Flowering patterns of long-lived Heliconia inflorescences: implications for visiting and resident nectarivores

Summary Flowering patterns of four Heliconia (Heliconiaceae) species in Trinidad, West Indies were examined for their predictability and availability to the nectarivores that rely on Heliconia floral nectar. Principal flower visitors are trapling hermit hummingbirds; inflorescences are inhabited by nectarivorous hummingbird flower mites that move between inflorescences by riding in the hummingbirds' nares. Heliconia inflorescences flower for 40–200 days, providing long-term sources of copious nectar (30–60 l per flower), but each Heliconia flower lasts only a single day. As an inflorescence ages the interval increases between open flowers within a bract; wet-season inflorescences produce open flowers more slowly than dry-season conspecifics.Estimated daily energy expenditures for hermit hummingbirds demonstrate that slow production of short-lived open flowers plus low inflorescence density preclude territorial defense of Heliconia by the hermits. Heliconia flowering patterns are viewed as a means of (i) regulating reproductive investment by the plants through staggered flower production over long periods of time, and (ii) maintaining outcrossing by necessitating a traplining visitation pattern by its hummingbird pollinators. I suggest that Heliconia exhibit a two-tiered pollination system by using hermit hummingbirds primarily for outcrossing and using hummingbird flower mites primarily for self-pollination.     

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.     

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

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

     

A Geographic Mosaic of Plant–Pollinator Interactions in the Eastern Caribbean Islands

The interplay between generalized and specialized plant–animal interactions is a core concept in understanding the evolution of mutualisms. Within the Eastern Caribbean, Heliconia bihai is a dominant forest species in the southern island of St. Vincent where H. caribaea is virtually absent. Heliconia caribaea is most common on the northern island of St. Kitts where H. bihai is restricted to the tops of the highest peaks. Both species are abundant on the central island of Dominica. We compared flowering patterns, nectar characteristics, and visitation frequency of hummingbirds in the two heliconias on the three islands to determine the extent of geographic variations in this plant–pollinator mutualism. The peak flowering season of the two heliconias was observed to be in April–May on all three islands with little within‐ and between‐island variations. Nectar production significantly varied between species and between islands. Visitation patterns by the principal hummingbird pollinators also varied between the islands: (1) on Dominica, only females of a single species of hummingbird pollinated the flowers of H. bihai (sexual specialization), whereas both sexes of the same hummingbird pollinated the flowers of H. caribaea (species specialization); (2) on St. Vincent, both sexes of the same hummingbird pollinated the flowers of H. bihai (species specialization); and (3) on St. Kitts, only females pollinated the flowers of H. bihai (sexual specialization), whereas several species of hummingbird visited the flowers of H. caribaea (species generalization). We propose that the Heliconia–hummingbird interactions in the Eastern Caribbean represent a geographically variable coevolutionary mosaic of plant–pollinator interactions.     

Different rewards in female and male flowers can explain the evolution of sexual dimorphism in plants

Insects use floral signals to find rewards in flowers, transferring pollen in the process. In unisexual plants, the general view is that staminate (male) and pistillate (female) flowers obtain conspecific pollen transfers by advertising their rewards with similar floral signals. For female plants lacking food rewards, this can lead to floral mimicry and pollination by deceit. In this study, we challenge this view by presenting evidence for different rewards offered by flowers on females and males, as a mechanism promoting sexual dimorphism in Leucadendron xanthoconus (Proteaceae), a clearly sexually dimorphic shrub. The tiny beetle pollinators Pria cinerascens (Nitidulidae) depend entirely on the plants they pollinate for survival and reproduction. Male flowers provide mating and egglaying sites, and food for adults and larvae. Female flowers lack nectar and function to shelter pollinators from rain. Their flower heads have cup‐shaped display leaves, and are more closed than are those in males. On rainy days, flowers on females received 30% more visits than did flowers on males, and 90% more than they did on sunny days. When we removed display leaves in females, intact flower heads received 14 times more P. cinerascens visits than did manipulated flower heads, indicating that the cup shape attracts the beetles. In both sexes, having many flowers increased the probability of visits and the number of P. cinerascens visiting a plant. In males, the number of larvae was positively correlated with floral‐display size, while in females, seed set (pollen transfers) showed no relationship with floral‐display size. Ninety‐five per cent of the ovules received pollen and 52% matured into seeds. We explain the sexual dimorphism in L. xanthoconus as a result of an intimate partnership with P. cinerascens pollinators, in conjunction with a rainy climate. Pollinators favour large male floral displays, because they offer a reliable food source for adults and larvae. Frequent rains drive the P. cinerascens to leave males in search of the protection offered by females. Because females offer shelter, an essential resource that is not offered by male plants, they receive sufficient pollen independent of their floral‐display size. This pollination system promotes the evolution of sexually dimorphic floral signals, guiding pollinators to different rewards in male and female flowers. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85 , 97–109.     

