Pollination of four sympatric species ofAngelonia (Scrophulariaceae) by oil-collecting bees in NE. Brazil

The manner whereby the oil-producing bisaccate flowers ofAngelonia (Scrophulariaceae) are pollinated by female oil-collecting bees is reported for the first time. Observations were made in the Caatinga formation of Pernambuco, NE. Brazil, on four synchronopatric species. These differ in sizes and structural details of the corolla, level of flower exposition, and habitat preferences. All legitimate visitors wereCentris spp. (Anthophoridae):Angelonia hirta was mainly pollinated byC. fuscata andA. pubescens byC. hyptidis; A. bisaccata andA. hookeriana shared an unidentified species. Several exomalopsine, tetrapediine and meliponid bees exploit the flowers less descriminately for oil or pollen, respectively, without regularly contacting anthers and stigma. The flowers are protandrous, and are self-incompatible except those of the annualA. pubescens. After alighting, theCentris bees introduce their front legs simultaneously into each of the pouches and start alternate collecting movements to gather the oil from the trichome elaiophores. While doing so, they are forced by projections of the corolla floor to press their head under the anthers and stigma, whereby pollen is transferred with their frons or clypeus. On account of their collector type and behaviour,C. fuscata andC. spec. are not specialized toAngelonia but may equally exploit other nonrelated taxa for oil, whereasC. hyptidis exhibits oligolecty onA. pubescens. It possesses relatively elongate forelegs with padlike collectors suitable for sweeping the lipids from the scattered glandular hairs inside the divergent spurs of its host. It is the only species that also collects pollen (by buzzing) from the oil host.A. hirta and relatives, provided with dense elaiophore carpets, are, for their part, adapted to scrapingCentris species with typical oil collectors. Flower and bee phenologies, although largely dependent on the irregular rainfalls, are not always coincident.     

Interaction between oil-collecting bees and seven species of Plantaginaceae

Oil-bee/oil-flower mutualism evolved through multiple gains and losses of the ability to produce floral oil in plants and to collect it in bees. Around 2000 plant species are known to produce floral oils that are collected by roughly 450 bee species, which use them for the construction of nests and for the larval food. The Plantaginaceae contain several Neotropical species that produce floral oils, the main reward offered by these plants. In the genera Angelonia, Basistemon, Monopera and Monttea, mainly associated with Centris bees, the floral oil is produced in trichomes that are located in the inner corolla. The pollinators of a few species in this neotropical clade of Plantaginaceae are known, and the role of flower morphology as well as the requirements from pollinators and the role of other groups of bees in the pollination of these flowers remains unclear. In this paper we provide a list of the flower visitors of seven Plantaginaceae species (six Angelonia species and Basistemon silvaticus) analyzing their behavior to highlight the legitimate pollinators and illustrating little known aspects of flower morphology and oil-collecting apparatuses of the bees. Two general morphological patterns were observed in the Angelonia flowers: deep corolla tube with short lobes, and short corolla tube with long lobes. Corolla tubes of different length result in pollen adherence to different parts of the insect body. The six Angelonia species and B. silvaticus flowers were visited by 25 oil-collecting bee species (10 Centris, 11 Tapinotaspidini and 4 Tetrapedia species), the majority acting as legitimate visitors. The flowers were also visited by illegitimate bee pollinators, which collected pollen but do not transfer it to the female organ. Specialized collectors of Plantaginaceae floral oils present modifications on the first pair of legs, mainly in the basitarsi but also extended to the tarsomeres. The new records of Tapinotaspidini and Centridini species acting as specialized pollinators of Plantaginaceae suggest that there is a geographic variation in the pollinators of the same plant species, and that the evolutionary scenario of the historical relationships between oil-collecting bees and floral oil producing plants is more complex than previously considered.     

