of the labrum–epipharynx unit, the laciniae, the hypopharynx, and the labium. The distal half is composed of the prementum of the labium, which solely forms the food tube. In adaptation to long‐tubed and narrow flowers, the prementum is extremely elongated, bearing the short apical labella that appear only to be able to spread apart slightly during nectar uptake. Moving the proboscis from resting position under the body to a vertical feeding position is accomplished in particular by the movements of the laciniae, which function as a lever arm. Comparisons with the mouthparts of other flower visiting flies provide insights into adaptations to nectar‐feeding from long‐tubed flowers. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Self‐ and intra‐morph incompatibility and selection analysis of an inconspicuous distylous herb growing on the Tibetan plateau (Primula tibetica)

There is discussion over whether pollen limitation exerts selection on floral traits to increase floral display or selects for traits that promote autonomous self‐fertilization. Some studies have indicated that pollen limitation does not mediate selection on traits associated with either pollinator attraction or self‐fertilization. Primula tibetica is an inconspicuous cross‐fertilized plant that may suffer from pollen limitation. We conducted a selection analysis on P. tibetica to investigate whether pollen limitation results in selection for an increased floral display in case the evolution of autonomous self‐fertilization has been difficult for this plant. The self‐ and intra‐morph incompatibility features, the capacity for autonomous self‐fertilization, and the magnitude of pollen limitation were examined through hand‐pollination experiments. In 2016, we applied selection analysis on the flowering time, corolla width, stalk height, flower tube length, and flower number in P. tibetica by tagging 76 open‐pollinated plants and 37 hand‐pollinated plants in the field. Our results demonstrated that P. tibetica was strictly self‐ and intra‐morph incompatible. Moreover, the study population underwent severe pollen limitation during the 2016 flowering season. The selection gradients were found to be significantly positive for flowering time, flower number, and corolla width, and marginally significant for the stalk height. Pollinator‐mediated selection was found to be significant on the flower number and corolla width, and marginally significant on stalk height. Our results indicate that the increased floral display may be a vital strategy for small distylous species that have faced difficulty in evolving autonomous self‐fertilization.     

Flower visitation patterns of the coexisting honey bees Apis cerana japonica and Apis mellifera (Hymenoptera: Apidae)

We compared flower visitation patterns of two coexisting honey bees, Apis mellifera Linnaeus and Apis cerana japonica Radoszkowski, on 20 plant species, including three exotics, under natural conditions in Nara, Japan, from April to August 2012. We also measured flower color based on bee color vision (15 flower species), nectar volume (nine species) and nectar concentration (eight species). Flowers colored white, pink, red, purple and cream were classified as bee‐blue‐green, and yellow was classified as bee‐green. Apis cerana visited 14 plant species and A. mellifera visited 11. Although the two Apis species are similar in morphology, they visited different plants: in particular, A. cerana visited native plant species more often than did A. mellifera. Both A. mellifera and A. cerana visited not only nectariferous flowers but also those with no nectar. We also found different visitation patterns between A. cerana and A. mellifera: Apis cerana more often visited flowers with smaller color angle (bee‐blue‐green), lower chroma and higher brightness, and flowers secreting nectars of higher concentration and smaller volume than did A. mellifera.     

Breakdown of distyly and pin‐monomorphism in Psychotria carthagenensis Jacq. (Rubiaceae)

Rubiaceae contains the largest number of distylous species in the Angiosperms, but the evolution and control of distyly is poorly understood in this group. Atypical distylous populations and species have been described in this family and associated with disturbance, pollination failure and impaired reproductive success. Some of these atypical taxa belong to Psychotria, the largest genus in the family. In the present study, we investigate the pollination and breeding biology of Psychotria carthagenensis Jacq., a widely distributed species that has been described as typically distylous. Fieldwork was carried out mainly at the Panga Ecological Station, in Uberlândia, MG, Brazil. We carried out phenological observations, floral biology studies and hand pollination experiments within the Panga Ecological Station population. We complemented these data with herbarium and field surveys from elsewhere in Brazil. The studied population bloomed at the beginning of the rains (September–December). The main pollinators were Bombus and small Halictidae bees. The Panga Ecological Station population presented pin‐monomorphism with only two thrum individuals in more than 100 flowering individuals surveyed. Hand pollinations at the Panga Ecological Station showed self‐compatibility and intramorph compatibility. Typical distyly and isoplethy were found in other areas and both morphs appeared in herbarium material. However, pin‐monomorphism was also observed elsewhere in Brazil. Typical distyly, pin‐monomorphism and homostyly observed concurrently in Brazilian populations of P. carthagenensis indicate that alternative reproductive strategies, probably favoring selfing, appear to have developed independently in this 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.