The potential significance of nectar‐feeding bats as pollinators in mangrove habitats of Peninsular Malaysia

We tested the hypothesis that bats are effective pollinators of mangroves in Malaysia. Bats (Eonycteris spelaea) visited flowers of two Sonneratia species frequently, and deposited large quantities of conspecific pollen grains on stigmas. The bats are likely to be important pollinators of the two mangrove species.     

Reproductive biology and pollination of the carnivorous Genlisea violacea (Lentibulariaceae)

• Genlisea violacea is a Brazilian endemic carnivorous plant species distributed in the cerrado biome, mainly in humid environments, on sandy and oligotrophic soil or wet rocks. Studies on reproductive biology or pollination in the Lentibulariaceae are notably scarce; regarding the genus Genlisea, the current study is the first to show systematic and standardised research on reproductive biology from field studies to describe the foraging of visiting insects and determine the effective pollinators of Genlisea.
• We studied two populations of G. violacea through the observation of flower visitors for 4 months of the rainy and dry seasons. Stigmatic receptivity, pollen viability, and breeding system were evaluated together with histochemistry and morphological analyses of flowers.
• The flowers showed stigmatic receptivity of 100% in open buds and mature flowers, reducing to 80% for senescent flowers. Nearly 80% of pollen grains are viable, decreasing to 40–45% after 48 h. Nectar is produced by glandular trichomes inside the spur. Two bee species are effective pollinators: one of the genus Lasioglossum (subgenus Dialictus: Halictidae) and the other of the genus Ceratina (subgenus Ceratinula: family Apidae). Moreover, bee‐like flies of the Syrphidae family may also be additional pollinators.
• Genlisea violacea is an allogamous and self‐compatible species. The differences in flower‐visiting fauna for both populations can be attributed to factors such as climate, anthropogenic effect, seasonal factors related to insects and plants, as well as the morphological variation of flowers in both populations.

     

Pollen transfer in fragmented plant populations: insight from the pollen loads of pollinators and stigmas in a mass‐flowering species

Pollinator and/or mate scarcity affects pollen transfer, with important ecological and evolutionary consequences for plant reproduction. However, the way in which the pollen loads transported by pollinators and deposited on stigmas are affected by pollination context has been little studied. We investigated the impacts of plant mate and visiting insect availabilities on pollen transport and receipt in a mass‐flowering and facultative autogamous shrub (Rhododendron ferrugineum). First, we recorded insect visits to R. ferrugineum in plant patches of diverse densities and sizes. Second, we analyzed the pollen loads transported by R. ferrugineum pollinators and deposited on stigmas of emasculated and intact flowers, in the same patches. Overall, pollinators (bumblebees) transported much larger pollen loads than the ones found on stigmas, and the pollen deposited on stigmas included a high proportion of conspecific pollen. However, comparing pollen loads of emasculated and intact flowers indicated that pollinators contributed only half the conspecific pollen present on the stigma. At low plant density, we found the highest visitation rate and the lowest proportion of conspecific pollen transported and deposited by pollinators. By contrast, at higher plant density and lower visitation rate, pollinators deposited larger proportion of conspecific pollen, although still far from sufficient to ensure that all the ovules were fertilized. Finally, self‐pollen completely buffered the detrimental effects on pollination of patch fragmentation and pollinator failure. Our results indicate that pollen loads from pollinators and emasculated flowers should be quantified for an accurate understanding of the relative impacts of pollinator and mate limitation on pollen transfer in facultative autogamous species.     