Pterandra pyroidea: a case of pollination shift within neotropical Malpighiaceae

Background and Aims

Most Neotropical species of Malpighiaceae produce floral fatty oils in calyx glands to attract pollinating oil-collecting bees, which depend on this resource for reproduction. This specialized type of pollination system tends to be lost in members of the family that occur outside the geographic distribution (e.g. Africa) of Neotropical oil-collecting bees. This study focused on the pollination ecology, chemical ecology and reproductive biology of an oil flower species, Pterandra pyroidea (Malpighiaceae) from the Brazilian Cerrado. Populations of this species consist of plants with oil-secreting (glandular) flowers, plants with non-oil-secreting flowers (eglandular) or a mix of both plant types. This study specifically aims to clarify the role of eglandular morphs in this species.

Methods

Data on pollinators were recorded by in situ observations. Breeding system experiments were conducted by isolating inflorescences and by enzymatic reactions. Floral resources, pollen and floral oils offered by this species were analysed by staining and a combination of various spectroscopic methods.

Key Results

Eglandular flowers of P. pyroidea do not act as mimics of their oil-producing conspecifics to attract pollinators. Instead, both oil-producing and oil-free flowers depend on pollen-collecting bees for reproduction, and their main pollinators are bumble-bees. Floral oils produced by glandular flowers are less complex than those described in closely related genera.

Conclusions

Eglandular flowers represent a shift in the pollination system in which oil is being lost and pollen is becoming the main reward of P. pyroidea flowers. Pollination shifts of this kind have hitherto not been demonstrated empirically within Neotropical Malpighiaceae and this species exhibits an unusual transition from a specialized towards a generalized pollination system in an area considered the hotspot of oil-collecting bee diversity in the Neotropics. Transitions of this type provide an opportunity to study ongoing evolutionary mechanisms that promote the persistence of species previously involved in specialized mutualistic relationships.     

The pollination of Krameria bahiana B.B. Simpson by bees in the Coastal Sand Plains of Bahia, Brazil

The flowers of K. bahiana mainly produce oil as floral resource for their visitors. Oil collecting bees usually show morphological and behavioral adaptation for their collection. This study focused on the analysis of interactions between the flowers of K. bahiana and their visiting bees, aiming for the efficiency of the pollination, in an area of the Coastal Sand Plains of Bahia State, Brazil. From February/2001 to February/2002 and from May to October/2002 observations were accomplished about the phenology and morphology of the plants and the floral visitors' behavior. The flowers of the inflorescences are zigomorphic, small sized, pink and present a pair of petals modified in epithelial elaiophores, which are responsible for the production of oil. These flowers were visited especially by bees of the genus Centris: C. leprieuri Spinola, C. tarsata Smith, C. trigonoides Lepeletier and C. pulchra Moure, Oliveira & Viana. The bees collected only oil in the flowers, by scratching the elaiophores and then transferring it to scopa located on the tibia and basitarsus of the hind legs. During those actions, the bees often contact the reproductive structures of the flowers, resulting in pollination. C. leprieuri was the most frequent bee during this study, thus considered the effective pollinator. Megachile dentipes Vachal also visited the flowers of K. bahiana, collecting only pollen. However, these bees were considered sporadic pollinators because they were not frequent in the flowers of K. bahiana in the months of observation.     

Low legitimate pollen flow in distylic Turnera hermannioides (Passifloraceae) and its consequences on fruit and seed set

Turnera hermannioides is a ruderal distylic subshrub, native to NE-Brazil. In the Catimbau National Park, situated within the semi-arid Caatinga region, we studied the pollination ecology of this species, emphasizing (1) effective pollinators; (2) characteristics of short- and long-styled flowers; (3) intra- and intermorph pollen flow; and (4) fruit and seed set. Short and long-styled morphs differ in pollen size and ornamentation, stigmatic surface, style and stamen length and nectar production. The flowers are obligate intermorphic outcrossers and depend on animals for pollination. The flowers of T. hermannioides attracted insect visitors of 25 species, among them butterflies, beetles, but mainly bees. Polylectic bees, such as Apis mellifera, stingless bees, and solitary Callonychium brasiliense were the most frequent visitors and the principal pollinators. The frequency of visits, however, was very low (on average 1.9 visits/flower/day), resulting in a low and unbalanced legitimate pollen flow, i.e. a much lower number of pollen grains from short-styled flowers reaching stigmas of long-styles than vice versa, which in turn compromised fruit and seed set. Surprisingly, Protomeliturga catimbaui and P. turnerae, both oligolectic on flowers of the Turneraceae-clade of the Passifloraceae s.l., were very rare flower visitors and did not contribute significantly to the pollination of Turnera hermannioides. We discuss how the low visitation rate and the inefficiency of pollinators (i.e. inefficiency in promoting legitimate pollination) compromise pollen flow and, consequently, fruit and seed set in this species.     