     

Do introduced honeybees (Apis mellifera,Hymenoptera) provide full pollination service to bird‐adapted Australian plants with small flowers? An experimental study of Brachyloma ericoides (Epacridaceae)

Abstract In many previous studies of the effects of introduced honeybees on Australian ecosystems, it has been assumed that floral morphology is a primary factor determining whether introduced honeybees will be effective in pollinating endemic plants. Although both honeybees and birds contacted stigmas and anthers of the small‐flowered Brachyloma ericoides (Epacridaceae), the exclusion of birds but not honeybees resulted in a significantly lower proportion of flowers producing capsules (12.3 ± 2 vs 21.0 ± 2%). This suggests that native birds contributed significantly to fruit set even though honeybees were much more frequent visitors to flowers (5–6 vs 0.7–2.5 times per day) and moved more frequently between plants (25 vs 12.2% of movements). Fruit set following exposure to birds and honeybees was very low compared with shrub species in general and may have been limited by the pre‐emptive removal of pollen by the 10% of honeybees that actively collected pollen.     

The effectiveness of pre‐ and post‐zygotic barriers in avoiding hybridization between two snapdragons (Antirrhinum L.: Plantaginaceae)

Reproductive barriers play an important role in the maintenance of species boundaries. However, to date, few studies have provided a detailed analysis of reproductive isolation barriers between species or examined their importance in maintaining species identity. This is the first detailed study into pre‐ and post‐zygotic reproductive isolation barriers in Antirrhinum, based on a mixed population with two species that rarely co‐occur. The study revealed that pollinator constancy and preference and poor hybrid seed viability were the most important reproductive isolating mechanisms. Reproductive isolation was practically complete by both pre‐ and post‐zygotic barriers. Average pre‐zygotic isolation was greater than post‐zygotic isolation, in accordance with the trend observed in flowering plants in which reproductive isolation is principally caused by pre‐zygotic mechanisms. However, average post‐zygotic isolation was also high, in contrast to what was expected among Antirrhinum spp. This case highlights the importance of quantifying the reproductive isolation barriers thoroughly to understand how and why species boundaries are maintained. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176 , 159–172.     

Pollination of Campomanesia phaea (Myrtaceae) by night‐active bees: a new nocturnal pollination system mediated by floral scent

• Bees are the most important diurnal pollinators of angiosperms. In several groups of bees a nocturnal/crepuscular habit developed, yet little is known about their role in pollination and whether some plants are adapted specifically to these bees. We used a multidisciplinary approach to investigate the reproductive biology and to understand the role of nocturnal/crepuscular bees in pollination of Campomanesia phaea (Myrtaceae), popularly named cambuci.
• We studied the floral biology and breeding system of C. phaea. We collected the floral visitors and tested the pollinators' effectiveness. We also determined the floral scents released at night and during daytime, and studied behavioural responses of crepuscular/nocturnal bees towards these scents.
• The flowers of cambuci were self‐incompatible and had pollen as the only resource for flower visitors. Anthesis lasted around 14 h, beginning at 04:30 h at night. The flowers released 14 volatile compounds, mainly aliphatic and aromatic compounds. We collected 52 species of floral visitors, mainly bees. Nocturnal and crepuscular bees (four species) were among the most frequent species and the only effective pollinators. In field bioassays performed at night, nocturnal/crepuscular bees were attracted by a synthetic scent blend consisting of the six most abundant compounds.
• This study describes the first scent‐mediated pollination system between a plant and its nocturnal bee pollinators. Further, C. phaea has several floral traits that do not allow classification into other nocturnal pollination syndromes (e.g. pollinator attraction already before sunrise, with pollen as the only reward), instead it is a plant specifically adapted to nocturnal bees.

     

Perfume-collecting male euglossine bees as pollinators of a basal angiosperm: the case of Unonopsis stipitata (Annonaceae)

Pollination of Unonopsis stipitata (Annonaceae) by males of two perfume-collecting bees, Euglossa imperialis and Eulaema bombiformis (Euglossini) is described. This is the first detailed account of this pollination mode in a member of a basal angiosperm family. Pollinator behaviour, identification of the odour bouquet and electrophysiological reaction of one of the two pollinators to the odour bouquet were determined. The collected odour is produced by 'osmophores' located adaxially on the petals. Starch and polysaccharides accumulated in petals are metabolized during odour emission. Mainly monoterpenes were detected in the scent samples, among them trans-carvone oxide. This molecule is thought by several authors to be the key attractant for male Eulaema bees and may be pivotal for convergent evolution of the perfume-collecting syndrome among dicotyledonous and monocotyledonous plants. It is speculated that Unonopsis , which on the basis of molecular age dating is considered a relatively recent genus of the Annonaceae (being 15–30 million years old), has diversified in relation to male euglossine bee pollinators.     