Sunbird hovering behavior is determined by both the forager and resource plant

The long‐standing paradigm that pollination systems adapted to hovering birds evolved only in the New World was recently challenged by the discovery of hovering pollination by Old World specialized passerine pollinators. This raises the possibility that hovering pollination may evolve more easily than previously believed, given sufficient selective pressure on plant traits, on nectarivory, or both. We observed foraging behavior by the sunbird Cyanomitra oritis at flowers of the native Old World plant Impatiens sakeriana. We measured the length of pedicels and peduncles (PedPed length), which can make the flowers difficult to reach while the bird perches on the stem, and determined if it influenced sunbird hovering or perching at a flower. Detailed analyses of video recordings showed that sunbirds only hovered at flowers with a long PedPed, whereas they employed both foraging modes when an adequate perch was available. A hovering sunbird could deplete nectar in a shorter time than a perching one. The frequency of visits was not greater at flowers with longer PedPed or with more open I. sakeriana flowers in the vicinity. Our study provides evidence that sunbird behavior does not follow simple energetic models, and that some sunbird pollination systems in the Old World resemble highly specialized hummingbird systems in the New World much more than expected, especially the overall adaptation of the system to bird hovering.     

Pollinators shift to nectar robbers when florivory occurs,with effects on reproductive success in Iris bulleyana (Iridaceae)

• Studies have indicated that florivory and nectar robbing may reduce reproductive success of host plants. However, whether and how these effects might interact when plants are simultaneously attacked by both florivores and nectar robbers still needs further investigation.
• We used Iris bulleyana to detect the interactions among florivory, nectar robbing and pollination, and moreover, their effects on plant reproductive success. Field investigations and hand‐pollination treatments were conducted on two experimental plots from a natural population, in which Experimental plot was protected from florivores and Control plot was not manipulated.
• The flower calyx was bitten by sawflies to consume the nectary, and three bumblebee species were pollinators. In addition, the short‐tongued pollinator, Bombus friseanus, was the only robber when there was a hole made by a sawfly. The bumblebee had significantly shortened flower handling time when robbing, as compared to legitimate visits. Pollinator visitation and seed production decreased significantly in damaged flowers. However, seed production per flower after supplementary hand‐pollination did not differ significantly between damaged and undamaged flowers. Compared to the Experimental plot, bumblebees visited fewer flowers per plant in a foraging bout in the Control plot.
• The flowers damaged by florivory allowed B. friseanus to shift to a nectar robber. Florivory and nectar robbing collectively decreased plant reproductive success by consuming nectar resources, which may reduce attractiveness to pollinators of the damaged flowers. However, the changes in pollinator behaviour might be beneficial to the plant by reducing the risk of geitonogamous mating.

     

The pollination biology of Calypso bulbosa var. Americana (Orchidaceae): Initial deception of bumblebee visitors

Summary The orchid Calypso bulbosa var. americana has deceptive flowers that provide no rewards for visitors. Near Banff, Alberta, the flowering period of this species is synchronized with the emergence of its pollinators, large bumblebee queens, in late spring. Calypso flowers appear to rely on the initial attraction and deception of newly-emerged naive bumblebees for pollination. Indirect evidence suggests that individual bees subsequently learn to avoid these flowers and that avoidance is learned quite rapidly. Avoidance behavior by pollinators is obviously detrimental to sexual reproduction in Calypso. This negative effect appears to be offset by the large number of seeds produced in plants which are effectively pollinated. A test of the hypothesis that Calypso flowers mimic flowers of the shooting star, Dodecatheon radicatum (Primulaceae) failed to provide evidence for mimicry.     