Mecardonia tenella (Plantaginaceae) Attracts Oil-, Perfume-, and Pollen-Gathering Bees in Southern Brazil

Floral characteristics often indicate the pollinators' functional group visiting the plant and the pollination syndromes associated with them. This idea has been challenged in the past decades due to increasing evidence that most plants, including those exhibiting floral syndromes, are visited by large arrays of species that differ in their effectiveness as pollinators. Our study focuses on Mecardonia tenella (Plantaginaceae) from the Araucaria forest of southern Brazil, which exhibits characteristics of the oil flower pollination syndrome. However, it is visited by three types of functional groups of bees: male orchid bees, oil-collecting bees, and pollen-seeking bees. The relative contribution of each functional group to the plant's reproductive success was estimated based on their pollen load, visitation frequency, and morphology. We assessed resources, phenology, and breeding system of M. tenella . Our results indicate that flowers lack nectar, but volatiles, lipids, and pollen are resources that can be gathered by visitors. This combination of floral traits and visitors' assemblage makes M. tenella a challenge to the concept of pollination syndromes. Our findings indicate that the current interactions may not reflect the circumstances under which some floral traits of this plant were selected.     

Notes on the pollination mechanisms ofMoraea inclinata andM. brevistyla (Iridaceae)

Individual flowers ofMoraea inclinata are nectariferous and last about six hours. They appear to be pollinated largely by bees in the familyHalictidae (Lasioglossum spp.,Nomia spp.,Zonalictus) and to a lesser extent by bees in the familyAnthophoridae (Amegilla). The mechanism of bee-pollination inM. inclinata is the Iris type; i.e., each flower consists of three pollination units (an outer tepal, a partly exserted anther, and the opposed style branch which terminates in a pair of petal-like crests). Bees rarely visit more than one pollination unit per flower. Transferral of pollen to the bee is passive and nototribic although all bees collected on the flowers were female and 55% of the bees carried pollen loads with 2–5 pollen taxa in their scopae.Moraea brevistyla flowers are nectariferous but lack scent and last two days. They are visited infrequently by bees and only one femaleLasioglossum spec. carried the pollen ofM. brevistyla. Unlike flowers ofM. inclinata those ofM. brevistyla deposit pollen only on the head and thorax. Bee-mediated autogamy in both species is avoided due to the erratic foraging patterns of the bees and the flexibility of each stigma lobe as the bee backs out of the flower. Approximately 2–4 flowers in the inflorescences of both species (6–8 flowers/infloresence) develop into capsules.     

Influence of brood, vent screening, and time of year on honey bee (Hymenoptera: Apidae) pollination and fruit quality of greenhouse tomatoes

