Putative Pollinators Research Articles

SUGAR PREFERENCES OF THE GREEN-BACKED FIRECROWN HUMMINGBIRD (SEPHANOIDES SEPHANIODES): A FIELD EXPERIMENT

Many flowers associated with hummingbirds (Trochilidae) produce nectar rich in sucrose, a characteristic that reflects innate preferences or the metabolic capacities of their putative pollinators or both. However, studies on nectar sugar selectivity by hummingbirds in the field are lacking. Under natural field conditions, we studied the sugar preferences of the Green-backed Firecrown Hummingbird (Sephanoides sephaniodes), the southernmost hummingbird in the world and a key pollinator in the temperate forest of South America. We considered potential differences between males and females and the influence of environmental temperature on those preferences. To free-foraging Green-backed Firecrown Hummingbirds, we simultaneously offered four different sugar solutions with the same concentration (24% wt/wt): (1) sucrose, (2) glucose, (3) fructose, and (4) a 1:1:1 mixture of these three solutions, as well as a control of pure water. The experimental design involved three replicates per treatment assigned to three different “blocks” of five feeders each, during eight periods of seven days each. We scored the number of Green-backed Firecrown Hummingbirds feeding on each feeder, the number of consumptions made by each individual, and the amount of sugar (g) consumed per sampling period. Green-backed Firecrown Hummingbirds clearly discriminated against pure water, favoring sugar solutions; of the latter, they preferred sucrose over glucose and fructose. The mixed-sugar solution showed intermediate preference values. Neither sex nor temperature affected sugar preferences. Sugar preferences by the Green-backed Firecrown Hummingbird could influence the nectar composition of the flowers it pollinates through differential selection. Preferencia de Azúcares en Sephanoides sephaniodes: un Experimento de Campo

Generalised pollination of Diuris alba (Orchidaceae) by small bees and wasps

Most Diuris species possess flowers of pea-like form and colour, and occur in association with flowering peas of the tribe Mirbeliae. Previous studies of the pollination of Diuris maculata sensu lato have found evidence for guild mimicry of pea flowers. The flowers of Diuris alba are also pea-like in form but not in colour, and this species is frequently found in habitats where peas are uncommon or absent. We investigated the pollination of Diuris alba, which we expected may have a distinct pollination system at Lake Munmorah, New South Wales. Many Diuris species lack floral rewards, but D. alba produced a small amount of nectar. Flower visitors, and hence putative pollinators, were mainly female Exoneura bees, but also the wasps Eurys pulcher and a Paralastor species. Reproductive success of D. alba, both in woodland containing abundant Dillwynia retorta and in heathland where this pea was absent, was higher than in the previously studied D. maculata s.l. We suggest that the pollination of D. alba is more generalised than that found in the legume guild mimic D. maculata s.l. Although its flowers may display structural similarity to pea flowers, other characteristics suggest that its pollination system has diverged from a presumed pea-mimicry ancestral condition.

Are Phenological Observations Sufficient to Estimate the Quality of Seed Crops from a Eucalyptus grandis Open-pollinated Seed Orchard? Consequences for Seed Collections

Reproductive phenology was observed over three years in a Eucalyptus grandis seed orchard in Madagascar to determine the impact of geographic differences of parental selections on the expected genetic composition of seed crops. Pollen flow (observed pollen cloud) was deduced from a paternity assignment based on sampling from one year’s seed production. The two approaches were used to verify whether knowledge of phenology is sufficient to predict the genetic quality of the seeds collected. Despite the high flowering level, with a constant cycle over three years, the results demonstrated wide reproductive phenological differences associated with the parents’ origin, suggesting putative pollination disequilibrium. From both observed and expected pollen clouds, the results showed preferential mating among different provenances, which has consequences for seed crop composition. Phenological observations, which can be made inexpensively, can be used to promote methods of effective seed orchard management in order to improve the genetic quality of seeds.

Pollinator visitation, pollen limitation, and selection on flower size through female function in contrasting habitats within a population of Campanula persicifolia

We looked at whether flower visitation rates, pollen limitation on seed production, and phenotypic selection on flower size through female function varied across a sharp gradient in light intensity (open meadow vs. forest) within a population of the perennial plant Campanula persicifolia L. (Campanulaceae). Flower visitation rates of putative pollinators were similar in both habitats. Seed number per fruit was strongly pollen limited, with no difference in the magnitude of pollen limitation between the two habitats. This strong pollen limitation set the basis for significant phenotypic selection, through female function, on a trait that probably is important for pollinator attraction: flower size. This was revealed by path analysis and structural equation modelling. The lack of difference in pollen limitation on seed production in the two habitats may be explained by the similarity in flower visitation rates in the two habitats. Moreover, the similarity in pollen limitation in the two habitats probably resulted in a similar magnitude and direction of selection on flower size through female function. Our results suggest that pollen limitation and selection through female function may vary little across space within a popualtion despite large variation in the environmental conditions experienced by plants.