A specialised pollination system using nectar‐seeking thynnine wasps in Caladenia nobilis (Orchidaceae)

• Caladenia is a diverse Australian genus that is exceptional among orchids in having both species pollinated by food‐seeking and sexually deceived insects. Here, we investigated the pollination of Caladenia nobilis, a species predicted to be food‐deceptive due to its large, cream‐coloured and apparently nectarless flowers.
• Pollinator observations were made using experimental clumps of flowers. Measurements of floral colour were undertaken with a spectrometer, nectar was tested using GC‐MS, and reproductive success was quantified for 2 years.
• While C. nobilis attracted nine species of insect, only males of the thynnine wasp Rhagigaster discrepans exhibited the correct size and behaviour to remove and deposit pollen. Male R. discrepans attempted to feed from the surface of the labellum, often crawling to multiple flowers, but showed no evidence of sexual attraction. Most flowers produced little or no nectar, although some may provide enough sucrose to act as a meagre reward to pollinators. Floral colouration was similar to a related Caladenia species pollinated by sexual deception, although the sexually deceptive species had a dull‐red labellum. Reproductive success was generally low and highly variable between sites and years.
• In addition to most visitors being of inappropriate size for pollinia removal, the lack of response to the orchid by several co‐occurring species of thynnine wasp suggests filtering of potential pollinators at the attraction phase. Our discovery of a pollination strategy that may be intermediate between food deception and food reward raises the question, how many putatively rewardless orchids actually produce meagre amounts of nectar?

     

Survival of Helicoverpa armigera larvae on and Bt toxin expression in various parts of transgenic Bt cotton (Bollgard II) plants

There is no conclusive evidence that Helicoverpa spp. (Lepidoptera: Noctuidae) in Australia have evolved significant levels of resistance to Bollgard II^® cotton (which expresses two Bt toxin genes, cry1Ac and cry2Ab). However, there is evidence of surviving larvae on Bollgard II cotton in the field. The distribution and survival of early‐instar Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) larvae were examined on whole Bollgard II and non‐Bt cotton plants in greenhouse bioassays. The expression of Cry toxins in various parts of Bollgard II plants was compared to the survival of larvae in those locations. Only 1% of larvae survived after 6 days on greenhouse‐grown Bollgard II plants compared to 31% on non‐Bt cotton plants. Overall, and across all time intervals, more larvae survived on reproductive parts (squares, flowers, and bolls) than on vegetative parts (leaves, stems, and petioles) on Bollgard II plants. The concentration of Cry1Ac toxin did not differ between plant structures, whereas Cry2Ab toxin differed significantly, but there was no relationship between the level of expression and the location of larvae. This study provides no evidence that lower expression of Cry toxins in the reproductive parts of plants explains the survival of H. armigera larvae on Bollgard II cotton.     

Spatio‐temporal patterns in pollination of deceptive Aristolochia rotunda L. (Aristolochiaceae)

• Pollination success of highly specialised flowers is susceptible to fluctuations of the pollinator fauna. Mediterranean Aristolochia rotunda has deceptive trap flowers exhibiting a highly specialised pollination system. The sole pollinators are kleptoparasitic flies in search of food. This study investigates these pollinators on a spatio‐temporal scale and the impact of weather conditions on their availability. Two potential strategies of the plants to cope with pollinator limitation, i.e. autonomous selfing and an increased floral life span, were tested.
• A total of 6156 flowers were investigated for entrapped pollinators in 10 Croatian populations. Availability of the main pollinator was correlated to meteorological data. Artificial pollination experiments were conducted and the floral life span was recorded in two populations according to pollinator availability.
• Trachysiphonella ruficeps (Chloropidae) was identified as dominant pollinator, along with less abundant species of Chloropidae, Ceratopogonidae and Milichiidae. Pollinator compositions varied among populations. Weather conditions 15–30 days before pollination had a significant effect on availability of the main pollinator. Flowers were not autonomously selfing, and the floral life span exhibited considerable plasticity depending on pollinator availability.
• A. rotunda flowers rely on insect pollen vectors. Plants are specialised on a guild of kleptoparasitic flies, rather than on a single species. Pollinator variability may result in differing selection pressures among populations. The availability/abundance of pollinators depends on weather conditions during their larval development. Flowers show a prolonged trapping flower stage that likely increases outcrossing success during periods of pollinator limitation.