Neighbouring‐group composition and within‐group relatedness drive extra‐group paternity rate in the European badger (Meles meles)

Extra‐group paternity (EGP) occurs commonly among group‐living mammals and plays an important role in mating systems and the dynamics of sexual selection; however, socio‐ecological and genetic correlates of EGP have been underexplored. We use 23 years of demographic and genetic data from a high‐density European badger (Meles meles) population, to investigate the relationship between the rate of EGP in litters and mate availability, mate incompatibility and mate quality (heterozygosity). Relatedness between within‐group assigned mothers and candidate fathers had a negative quadratic effect on EGP, whereas the number of neighbouring‐group candidate fathers had a linear positive effect. We detected no effect of mean or maximum heterozygosity of within‐group candidate fathers on EGP. Consequently, EGP was associated primarily with mate availability, subject to within‐group genetic effects, potentially to mitigate mate incompatibility and inbreeding. In badgers, cryptic female choice, facilitated by superfecundation, superfoetation and delayed implantation, prevents males from monopolizing within‐group females. This resonates with a meta‐analysis in group‐living mammals, which proposed that higher rates of EGP occur when within‐group males cannot monopolize within‐group females. In contrast to the positive meta‐analytic association, however, we found that EGP associated negatively with the number of within‐group assigned mothers and the number of within‐group candidate fathers; potentially a strategy to counter within‐group males committing infanticide. The relationship between the rate of EGP and socio‐ecological or genetic factors can therefore be intricate, and the potential for cryptic female choice must be accounted for in comparative studies.     

The bees don't know and the flowers don't care: the effect of heterospecific pollen on reproduction in co‐occurring Thysanotus species (Asparagaceae) with similar flowers

Species integrity relies on the maintenance of reproductive isolation, particularly between closely related species. Further, it has been hypothesized that the presence of heterospecific pollen on flower stigmas adversely affects plant reproduction with increasing effect in closely related species. Using two pairs of co‐occurring buzz‐pollinated Thysanotus spp. in the Mediterranean climate region of Perth, Western Australia, we quantified the effect of heterospecific pollen on fruit and seed set. We first determined the mating systems of the two focal species using self‐ and outcross pollen, followed by separate treatments with heterospecific pollen within each species pair. Of the two species receiving pollen, Thysanotus triandrus had a mixed mating system, but with significantly lower fruit and seed set from self‐pollen relative to outcross pollen. Thysanotus tenellus was autogamous with no difference in fruit or seed set between autogamous, self‐ or outcross pollinations. Heterospecific pollen had no effect on fruit or seed set of either focal species. These outcomes point to post‐pollination reproductive isolation, consistent with a floral morphology that causes low specificity of pollen placement and thus a poor capacity for pre‐pollination discrimination. Negative effects of heterospecific pollen, therefore, do not appear to play a role in the reproduction in this group of buzz‐pollinated flowers.     

Description of a new species of the genus Resseliella (Diptera: Cecidomyiidae), a pollinator of Kadsura longipedunculata (Schisandraceae) in China,with comments on its flower‐visiting habit

A gall midge pollinating flowers of Kadsura longipedunculata is described as Resseliella kadsurae sp. nov. based on adult specimens collected in 2006 from Langshan, Xinning County, Hunan Province, China. The new species is distinguishable from other known congeners in the combination of the following characteristics: gynecoid male flagellomeres, mottled wings, simple claws on all legs; male hypoproct with a transverse bridge‐like structure ventrally connecting both sides of hypoproct. In particular, the gynecoid male flagellomeres and transverse bridge‐like structure are unique to the new species. Partial sequencing of the cytochrome oxidase subunit I mitochondrial gene indicates that R. kadsurae is grouped with the R. theobardi + R. yagoi clade, but this clade and the monophyly of the genus Resseliella are not statistically supported. The new species is nocturnal, and mating occurs at dusk. At the time of mating, males and females hang on opposite sides of non‐sticky old spider webs in a venter‐to‐venter position. Immature stages and the life history of R. kadsurae are unknown. The flower‐visiting habit of R. kadsurae is contrasted with that of other flower‐visiting gall midges and the probability that this behavior exists in other congeners is discussed.     

Mixed colonies of two species of congeneric stingless bees (Hymenoptera: Apinae,Meliponini) display environmentally‐acquired and endogenously‐produced recognition signals

Nestmate recognition is fundamental for the maintenance of social organization in insect nests. It is becoming well recognized that cuticle hydrocarbons mediate the recognition process, although the origin of recognition cues in stingless bees remains poorly explored. The present study investigates the effects of endogenously‐produced and environmentally‐acquired components in cuticular hydrocarbons in stingless bees. The tests are conducted using colonies of Plebeia droryana Friese and Plebeia remota Holmberg. Recognition tests are performed with four different groups: conspecific nestmates, conspecific non‐nestmates, heterospecifics and conspecific, genetically‐related individuals that emerge in a heterospecific nest. This last group is produced by introducing brood cells of P. droryana into a P. remota colony, and the resulting adult bees are tested for acceptance 10 days after emergence. For all groups, 15 individuals are sampled for chemical analysis. The results show the acceptance of all conspecific nestmates, and the rejection of almost every conspecific non‐nestmate and every heterospecific bee. Genetically‐related individuals emerging from heterospecific nests present intermediate rejection (66.7% rejection). Chemical analysis shows that P. droryana individuals emerging in a P. remota nest have small amounts of alkene and diene isomers found in P. remota cuticle that are not found in workers from the natal nest. The data clearly show that the majority of the compounds present in P. droryana cuticle are endogenously produced, although a few unsaturated compounds are acquired from the environment, increasing the chemical differences and, consequently, the rejection percentages.