Anther Cap Retention Prevents Self-pollination by Elaterid Beetles in the South African Orchid Eulophia foliosa

Pollination by insects that spend long periods visiting many flowers on a plant may impose a higher risk of facilitated self-pollination. Orchids and asclepiads are particularly at risk as their pollen is packaged as pollinia and so can be deposited on self-stigmas en masse. Many orchids and asclepiads have adaptations to limit self-deposition of pollinia, including gradual reconfiguration of pollinaria following removal. Here an unusual mechanism--anther cap retention--that appears to prevent self-pollination in the South African orchid Eulophia foliosa is examined. Visits to inflorescences in the field were observed and pollinators collected. Visitation rates to transplanted inflorescences were compared between a site where putative pollinators were abundant and a site where they were rare. Anther cap retention times were determined for removed pollinaria and atmospheric vapour pressure deficit was recorded concurrently. Anther cap anatomy was examined using light microscopy. Eulophia foliosa is pollinated almost exclusively by Cardiophorus obliquemaculatus (Elateridae) beetles, which remain on the deceptive inflorescences for on average 301 s (n = 18). The anther cap that covers the pollinarium is retained for an average of 512 s (n = 24) after pollinarium removal by beetles. In all populations measured, anther cap dimensions are greater than those of the stigmatic cavity, thus precluding the deposition of self-pollinia until after the anther cap has dropped. An anatomical investigation of this mechanism suggests that differential water loss from regions of the anther cap results in opening of the anther cap flaps. This is supported by observations that as atmospheric vapour pressure deficits increased, the duration of anther cap retention was reduced. Flowers of E. foliosa are specialized for pollination by elaterid beetles. Retention of anther caps for a period exceeding average visit times by beetles to inflorescences appears to prevent facilitated self-pollination in E. foliosa effectively.

Pollination ecology of four epiphytic orchids of New Zealand.

In New Zealand epiphytic orchids are represented by four genera and eight species. The genera Earina (three species) and Winika (one species) are the most conspicuous and widespread. These are likely to be some of the southernmost distributed genera of epiphytic orchids in the world. To identify the pollination strategies that have evolved in these orchids, hand-pollination treatments were done and floral visitors were observed in several wild populations at two areas of southern North Island (approx. 40 degrees S). Pollen:ovule ratio and osmophores were also studied and the total carbohydrate content of the nectar produced by each species was measured. Earina autumnalis and Earina mucronata are self-compatible, whereas Earina aestivalis and Winika cunninghamii appear to be partially self-incompatible. All four orchids are incapable of autonomous selfing and therefore completely dependent on pollinators to set fruits. Floral visitors observed in the genus Earina belong to Diptera, Coleoptera and Hymenoptera and to Diptera and Hymenoptera in W. cunninghamii. Contrary to many epiphytic orchids in the tropics, the orchid-pollinator relationship in these orchids is unspecialized and flowers are visited by a wide range of insects. Putative pollinators are flies of the families Bibionidae, Calliphoridae, Syrphidae and Tachinidae. All four orchids display anthecological adaptations to a myophilous pollination system such as simple flowers, well-exposed reproductive structures, easily accessed nectar and high pollen : ovule ratios.

Trap-flower fly pollination in East African Ceropegia L. (Apocynaceae)

Pollination in the genus Ceropegia L. (Apocynaceae: Asclepiadoideae- Ceropegieae) in East Africa is discussed based on field observations and herbarium studies. All inferred or confirmed pollinators are small, mostly female dipteran flies, c. 2.5 mm long, which carry pollinaria on their proboscis. Identified putative pollinator flies belong to families Milichiidae, Chloropidae and Ceratopogonidae. The most important factors for an insect to effect pollination appear to be the appropriate overall size, i.e. small size of c. 3 × 3 mm at most, and appropriate mouth parts, i.e. extendible probosces with suitable surfaces and adjacent pads on which a pollinarium can attach. The complex and diverse floral morphology of the tubular flowers and their disposition as well as other commonly occurring features namely, diverse interior and exterior coloration, diverse scents, secretions such as nectar and water droplets, vibratile corolla lobes and hairs, specialized hairs, interior sculpturing, sliding zones and differential lighting within the flower are important mechanisms for attracting and detaining insect pollinators.