Greenhouse tomatoes, Lycopersicon esculentum Miller (Solanaceae), are autogamous, but facilitated pollination results in increased fruit size and set. Previous research examining honey bee pollination in greenhouse tomato crops established that fruit quality resulting from honey bee visitation is often comparable to bumble bees (Bombus spp.) and significantly better than in flowers that receive no facilitated pollination. However, management alternatives have not been studied to improve tomato fruit quality when honey bees are the only pollination option available for the high-value greenhouse industry. We investigated whether the quantity of brood (eggs, larvae, and pupae) in a honey bee colony in the winter and screening on greenhouse vents in the summer would encourage honey bee foraging on tomato flowers. We also established the influence of time of year on the potential for honey bees to be effective pollinating agents. We constructed small honey bee colonies full of naive forager bees with either two frames of brood ("brood colonies") or two empty frames ("no-brood") and compared total fruit set and the number of tomato seeds resulting from fruit potentially visited by honey bees in each of these treatments to bagged flowers that received no facilitated pollination. There was no significant difference in the quality of fruit resulting from honey bees from "brood" and "no-brood" colonies. However, these fruits produced significantly more seeds than bagged flowers restricted from facilitated pollination. Honey bees from brood and no-brood colonies also resulted in 98% fruit set compared with 80% fruit set in bagged flowers that received no facilitated pollination. During the summer, the number of seeds per fruit did not differ significantly between unbagged flowers potentially visited by honey bees in screened greenhouses and unscreened greenhouses and bagged flowers that received no facilitated pollination. However, time of year did have a significant influence on the quality of fruit produced by honey bees compared with flowers that received no facilitated pollination, because no difference in seed number was observed between the treatments after mid-April. The results from this study demonstrate that the management of brood levels and vent screening cannot be used to improve the quality of fruit resulting from honey bee pollination and that honey bees can be a feasible greenhouse pollination alternative only during the winter.     

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.     

Breeding system and pollination by mimicry of the orchid Tolumnia guibertiana in Western Cuba

The mimicry of malpighiaceous oil‐flowers appears to be a recurrent pollination strategy among many orchids of the subtribe Oncidiinae. These two plant groups are mainly pollinated by oil‐gathering bees, which also specialize in pollen collection by buzzing. In the present study, the floral ecology of the rewardless orchid Tolumnia guibertiana (Oncidiinae) was studied for the first time. The orchid was self‐incompatible and completely dependent on oil‐gathering female bees (Centris poecila) for fruit production. This bee species was also the pollinator of two other yellow‐flowered plants in the area: the pollen and oil producing Stigmaphyllon diversifolium (Malpighiaceae) and the polliniferous and buzzing‐pollinated Ouratea agrophylla (Ochnaceae). To evaluate whether this system is a case of mimetism, we observed pollinator visits to flowers of the three plant species and compared the floral morphometrics of these flowers. The behavior, preferences and movement patterns of Centris bees among these plants, as well as the morphological data, suggest that, as previously thought, flowers of T. guibertiana mimic the Malpighiaceae S. diversifolium. However, orchid pollination in one of the studied populations appears to depend also on the presence of O. agrophylla. Moreover, at the two studied populations, male and female pollination successes of T. guibertiana were not affected by its own floral display, and did not differ between populations. The results are discussed in relation to the behavior and preferences of Centris bees, as well as the differential presence and influence of each of the two floral models.     

Inversostyly: a new stylar polymorphism in an oil-secreting plant, Hemimeris racemosa (Scrophulariaceae)

A new kind of stylar polymorphism, provisionally called inversostyly, is described. The polymorphism occurs in Hemimeris racemosa (Scrophulariaceae), a common annual herb of the Cape region of South Africa. Most populations are dimorphic for style orientation: the style alternates with the two stamens and is deflected either upwards or downwards. Thus, there is reciprocal placement of the style and stamens in a vertical plane in zygomorphic flowers. The flowers are symmetrical, and the floral parts do not vary in length. All flowers on a given plant are of the same stylar orientation. Pollination is by specialized oil-collecting bees (Rediviva spp.), which carry the pollen of the two morphs separately in discrete anterior or posterior locations on the underside of the body. Most inversostylous populations have a slightly higher proportion of the style-down morph, and this bias increases with decreasing pollinator abundance. In contrast with inversostylous populations, all individuals in homostylous populations of H. racemosa have the style and the stamens clustered together in the down position and high levels of autogamous seed set. Homostylous populations of H. racemosa, as well as the homostylous species Hemimeris sabulosa, occur where oil-collecting bees are less abundant.     