     

Floral constraint resulting from intersexual mimicry in a gynodioecious fig tree

Fig trees (Ficus: Moraceae) are pollinated by female fig wasps (Agaonidae) whose larvae develop inside galled flowers of unusual inflorescences (figs). Most fig trees also support communities of non‐pollinating fig wasps. Figs of different species display great size variation and contain tens to tens of thousands of flowers. Around one‐half the species of fig trees have the gynodioecious breeding system, where female trees have figs that produce seeds and male trees have figs that support development of pollinators. Mutual mimicry between receptive male and female figs ensures that pollinators enter female figs, even though the insects will die without reproducing, but the need to give no sex‐specific cues to the pollinators may constrain differences in size between receptive male and female figs. We compared relationships between inflorescence size and some measures of reproductive success in male and female figs of Ficus montana grown under controlled conditions in the presence of the pollinator Kradibia tentacularis and its main parasitoid Sycoscapter sp. indesc. Female figs that contained more flowers produced more seeds, but male figs did not increase the production of female pollinator K. tentacularis fig wasps in proportion of the flower number. Although more flowers were galled by the pollinators in male figs containing more female flowers, the high larval mortality caused by parasitism and nutritional limitation prevented the increase in the production of adult female offspring. Selection may favor the increase in flower numbers within figs in female plants of F. montana, but contrarily constrain this attribute in male plants.     

Sex‐biased oviposition by a nursery pollinator on a gynodioecious host plant: Implications for breeding system evolution and evolution of mutualism

Dioecy, a breeding system where individual plants are exclusively male or female, has evolved repeatedly. Extensive theory describes when dioecy should arise from hermaphroditism, frequently through gynodioecy, where females and hermaphrodites coexist, and when gynodioecy should be stable. Both pollinators and herbivores often prefer the pollen‐bearing sex, with sex‐specific fitness effects that can affect breeding system evolution. Nursery pollination, where adult insects pollinate flowers but their larvae feed on plant reproductive tissues, is a model for understanding mutualism evolution but could also yield insights into plant breeding system evolution. We studied a recently established nursery pollination interaction between native Hadena ectypa moths and introduced gynodioecious Silene vulgaris plants in North America to assess whether oviposition was biased toward females or hermaphrodites, which traits were associated with oviposition, and the effect of oviposition on host plant fitness. Oviposition was hermaphrodite‐biased and associated with deeper flowers and more stems. Sexual dimorphism in flower depth, a trait also associated with oviposition on the native host plant (Silene stellata), explained the hermaphrodite bias. Egg‐receiving plants experienced more fruit predation than plants that received no eggs, but relatively few fruits were lost, and egg receipt did not significantly alter total fruit production at the plant level. Oviposition did not enhance pollination; egg‐receiving flowers usually failed to expand and produce seeds. Together, our results suggest that H. ectypa oviposition does not exert a large fitness cost on host plants, sex‐biased interactions can emerge from preferences developed on a hermaphroditic host species, and new nursery pollination interactions can arise as negative or neutral rather than as mutualistic for the plant.     

Comparative reproductive biology and pollinator specificity among sympatric Gomesa (Orchidaceae: Oncidiinae)

• The incredible pollination mechanisms displayed by orchid flowers has inspired biologists over the centuries. Based on the intriguing flower structures, the relationship among orchid species and their pollinators has been frequently regarded as very specialised.
• Given that visits on flowers pollinated by oil‐collecting bees are regularly rare, and in Oncidiinae the flowers frequently attractexclusively species that act as effective pollinators, the comparative reproductive biology and pollinator specificity of two sympatric Gomesa (G. varicosa and G. montana; Oncidiinae) were analysedbased on records of floral morphology, production of floral rewards, pollinators and pollination mechanisms. Furthermore, experimental pollinations were carried out in order to examine the breeding systems.
• The results have show that in the studied population, both Gomesa are visited by several bee species, but these orchids present a specific pollination system.Pollinaria are deposited on the head of Centridini (G. varicosa and G. montana) and Epicharitini (G. varicosa) bees when landed on the central callus of the labellumto collect lipoidal substances produced by glandular elaiophores on lateral lobes of the labellum. Both species are dependent on a biotic pollen vector to set fruits. Gomesamontana is completely self‐incompatible, while G. varicosa is partially self‐compatible.
• Our results indicate that although the occurrence of self‐sterile species seems to be common in Oncidiinae, in partially self‐incompatible species, as is the case of G. varicosa, self‐compatibility has been considered as an important factor favouring reproductive assurance in populations with low visitation frequencies, despite occurrence of inbreeding depression.

