Nocturnal Versus Diurnal Pollination Success in Isertia laevis (Rubiaceae): A Sphingophilous Plant Visited by Hummingbirds

Abstract: Isertia laevis (Rubiaceae) possesses flowers with traits typical for the pollination syndrome of sphingophily. Diurnal flower observation showed that nine different hummingbirds (Trochilidae) and one flower piercer (Coerebidae) were frequent visitors. Their activity on the flowers peaked in the morning hours. Very low nectar volumes were found in the morning (8.00 h) in unbagged flowers. Nectar volumes, however, reached their peaks (27 μl) at night (2.00 h) in bagged, as well as in unbagged flowers. At night few individuals of sphingids were observed. Pollination experiments showed that flowers presented to nocturnal pollinators from 18.00 h to 6.00 h had low fruit set (14 %) but high seed set (59 %). Flowers accessible from 6.00 h to 18.00 h for diurnal flower visitors showed high fruit set of 63 % but low seed set of 14 %. This suggests that pollination of individual flowers is less effective during daytime. Regarding relative reproductive success, i.e., efficiency of pollination defined as fruit set x seed set, both diurnal and nocturnal pollinators, however, are equally successful. We conclude that frequently occurring, but not very effective pollinators contribute substantially to seed production, when the expected pollinators are scarce.     

Genetic diversity and fine-scale genetic structure in Hancornia speciosa Gomes (Apocynaceae)

We studied the genetic diversity and spatial genetic structure (SGS) of adult and juvenile individuals in a population of Hancornia speciosa in Central-West Brazil. For this, we sampled and mapped 113 adults and 100 juveniles in an area of 2.5 ha. Genomic DNA was obtained from leaves and seven microsatellite loci were used to genotype all individuals. The studied population showed high genetic diversity (H_e) but with significant inbreeding (f) for both life stages most likely due to biparental inbreeding. Spatial genetic structure was weak for both life stages and the values of S_P were low and neighborhoods (Nb) was high for both generations showing a potential long-distance gene dispersal.     

Bimodal Pollination by Wasps and Beetles in the African Milkweed Xysmalobium undulatum

It has been suggested that flowers of some plants are specialized for pollination by two unrelated species (or functional groups) of pollinators. However, evidence for 'bimodal pollination systems' has been extremely limited. Studies of the milkweed Xysmalobium undulatum in South Africa showed that its flowers are visited by a range of different insects (representing 18 families), but only two groups, represented by the chafer beetle Atrichelaphinis tigrina and pompilid wasps in the genus Hemipepsis , effect pollination. Experiments showed that both these pollinator groups are effective in removing and inserting pollinia. Pollinia are attached to clypeal hairs and mouthparts on the wasps and tarsal hairs and spines on the beetles. Although considerably less abundant than the beetles, Hemipepsis spp. wasps move more quickly among flowers and appeared to be more effective pollinators overall. Experimental hand-pollinations conducted in the field showed that X. undulatum is genetically self-incompatible and thus completely reliant on pollinators for reproduction. We conclude that X. undulatum has a bimodal pollination system, specialized for pollination by Hemipepsis pompilid wasps and the chafer beetle A. tigrina .     

High specialisation in the pollination system of Mandevilla tenuifolia (J.C. Mikan) Woodson (Apocynaceae) drives the effectiveness of butterflies as pollinators

Butterfly pollination in the tropics is considered somewhat effective or solely effective in a few plant species. In the present study, we tested the hypothesis that Mandevilla tenuifolia (Apocynaceae), which has floral attributes associated with psychophily, has strategies adapted to pollination by butterflies, restricting other floral visitors and making these insects act as efficient pollinators. We analysed the floral and reproductive biology of M. tenuifolia, as well as the frequency and efficiency of its flower visitors. M. tenuifolia is an herb whose flowers have strong herkogamy and secondary pollen presentation on the style head, which corresponds to 60.4% of pollen on the anthers. Flower longevity and the long period of receptivity of the stigmatic region associated with the large amount of pollen removed in the first visits suggest that flowers remain functionally female during part of anthesis. Butterflies, mainly of the families Nymphalidae and Pieridae, are the only pollinators of M. tenuifolia. Despite being self‐compatible, M. tenuifolia depends on biotic vectors for fruit production. A non‐significant difference in fruit set between controlled treatments and natural conditions suggests that the pollinators are efficient. The inclination resulting from the landing of butterflies on flowers, together with flower morphology, guiding the insect proboscis inside the floral tube, as well as the frequency and efficiency of butterfly visits, are evidence of the close relationship between butterflies and M. tenuifolia, and also of the efficiency of these insects as pollinators.     