Differential outcrossing rates in dispersing and non-dispersing achenes in the heterocarpic plant Crepis sancta (Asteraceae)

The association between mating systems and dispersal in plants has been studied mostly in cleistogamous species where, generally, seeds produced by cleistogamous (selfed) flowers are less dispersed than seeds produced by chasmogamous (potentially outcrossed) flowers. In heterocarpic Asteraceae, non-dispersing fruits (achenes) are produced at the periphery of the capitulum (outer florets) whereas dispersing achenes are produced by inner florets in the same capitulum. Since all the florets are protandrous, the outer floret developing first are in female phasis when anthesis of inner florets takes place. Thus, outer florets can be potentially selfed by the inner florets of the same capitulum whereas the latter must be pollinated by flowers of other capitula. Therefore outer florets should be more inbred than inner florets. To test this hypothesis, we measured the natural outcrossing rate in outer and inner florets using allozymes in three populations of the heterocarpic Crepis sancta. The results showed that the outcrossing rate was highest for non-dispersed achenes. Moreover, among the outcrossed achenes within a capitulum it was observed that the number of paternal parents of non-dispersing achenes was higher than for dispersing achenes. The pattern observed was therefore the opposite to the pattern of cleistogamous plants and contradicts the putative pollination mechanism we proposed for Asteraceae. The results agree with the predictions of sib competition theory which considers that outcrossing may minimize competitive interactions among relatives (sibs) falling near the mother plant. Higher outcrossing rate in outer florets could also occur because pollinators are more attracted to these florets.

Late steps of egg cell differentiation are accelerated by pollination in Zea mays L.

Egg cells were analysed cytologically during the female receptivity period in maize (Zea mays L., line A 188). Three classes of egg cell were distinguished: type A--small, non-vacuolated cells with a central nucleus; type B--larger cells with small vacuoles surrounding the perinuclear cytoplasm located in the middle of the cell; type C--big cells with a large apical vacuole and the mid-basal perinuclear cytoplasm. The less-dense cytoplasm of the vacuolated egg cells usually contained numerous cup- or bell-shaped mitochondria. The three egg types appear to correspond to three late stages of egg cell differentiation. The frequencies of each of the three egg types were monitored in developing maize ears before and after pollination. In young ears, with the silks just extending out of the husks, small A-type cells were found in about 86% of ovules. Their frequency decreased to about 58% at the optimum silk length, remained unchanged in non-pollinated ears, and fell to 16% at the end of the female receptivity period. However, after pollination and before fertilisation the frequency of these cells decreased to about 33%, and the larger vacuolated egg cells (types B and C) prevailed. At various stages of the receptivity period, pollination accelerated changes in the egg population, increasing the number of ovules bearing larger, vacuolated egg cells. Experiments with silk removal demonstrated that putative pollination signals act immediately after pollen deposition and are not species-specific.

Observations of putative pollinators of Hemipilia flabellata Bur. et Franch. (Orchidaceae) in north-west Yunnan Province, China

Interactions between Hemipilia flabellata and anthophilous insects were studied in north-western Yunnan, China during June–July of 1996 and 1997. Twenty-seven species of insects were seen visiting the flowers of this species, although only male and female individuals of the bee Anthophora mangkamensis Wu were observed carrying the pollinaria. The frequency of visits by A. mangkamensis to this orchid was rather low. Pollinating bees normally sampled only the lowermost flowers in an inflorescence, staying for 1–3 seconds. This species is also characterized by low pollination, low fruit set (1–22%) and a very striking decrease in fruit production from bottom to top of the inflorescence. All of these indicate that the orchid may rely on deception to attract visitors. Ajuga forrestii Diels (Labiatae) appears to be the main or exclusive subsidiary nectar source for A. mangkamensis during the flowering period ofH. flabellata. It appears that H. flabellata utilizes a food deceit pollination strategy for pollination. The orchid benefits from the great variation of flowers in colour and shape. Phenological, functional-morphometric and distribution data indicate that A. mangkamensis is an optimal pollinator of H. flabellata and thus the anthecological adaptation of the orchid to the pollen vector may be unique.

Observations of putative pollinators of Hemipilia flabellata Bur. et Franch.(Orchidaceae) in north-west Yunnan Province, China

Interactions between Hemipilia flabellata and anthophilous insects were studied in northwestern Yunnan, China during June‐July of 1996 and 1997. Twenty-seven species of insects were seen visiting the flowers of this species, although only male and female individuals of the bee Anthophora mangkamensis Wu were observed carrying the pollinaria. The frequency of visits by A. mangkamensis to this orchid was rather low. Pollinating bees normally sampled only the lowermost flowers in an inflorescence, staying for 1‐3 seconds. This species is also characterized by low pollination, low fruit set (1‐22%) and a very striking decrease in fruit production from bottom to top of the inflorescence. All of these indicate that the orchid may rely on deception to attract visitors. Ajuga forrestii Diels (Labiatae) appears to be the main or exclusive subsidiary nectar source for A. mangkamensis during the flowering period of H. flabellata. It appears that H. flabellata utilizes a food deceit pollination strategy for pollination. The orchid benefits from the great variation of flowers in colour and shape. Phenological, functional-morphometric and distribution data indicate that A. mangkamensis is an optimal pollinator of H. flabellata and thus the anthecological adaptation of the orchid to the pollen vector may be unique.