Pollen in Bee-Flower Relations Some Considerations on Melittophily*

Pollen and nectar are usually lumped together as floral rewards for pollinating bees, but they play totally different roles for flowers and bees (Table 1), as well as in the relationship between them. While flowers are specialized for certain pollinators via nectar, bees specialize on certain flowers via pollen. While flowers need pollen as a prerequisite for pollination, it is the essential larval food in bees. Thus, there is a strong competition between them for pollen. Foraging for pollen must be divided into three phases: uptake in the flower, reloading into and homeward transport within a carrying container. Bees have specializations for transport but hardly any for pollen uptake - and thus for pollination. Bees actively harvesting pollen usually do not pollinate. This only happens as a consequence of contamination of the bee by pollen. From these data a scenario is provided for the evolution of bees and bee flowers. Specialized bee flowers are often characterized by their ability to hide pollen from the bees and at the same time use them as optimal pollinators. If the relationship of bees and flowers is mutualistic at all it is best described as a balanced mutual exploitation.     

A Remarkable Case of Ornithophily in Calceolaria: Food Bodies as Rewards for a Non-nectarivorous Bird*

In southernmost South America, the pollination biology of Calceolaria uniflora Lam. (Scrophulariaceae) was studied in the field. One of the most striking features of the flower of this species is a corolla appendage folded against the outside of the lower lip. This massive and fleshy structure is pecked off by Thinocorus rumicivorus (Thinocoridae, Charadriiformes) as a food body. The percentage of damaged flowers averaged 64% and was as high as 81% in one study site. Pollen is placed on the front of the bird's head by the exserted stamens with large versatile anthers. This pollination syndrome is unique for the bird involved and exceptional in the kind of reward offered. This Calceolaria species, and probably a second one endemic to the Falkland Islands (Islas Malvinas), are the only ornithophilous species in a mostly oil-bee pollinated genus. Their reproduction strategy appears to be adapted to an environment lacking in oil-collecting bees.     

Specialized pollination by carpenter bees in Calanthe striata (Orchidaceae), with a review of carpenter bee pollination in orchids

Calanthe striata has nectarless flowers that are self‐compatible, but pollinator dependent. Field observations showed that the flowers were pollinated exclusively by the carpenter bee Xylocopa appendiculata circumvolans, although the bees occasionally wasted pollen by delivering to the stigmatic surface pollinaria that retained their anther caps. Fruit set ratios at the population level varied spatiotemporally, but were generally low (8.3–17.3%). Calanthe striata blooms in spring when post‐overwintering carpenter bees have not yet started foraging for brood production. It can therefore exploit an abundance of opportunistic/naïve foragers. This timing may also increase the possibility of pollinator visits, because no rewarding co‐flowering plants are available in the orchid habitats. A literature review of Orchidaceae pollinated by carpenter bees revealed that at least 14 species of Orchidoideae and Epidendroideae have evolved flowers specialized for carpenter bee pollination. They typically have shallow pink/magenta flowers with a foothold for pollinators; pollinaria are attached to the head, ventral thorax or base of the middle legs of carpenter bees when they insert their heads and/or proboscises into flowers; pollination success is generally low, a probable consequence of the deceptive pollination systems. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013 , 171 , 730–743.     

Twin oil sacs facilitate the evolution of a novel type of pollination unit (meranthium) in a South African orchid

The unique floral morphology of the South African orchid H. pulchra, with its twin meranthia, is best explained as an adaptation to pollination by oil-collecting bees. Flowers consisting of meranthia (floral parts that function as single pollination units; commonly observed in garden Iris) are extremely rare among the angiosperms and their significance poorly understood. Unlike all other known examples of meranthia, the novel type described for H. pulchra is not bilabiate. All Huttonaea species are unique in having twin petal sacs with glandular verrucae that secrete oil and are pollinated by Rediviva (Melittidae) oil-collecting bees. But only Huttonaea pulchra has long and widely divergent petal claws that place the oil sacs well beyond the reach of a centrally positioned bee. The wide separation of these sacs forces the pollinator, R. colorata, to visit each side of the flower independently and effectively divides the flower into two meranthia. Molecular data indicate that the evolution of the Huttonaea-type meranthium was dependent on the prior evolution of the oil flower/oil bee relationship. Meranthium evolution was also facilitated by the presence of oil in two separate structures (petal sacs) that were not physically constrained to remain in close proximity.     