Pollination Ecology and Effect of Nectar Removal in Macleania bullata (Ericaceae)1

The floral syndrome of Macleania bullataYeo (Ericaceae) reflects its adaptation to hummingbird pollination. Its flowers, however, are subject to high levels of nectar robbing. I examined the floral visitor assemblage of M. bullata in a tropical montane wet forest in southwestern Colombia, focusing on the behavior of the visitors. I also tested for the presence of nocturnal pollination and the effects of nectar removal on new nectar production. The principal floral visitors were the nectar robbing hummingbirds Ocreatus underwoodii (19.1% of visits) and Chlorostilbon mellisugus (18.9%). Only two species of long–billed hummingbirds visited the flowers of M. bullata as “legitimate” pollinators: Coeligena torquata (14.7% of visits) and Doryfera ludoviciae (14.3%). The remaining visits constituted nectar robbing by bees, butterflies, and other species of hummingbirds. Nocturnal pollination took place, although fruit set levels were 2.4 times higher when only diurnal pollination was allowed as opposed to exclusively nocturnal pollination. Nectar robbers removed floral nectar without pollinating the flower. Treatments of experimental nectar removal were carried out to examine if flowers synthesize more nectar after nectar removal. Nectar removal increased the total volume of nectar produced by each flower without affecting sugar concentration. Thus, nectar robbing can impose a high cost to the plants by forcing them to replace lost nectar.     

Pollination and Breeding System of two Co-Occurring Hirtella Species (Chrysobalanaceae) in Central Brazil

The phenology, major floral characteristics, breeding systems and fruiting success of two co-occurring species of Hirtella: H. glandulosa and H.gracilipes (Chrysobalanaceae) were studied in Central Brazil. The two species occur as trees in mesophyllous forests but H. glandulosa is frequent also in dense savanna areas. Both species flower at the end of the dry season (September) and have flowers with one-day longevity. In both species flowers produce nectar and are pollinated exclusively by butterflies. The number of visits recorded and pollination rate in each species were significantly different and indicate that pollinators prefer H. glandulosa flowers. Natural and controlled fruit sets were low in both species. The index of self-incompatibility (ISI) was 0.17 in H. glandulosa and 0.86 in H. gracilipes. Although ISI in H. glandulosa could denote an incompatibility system, the presence of fruits with aborted embryos at different degrees of development point to an inbreeding depression situation. Low pollen viability and fruit set in H. gracilipes suggested reproductive problems which may be linked to hybridization events.     

Differential pollinator effectiveness and importance in a milkweed (Asclepias, Apocynaceae) hybrid zone

? Premise of the study: Exceptions to the ideal of complete reproductive isolation between species are commonly encountered in diverse plant, animal, and fungal groups, but often the causative ecological processes are poorly understood. In flowering plants, the outcome of hybridization depends in part on the effectiveness of pollinators in interspecific pollen transport. In the Asclepias exaltata and A. syriaca (Apocynaceae) hybrid zone in Shenandoah National Park, Virginia, extensive introgression has been documented. The objectives of this study were to (1) determine the extent of pollinator overlap among A. exaltata, A. syriaca, and their hybrids and (2) identify the insect taxa responsible for hybridization and introgression. ? Methods: We observed focal plants of parental species and hybrids to measure visitation rate, visit duration, and per-visit pollinia removal and deposition, and we calculated pollinator effectiveness and importance. ? Key results: Visitation rates varied significantly between the 2 yr of the study. Overall, Apis mellifera, Bombus sp., and Epargyreus clarus were the most important pollinators. However, Bombus sp. was the only visitor that was observed to both remove and insert pollinia for both parent species as well as hybrids. ? Conclusions: We conclude that Bombus may be a key agent of hybridization and introgression in these sympatric milkweed populations, and hybrids are neither preferred nor selected against by pollinators. Thus, we have identified a potential mechanism for how hybrids act as bridges to gene flow between A. exaltata and A. syriaca. These results provide insights into the breakdown of prezygotic isolating mechanisms.     