Seed Production, Pollinator Attractants and Breeding System in Relation to Fire Response — Are There Reproductive Syndromes among Co-occurring Proteaceous Shrubs?

The reproductive biology of two species pairs was compared, one member of which (Dryandra sessilis (Knight) Domin, Hakea erinacea Meissner) is susceptible to severe stress and disturbance by fire (nonsprouter) and stores few seeds in its crown, while the other (D. lindleyana Meissner, H. cristata R.Br.) is resilient (resprouter) and also stores most of its seeds for some years. It was hypothesised that the nonsprouter would have a high annual seed production associated with a suite of attributes directed towards that end (forming a reproductive syndrome), and that the resprouter would have the reverse properties. Over 30 attributes were assessed, covering putative pollinators, pollinator attractants and rewards, flower phenology, breeding system, and flower, fruit and seed production. Dryandra sessilis produced far more seeds than D. lindleyana, due to prolific flower production and a high fruit : flower ratio (associated with an effective outcrossing breeding system). Hakea erinacea produced significantly more seeds than H. cristata, which was attributable to its smaller fruits and exceptionally high fruit : flower ratio (associated with highly effective selfing). The correlation of seed production and fruit : flower ratio with susceptibility to fire was not supported by any consistent pattern among the other reproductive attributes.

Demonstration of Pollinator-Mediated Reproductive Isolation in Sexually Deceptive Species of Chiloglottis (Orchidaceae: Caladeniinae)

Three designs of field choice experiments were used to demonstrate complete reproductive isolation by sexually deceived thynnine pollinators (Neozeleboria Rohwer spp.) in eight species of Chiloglottis R.Br. Four species, Chiloglottis diphylla R.Br., C. formicifera Fitzg., C. pluricallata D.L.Jones and C. valida D.L.Jones, attracted only one wasp species, but the other four, C. platyptera D.L.Jones, C. seminuda D.L.Jones, C. trilabra Fitzg. and C. reflexa Labill. Druce exhibited multiple species attraction. Wasps visiting orchids were classified as major responders if they exhibited behaviour which could potentially result in pollination, by contrast to minor responders which did not. Major responders occurring sympatrically with the orchid were termed confirmed, potential or putative pollinators on the basis of observation of pollinia removal or deposition, pseudocopulation with the labellum, or arrival at bait flowers with pollinia from local orchid populations, respectively. Each Chiloglottis species had a single Neozeleboria species as confirmed or potential pollinator. The data confirmed that field pollinator choice tests can be used to distinguish cryptic sexually deceptive orchid species, and that specific pollinators may be used reliably as taxonomic characters in Chiloglottis.

Pollination of Angiosperms in Contrasting Coniferous Forests

We studied the distributions of flower color, flower morphology, and putative pollinators in eight communities in the western Cascades of Washington and 14 communities in the eastern Cascades. These two forested regions differ in the proportions of species in each flower color and morphological type such that the eastern region is more complex. The putative pollinators of each species were determined from morphological and color properties of the flowers and from the recent, extensive literature. The floristic complement of the western region appears to be serviced by a collection of pollinators that is less diverse than that of the east. In each region there is a strong positive correlation between species richness and flower color diversity, floral morphology diversity, and putative pollinator diversity, respectively. These comparisons suggest the competition for pollinators has led to greater niche differentiation in the eastern regions and that this factor, combined with greater habitat complexity, results in the far greater species richness of the eastern region.

POLLINATION OF ANGIOSPERMS IN CONTRASTING CONIFEROUS FORESTS

We studied the distributions of flower color, flower morphology, and putative pollinators in eight communities in the western Cascades of Washington and 14 communities in the eastern Cascades. These two forested regions differ in the proportions of species in each flower color and morphological type such that the eastern region is more complex. The putative pollinators of each species were determined from morphological and color properties of the flowers and from the recent, extensive literature. The floristic complement of the western region appears to be serviced by a collection of pollinators that is less diverse than that of the east. In each region there is a strong positive correlation between species richness and flower color diversity, floral morphology diversity, and putative pollinator diversity, respectively. These comparisons suggest the competition for pollinators has led to greater niche differentiation in the eastern regions and that this factor, combined with greater habitat complexity, results in the far greater species richness of the eastern region.

Convergent Floral Evolution in South African and Australian Proteaceae and Its Possible Bearing on Pollination by Nonflying Mammals

Convergent Floral Evolution in South African and Australian Proteaceae and Its Possible Bearing on Pollination by Nonflying Mammals