The production of floral oils byMonttea (Scrophulariaceae) and the function of tarsal pads inCentris bees

Plant species that secrete oil as their primary floral reward are rare and sporadically found in the angiosperms. We report here thatMonttea, a genus previously unsuspected of being an oil-plant, produces lipids from trichome elaiophores on the inside of the lower (anterior) lip. The discovery of the production of oils by species of this S. American genus explains the occurrence of unusual dual-function collecting structures in ArgentineCentris (Hymenoptera: Anthophoridae) and explains the presence of oil-collecting bees in regions where oil-secreting flowers were previously thought to be absent. The behavior of these centridine pollinators onMonttea flowers parallels that of oil-collecting bees onDiascia (Scrophulariaceae) in S. Africa.     

Madagasikaria (Malpighiaceae): a new genus from Madagascar with implications for floral evolution in Malpighiaceae

Madagasikaria andersonii is described here as a new genus and species of Malpighiaceae from Madagascar. The phylogenetic placement of Madagasikaria was estimated by using combined data from ndhF and trnL-F chloroplast sequences and phytochrome (PHYC) and ITS nuclear sequences. It forms a strongly supported clade with the Malagasy endemic genera Rhynchophora and Microsteira. Despite nearly identical floral morphology among species in this clade (here called the madagasikarioid clade), these genera are easily distinguishable on the basis of their fruits. The schizocarpic fruits of Madagasikaria have distinctive mericarps. Each mericarp has a lateral wing, which completely encircles the nut, and a peculiar dorsal wing, which folds over on itself. The morphology of this fruit suggests that the homology of the unusual wing in Rhynchophora is lateral in nature and represents a reduced wing similar to the lateral wing in Madagasikaria. Taxa in the madagasikarioid clade all appear to be morphologically androdioecious and functionally dioecious, producing both staminate and "bisexual" (i.e., functionally carpellate) individuals. This condition appears to be exceedingly rare in flowering plants and has important implications for floral evolution within Malpighiaceae. Neotropical Malpighiaceae are pollinated by specialized oil-collecting anthophorine bees of the tribe Centridini and exhibit highly conserved floral morphology despite tremendous diversity in fruit morphology and habit. These oil-collecting bees are absent from the paleotropics, where most members of the Malpighiaceae lack both the oil glands and the typical floral orientation crucial to pollination by neotropical oil-collecting bees. The madagasikarioids represent one shift from the neotropical pollination syndrome among Old World Malpighiaceae.     

“金虎尾路线”植物的花进化与传粉转变

以金虎尾科植物地理分布格局及迁移历史总结出来的“金虎尾路线”, 是解释热带植物洲际间断分布与长距离扩散格局的重要模式。金虎尾路线阐明了金虎尾科植物历史时期7次独立的从起源中心(南美洲)向旧世界(非洲和亚洲)的洲际长距离扩散事件。本文总结了金虎尾路线植物起源地与扩散地主要类群的花部特征与传粉系统, 以探讨这些类群及类似植物长距离扩散后的花进化与传粉转变等适应规律。金虎尾科的南美洲类群都有分泌油脂的萼片腺体, 花的形态结构非常保守, 是与美洲当地特有的条蜂科集油蜂长期协同进化的结果。金虎尾科的非洲类群花保守性消失, 花白色、辐射对称且无萼片腺体, 繁育系统为雄花-两性花异株(功能性的雌雄异株), 传粉者是采集花粉的蜜蜂科昆虫。亚洲的一些属发生了类似非洲类群的泛化适应转变, 但风筝果属(Hiptage)出现了镜像花、异型雄蕊和极度反折的花瓣, 且传粉者是亚洲特有的大蜜蜂(Apis dorsata), 显示出了非常特化的适应性转变。风筝果属所在支系的现存类群涵盖了南美洲、中美洲、非洲和亚洲等地的地方特有属, 体现了金虎尾路线整个迁移历史过程, 是认识金虎尾路线及其进化适应规律的关键类群, 值得在今后的研究中加以重视。     