Coexistence of Delayed Autonomous Self pollination and Deceptive Pollination in Arthropodium cirratum (Asparagaceae)

Delayed autonomous pollination and deceptive pollination are assumed to be relatively common in flowering plants, but no species have been reported to use both of these cunning reproductive strategies. In this study, we examined whether delayed selfing and mimicry were used concurrently in Arthropodium cirratum. Flowers of A.cirratum were manipulated to assess whether their stamen appendages and corolla closing movements were functional in deceptive pollination and delayed selfing, respectively. Our results indicated that anther or pollen imitation of the yellow stamen appendages contributed to 93 per cent of successful mimetic attraction, and this mimicry was an important driver of cross pollination of the species. In addition, we observed closure of the perianth relocated the stamens over the stigma at the end of anthesis, which significantly increased the average seed number per fruit of intact flowers over flowers emasculated before closure (20.62 versus 11.79). Our findings confirmed the coexistence of delayed autonomous self pollination and deceptive pollination in A.cirratum. Our results also suggested that delayed selfing could add fitness benefits for this mimetic attraction species.     

Pollination of Pteroglossaspis ruwenzoriensis (Rendle) Rolfe (Orchidaceae) by Beetles in Argentina

Beetle pollination by Euphoria lurida (Scarabaeidae: Cetoninae) is documented for Pteroglossaspis ruwenzoriensis (Orchidaceae: Epidendroideae: Cymbideae: Eulophiinae) in its natural habitat in Central Argentina (South America). Flower features with special emphasis on those related to beetle pollination are given. These include: long rigid and well exposed inflorescences, sturdy inconspicuous and deep flowers with small entrance, emission of a yeast-like fragrance, jelly-like nectar, short column, and a head-attaching pollinarium with a broad saddle-like viscidium. Pollinator behaviour and pattern of flower opening favour cross pollination and probably long distance pollen dispersal. Flowering, which lasts about 3 weeks, peaks in summer past mid-January. In natural conditions about 68 flowers are pollinated for every 100 pollinaria removals.     

Isolation, characterization and cross-amplification of polymorphic microsatellite loci in Laelia speciosa (Orchidaceae)

Laelia speciosa is an endangered epiphytic orchid endemic to central Mexico. Here, we report on the development of 14 perfect and imperfect microsatellite repeat loci for this species. Numbers of alleles ranged from two to 16 and levels of observed heterozygosities among the 14 loci ranged from 0.28 to 1.00 across two widely divergent populations. All loci were also tested for cross-amplification in four other Laelia species and other selected genera of the subtribe Laeliinae.     

Pollination by flies, bees, and beetles of Nuphar ozarkana and N. advena (Nymphaeaceae)