     

Floral volatile sesquiterpenes of Elsholtzia rugulosa (Lamiaceae) selectively attract Asian honey bees

There are few floral volatiles of compounds that have been properly assessed for attracting pollinators. The intense plant odour of Elsholtzia rugulosa (Lamiaceae) to humans may be attributed to the presence of high concentrations of β‐caryophyllene. In a previous study, Zhang, Yang, and Zhang (Scientific Reports, 6, 2016a, 276161) speculated that the presence of β‐caryophyllene attracts pollinators (e.g., honey bees) to its flowers, an assumption that was assessed through the exploration of the functional significance of specific floral volatile compounds and the evaluation of their effects on the behaviour of Apis cerana (Asian honey bees; a known pollinator) and two non‐pollinators, a hornet (Vespa velutina) and a bumblebee (Bombus sp.). The results from these behavioural experiments indicated that both β‐caryophyllene and β‐elemene (both naturally found in flowers of E. rugulosa) were individually attractive to the Asian honey bees. Moreover, the combination of the two was more effective than either of them separately. In contrast, neither compound, nor a blend of the two at different concentrations, was attractive to the hornet and bumblebee species. These results demonstrate that β‐caryophyllene and β‐elemene play a key signalling role in attracting Asian honey bees to E. rugulosa.     

Adaptive differentiation in floral traits in the presence of high gene flow in scarlet gilia (Ipomopsis aggregata)

Plant–pollinator interactions are thought to be major drivers of floral trait diversity. However, the relative importance of divergent pollinator‐mediated selection vs. neutral processes in floral character evolution has rarely been explored. We tested for adaptive floral trait evolution by comparing differentiation at neutral genetic loci to differentiation at quantitative floral traits in a putative Ipomopsis aggregata hybrid zone. Typical I. aggregata subsp. candida displays slender white tubular flowers that are typical of flowers pollinated by hawkmoths, and subsp. collina displays robust red tubular flowers typical of flowers pollinated by hummingbirds; yet, hybrid flower morphs are abundant across the East Slope of the Colorado Rockies. We estimated genetic differentiation (F_ST) for nuclear and chloroplast microsatellite loci and used a half‐sib design to calculate quantitative trait divergence (Q_ST) from collection sites across the morphological hybrid zone. We found little evidence for population structure and estimated mean F_ST to be 0.032. Q_ST values for several floral traits including corolla tube length and width, colour, and nectar volume were large and significantly greater than mean F_ST. We performed multivariate comparisons of neutral loci to genetic correlations within and between populations and found a strong signal for divergent selection, suggesting that specific combinations of floral display and reward traits may be the targets of selection. Our results show little support for historical subspecies categories, yet floral traits are more diverged than expected due to drift alone. Non‐neutral divergence for multivariate quantitative traits suggests that selection by pollinators is maintaining a correlation between display and reward traits.     

Floral morphology and pollination in Gastrodia elata,a mycoheterotrophic orchid

Pollination biology in Gastrodia elata was investigated on Rebun Island, Japan. The flowers have an urceolate perianth chamber whose opening is constricted by the column and labellum. This structure plays a crucial role in the selection of small‐bodied bees from flower visitors of various body sizes. In addition, the furrow on the ventral side of the column possibly contributes to the admission of sweat bee pollinators, whose thoracic widths match the width of the furrow. Sweat bees receive the pollinarium on their thorax while escaping head first from the chamber. No pollinator rewards, such as previously reported harvestable spongy tissue, are likely to be produced by the orchid. The flowers, however, have a glossy area reminiscent of nectar secreted into the chamber that likely acts as a deceptive signal for pollinators. Fruit‐set ratios were found to vary spatiotemporally; the values were higher under bright light conditions, probably reflecting the presence of sweat bees for sunny places.