Flower color change accelerated by bee pollination in Tibouchina (Melastomataceae)

Floral color changes are common among Melastomataceae and have been interpreted as a warning mechanism for bees to avoid old flowers, albeit increasing long-distance flower display. Here the reproductive systems of Tibouchina pulchra and T. sellowiana were investigated by controlled pollinations. Their pollinators were identified, and experiments on floral color and fragrance changes were conduced to verify if those changes affect the floral visitation. Both Tibouchina species are self compatible. The flowers lasted three days or more, and the floral color changed from white in the 1st day to pink in the following days. Pollen deposition on stigma induced floral color change. The effectiveness of the pollination is dependent on bees’ size; only large bees were regarded as effective pollinators. In experimental tests, the bees in T. pulchra preferred the natural white flowers while the visitors of T. sellowiana were attracted by both natural and mimetic 1st-day flowers (2nd-day flowers with experimentally attached 1st-day flower petals). During the experiments on floral fragrance, the bees visited both natural and mimetic 1st-day flowers (2nd-day flowers with 1st-day flower scents). In both experiments, the bees avoided natural 2nd-day flowers, but seldom visited modified 2nd-day flowers. The attractiveness of T. pulchra and T. sellowiana flowers cannot be attributed exclusively to the color or the fragrance separately, both factors seemingly act together.     

Radiation of pollination systems in the Iridaceae of sub-Saharan Africa

BACKGROUND: Seventeen distinct pollination systems are known for genera of sub-Saharan African Iridaceae and recurrent shifts in pollination system have evolved in those with ten or more species. Pollination by long-tongued anthophorine bees foraging for nectar and coincidentally acquiring pollen on some part of their bodies is the inferred ancestral pollination strategy for most genera of the large subfamilies Iridoideae and Crocoideae and may be ancestral for the latter. Derived strategies include pollination by long-proboscid flies, large butterflies, night-flying hovering and settling moths, hopliine beetles and sunbirds. Bee pollination is diverse, with active pollen collection by female bees occurring in several genera, vibratile systems in a few and non-volatile oil as a reward in one species. Long-proboscid fly pollination, which is apparently restricted to southern Africa, includes four separate syndromes using different sets of flies and plant species in different parts of the subcontinent. Small numbers of species use bibionid flies, short-proboscid flies or wasps for their pollination; only about 2 % of species use multiple pollinators and can be described as generalists. SCOPE: Using pollination observations for 375 species and based on repeated patterns of floral attractants and rewards, we infer pollination mechanisms for an additional 610 species. Matching pollination system to phylogeny or what is known about species relationships based on shared derived features, we infer repeated shifts in pollination system in some genera, as frequently as one shift for every five or six species of southern African Babiana or Gladiolus. Specialized systems using pollinators of one pollination group, or even a single pollinator species are the rule in the family. Shifts in pollination system are more frequent in genera of Crocoideae that have bilaterally symmetric flowers and a perianth tube, features that promote adaptive radiation by facilitating precise shifts in pollen placement, in conjunction with changes in flower colour, scent and tube length. CONCLUSIONS: Diversity of pollination systems explains in part the huge species diversity of Iridaceae in sub-Saharan Africa, and permits species packing locally. Pollination shifts are, however, seen as playing a secondary role in speciation by promoting reproductive isolation in peripheral, ecologically distinct populations in areas of diverse topography, climate and soils. Pollination of Iridaceae in Eurasia and the New World, where the family is also well represented, is poorly studied but appears less diverse, although pollination by both pollen- and oil-collecting bees is frequent and bird pollination rare.