Nuphar comprises 13 species of aquatic perennials distributed in the temperate Northern Hemisphere. The European species N. lutea and N. pumila in Norway, the Netherlands, and Germany are pollinated by bees and flies, including apparent Nuphar specialists. This contrasts with reports of predominant beetle pollination in American N. advena and N. polysepala. We studied pollination in N. ozarkana in Missouri and N. advena in Texas to assess whether (1) there is evidence of pollinator shifts associated with floral-morphological differences between Old World and New World species as hypothesized by Padgett, Les, and Crow (American Journal of Botany 86: 1316-1324. 1999) and (2) whether beetle pollination characterizes American species of Nuphar. Ninety-seven and 67% of flower visits in the two species were by sweat bees, especially Lasioglossum (Evylaeus) nelumbonis. Syrphid fly species visiting both species were Paragus sp., Chalcosyrphus metallicus, and Toxomerus geminatus. The long-horned leaf beetle Donacia piscatrix was common on leaves and stems of N. ozarkana but rarely visited flowers. Fifteen percent of visits to N. advena flowers were by D. piscatrix and D. texana. The beetles' role as pollinators was investigated experimentally by placing floating mesh cages that excluded flies and bees over N. advena buds about to open and adding beetles. Beetles visited 40% of the flowers in cages, and flowers that received visits had 69% seed set, likely due to beetle-mediated geitonogamy of 1st-d flowers. Experimentally outcrossed 1st-d flowers had 62% seed set, and open-pollinated flowers 76%; 2nd-d selfed or outcrossed flowers had low seed sets (9 and 12%, respectively). Flowers are strongly protogynous and do not self spontaneously. Flowers shielded from pollinators set no seeds. A comparison of pollinator spectra in the two Old World and three New World Nuphar species studied so far suggests that the relative contribution of flies, bees, and beetles to pollen transfer in any one population depends more on these insects' relative abundances (and in the case of Donacia, presence) and alternative food sources than on stamen length differences between Old World and New World pond-lilies.     

Pollination in Jacaranda rugosa (Bignoniaceae): euglossine pollinators, nectar robbers and low fruit set

Nectar robbers access floral nectar in illegitimate flower visits without, in general, performing a pollination service. Nevertheless, their effect on fruit set can be indirectly positive if the nectar removal causes an incremental increase in the frequency of legitimate flower visits of effective pollinators, especially in obligate outcrossers. We studied pollination and the effect of nectar robbers on the reproductive fitness of Jacaranda rugosa , an endemic shrub of the National Park of Catimbau, in the Caatinga of Pernambuco, Brazil. Xenogamous J . rugosa flowers continuously produced nectar during the day at a rate of 1 μl·h⁻¹. Female and male Euglossa melanotricha were the main pollinators. Early morning flower visits substantially contributed to fruit set because stigmas with open lobes were almost absent in the afternoon. Ninety-nine per cent of the flowers showed damage caused by nectar robbers. Artificial addition of sugar water prolonged the duration of flower visits of legitimate flower visitors. Removal of nectar, simulating the impact of nectar robbers, resulted in shorter flower visits of euglossine bees. While flower visits of nectar-robbing carpenter bees ( Xylocopa frontalis , X . grisescens, X . ordinaria) produced only a longitudinal slit in the corolla tube in the region of the nectar chamber, worker bees of Trigona spinipes damaged the gynoecium in 92% of the flowers. This explains the outstandingly low fruit set (1.5%) of J. rugosa in the National Park of Catimbau.     

Performance of marking techniques in the field and laboratory for Diabrotica speciosa (Germar) (Coleoptera: Chrysomelidae)

A reliable marking technique was needed for a mark–release–recapture experiment with adults of Diabrotica speciosa (Germar). Four marking techniques, acrylic paint (spattered or brushed on the surface of the insect); and fluorescent pigments (dusted on surfaces or mixed with diet to produce an ingested marker), were tested. Fluorescent pigment durability for the dusting and ingested techniques was evaluated for laboratory conditions and under simulated field conditions. The impact of the techniques on beetle survival was also assessed. Both acrylic paint techniques caused mobility problems in the beetles, and neither technique lasted for more than 48 h. Both fluorescent pigment techniques were more reliable, but the dusting technique showed a significantly higher mortality than the control, and duration variations between laboratory and field conditions. Use of fluorescent pigments added to the diet was the most reliable technique. This technique allowed the manipulation of the marking period, and provided reliable timing of marker persistence in the field.     

Pollination and late-acting self-incompatibility in Cyrtanthus breviflorus (Amaryllidaceae): implications for seed production

Background and Aims

Animal pollination is typically an uncertain process that interacts with self-incompatibility status to determine reproductive success. Seed set is often pollen-limited, but species with late-acting self-incompatibility (SI) may be particularly vulnerable, if self-pollen deposition results in ovule discounting. Pollination is examined and the occurrence of late-acting SI and ovule discounting assessed in Cyrtanthus breviflorus.

Methods

The pollination system was characterized by observing floral visitors and assessing nectar production and spectral reflectance of flowers. To assess late-acting SI and ovule discounting, growth of self- and cross-pollen tubes, and seed set following open pollination or hand pollination with varying proportions of self- and cross-pollen, were examined.

Key Results

Native honeybees Apis mellifera scutellata pollinated flowers as they actively collected pollen. Most flowers (≥70 %) did not contain nectar, while the rest produced minute volumes of dilute nectar. The flowers which are yellow to humans are visually conspicuous to bees with a strong contrast between UV-reflecting tepals and UV-absorbing anthers and pollen. Plants were self-incompatible, but self-rejection was late-acting and both self- and cross-pollen tubes penetrated ovules. Seed set of open-pollinated flowers was pollen-limited, despite pollen deposition exceeding ovule number by 6-fold. Open-pollinated seed set was similar to that of the cross + self-pollen treatment, but was less than that of the cross-pollen-only treatment.

Conclusions

Flowers of C. breviflorus are pollinated primarily by pollen-collecting bees and possess a late-acting SI system, previously unknown in this clade of the Amaryllidaceae. Pollinators of C. breviflorus deposit mixtures of cross- and self-pollen and, because SI is late-acting, self-pollen disables ovules, reducing female fertility. This study thus contributes to growing evidence that seed production in plants with late-acting SI systems is frequently limited by pollen quality, even when pollinators are abundant.     

红豆杉的胚珠发育,传粉滴形成和传粉过程

观察了红豆杉（Ｔａｘｕｓ ｃｈｉｎｅｎｓｉｓ （Ｐｉｌｇ．）Ｒｅｈｄ）的花粉形态和水合特性及胚珠发育、传粉滴形成与传粉过程。成熟花粉为单细胞,无气吓,形状不规则,外壁表面具大量乌氏体。花粉水合时,内壁膨胀,外壁开裂。通常情况下,外壁保留在水滴或传粉滴的表面,而花粉的其他部分进入水滴或传粉滴内。在８月下旬,可观察到下弯的雌性生殖芽。下弯这一特性是雌性生殖芽区别于营养芽的重要特征。这一时期的雌性生殖芽     

Pollination and Predation Limit Fruit Set in a Shrub,Bourreria succulents (Boraginaceae), after Hurricanes on San Salvador Island,Bahamas1

Hurricanes have been assumed to reduce the reproduction of plants, either directly by leaf stripping and stress or indirectly by reducing pollinators. I examined the pollination and fruit set of a common shrub, Bourreria succulenta, after hurricanes on San Salvador island, Bahamas. Contrary to the assumption of resource limitation, B. succulenta showed unusually prolific flowering after Hurricane Lili stripped leaves from most of the plants in October 1996. I predicted that the abundant flowering would saturate pollinators and that fruit set would be pollination‐limited. Fruit set was strongly pollination‐limited by 71 percent. Butterflies are probably the major pollinators and were present at the site, but they rarely visited B. succulenta flowers even though flowers were brimming with nectar. Nectarivorous birds (Bananaquits and Bahama Wbodstars) visit B. succulenta flowers, but their populations were decimated by Hurricane Lili and they rarely visited flowers during this time. Fruit set was also severely predation‐limited; a moth caterpillar (Gelechiidae) was extremely abundant and ate buds, flowers, and fruits, causing a further 68 percent reduction in fruit set. Together, pollination limitation and predation limitation reduced fruit set to only 7 percent or less. Predation was also intense in 1999 after Hurricane Floyd and resulted in 11 percent fruit set or less. Whether or not hurricanes were the cause of limited pollinators or abundant predators, the resulting low fruit set could have population effects because hurricanes can provide opportunities for the recruitment of new plants. These results emphasize that understanding plant–animal interactions may be necessary for predicting the effects of hurricanes on plant reproductive success, which may affect subsequent recruitment. Species on small islands like San Salvador (150 km²) with relatively few species may be especially vulnerable to environmental disturbances such as hurricanes.