Johnson S.D./Публикации

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Автор
АВТОР ПУБЛИКАЦИЙ 29
Hobbhahn N.
2
Автор антэкологических публикаций

et al. (+4)
Annals of Botany
514
Журнал с антэкологическими публикациями.
Oxford University Press · office@annbot.com

. 2013. V. 112. No. 7. P. 1303–1319. Статья
Background and AimsThe Orchidaceae have a history of recurring convergent evolution in floral function as nectar production has evolved repeatedly from an ancestral nectarless state. However, orchids exhibit considerable diversity in nectary type, position and morphology, indicating that this convergence arose from alternative adaptive solutions. Using the genus Disa, this study asks whether repeated evolution of floral nectaries involved recapitulation of the same nectary type or diversifying i
nnovation. Epidermis morphology of closely related nectar-producing and nectarless species is also compared in order to identify histological changes that accompanied the gain or loss of nectar production.MethodsThe micromorphology of nectaries and positionally equivalent tissues in nectarless species was examined with light and scanning electron microscopy. This information was subjected to phylogenetic analyses to reconstruct nectary evolution and compare characteristics of nectar-producing and nectarless species.Key ResultsTwo nectary types evolved in Disa. Nectar exudation by modified stomata in floral spurs evolved twice, whereas exudation by a secretory epidermis evolved six times in different perianth segments. The spur epidermis of nectarless species exhibited considerable micromorphological variation, including strongly textured surfaces and non-secreting stomata in some species. Epidermis morphology of nectar-producing species did not differ consistently from that of rewardless species at the magnifications used in this study, suggesting that transitions from rewardlessness to nectar production are not necessarily accompanied by visible morphological changes but only require sub-cellular modification.ConclusionsIndependent nectary evolution in Disa involved both repeated recapitulation of secretory epidermis, which is present in the sister genus Brownleea, and innovation of stomatal nectaries. These contrasting nectary types and positional diversity within types imply weak genetic, developmental or physiological constraints in ancestral, nectarless Disa. Such functional convergence generated by morphologically diverse solutions probably also underlies the extensive diversity of nectary types and positions in the Orchidaceae.
Scopece G.
2
Scopece G.
Автор антэкологических публикаций

et al. (+3)
The American Naturalist
6
Журнал с антэкологическими публикациями.
University of Chicago Press on behalf of the American Society of Naturalists · amnat@press.uchicago.edu

. 2010. V. 175. No. 1. P. 98–105. Статья
Abstract: The ultimate causes of evolution of highly specialized pollination systems are little understood. We investigated the relationship between specialization and pollination efficiency, defined as the proportion of pollinated flowers relative to those that experienced pollen removal, using orchids with different pollination strategies as a model system. Rewarding orchids showed the highest pollination efficiency. Sexually deceptive orchids had comparably high pollination efficiency, but fo
od‐deceptive orchids had significantly lower efficiency. Values for pollinator sharing (a measure of the degree of generalization in pollination systems) showed the reverse pattern, in that groups with high pollination efficiency had low values of pollinator sharing. Low pollinator sharing may thus be the basis for efficient pollination. Population genetic data indicated that both food‐ and sexually deceptive species have higher degrees of among‐population gene flow than do rewarding orchids. Thus, the shift from food to sexual deception may be driven by selection for more efficient pollination, without compromising the high levels of gene flow that are characteristic of deceptive species.
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Burger H.
1
Автор антэкологических публикаций

et al. (+3)
Flora
12
Журнал с антэкологическими публикациями.

. 2017. V. 232. P. 83–91. Статья
Floral traits may function as attractants for some flower visitors and also as mechanisms that filter out non-beneficial flower visitors. Our current understanding of floral filter mechanisms is limited as this particular aspect of floral function has received less attention than floral attractants. Here we report on a case of two closely related Gomphocarpus species, G. physocarpus and G. fruticosus, that are similar in their general floral shape and architecture but differ in their main pollin
ators, which are vespid wasps and honeybees, respectively. To identify the floral traits that best explain the observed pollinators we analysed and compared the floral scent composition, the flower colour, flower morphology, and nectar sugar composition of the two species. Furthermore, the response to floral scent was tested in behavioural experiments with Belanogaster and Polistes wasps. The floral scent composition differed significantly between the plant species. Acetic acid was a main component in the wasp-pollinated G. physocarpus, which is highly unusual for a floral scent bouquet. Choice experiments suggest that the species-specific odour might be responsible for the selective attraction of either wasps or bees. Furthermore, wasp-pollinated G. physocarpus flowers offer relatively large amounts of nectar that is freely accessible to insect visitors, whereas in G. fruticosus the site of nectar accumulation is covered by a specific morphological structure that makes it difficult for short-tongued insects such as wasps to access the nectar. Altogether, pollinator specialisation in the two Gomphocarpus species seem to be due to a combination of floral filter mechanisms and olfactory cues that cause flower visitors to learn to differentiate between the two species.
Johnson S.D.
31
Johnson S.D.
Автор антэкологических публикаций

, Bond W.J.
2
Bond W.J.
Автор антэкологических публикаций

Oecologia
330
Журнал с антэкологическими публикациями.
Springer

. 1992. V. 91. No. 3. P. 455–456. Статья
We examined the pollination success of Disa uniflora (Orchidaceae) in two habitats. Plants occurring in a rocky gorge were far more successful than plants occurring in an adjacent open valley. More than 55% of flowers in the gorge were pollinated and set fruit compared with less than 25% of flowers in the valley. These differences are explained by the preference of Meneris tulbaghia (Satyridae), the exclusive pollinator of the orchid, for rocky, sheltered habitats. Fruit set of hand-pollinated f
lowers did not differ significantly between the two habitats, indicating that resources did not account for the variation in fruiting success.
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Oecologia
330
Журнал с антэкологическими публикациями.
Springer

. 1997. V. 109. No. 4. P. 530–534. Статья
We used spot checks of stigmatic pollen deposition and hand-pollination experiments to test whether fruit production in Cape wildflower populations is limited by pollen availability. Natural levels of stigmatic pollen deposition were very low (median = 30.0% of flowers) in populations of 33 orchid species. We found similarly low levels of fruit set (median = 32% of flowers per plant) in six Orchidaceae and four Amaryllidaceae species. Experimental hand pollination at the whole plant level caused
significant increases in fruit production in 11 of the 12 study populations. These results indicate that pollen limitation of fruit set may occur frequently among some plant families in the Cape flora.
Annals of Botany
514
Журнал с антэкологическими публикациями.
Oxford University Press · office@annbot.com

. 2012. V. 109. No. 4. P. 761–772. Статья
Background and AimsPollen-collecting bees are among the most important pollinators globally, but are also the most common pollen thieves and can significantly reduce plant reproduction. The pollination efficiency of pollen collectors depends on the frequency of their visits to female(-phase) flowers, contact with stigmas and deposition of pollen of sufficient quantity and quality to fertilize ovules. Here we investigate the relative importance of these components, and the hypothesis that floral
and inflorescence characteristics mediate the pollination role of pollen collection by bees.MethodsFor ten Aloe species that differ extensively in floral and inflorescence traits, we experimentally excluded potential bird pollinators to quantify the contributions of insect visitors to pollen removal, pollen deposition and seed production. We measured corolla width and depth to determine nectar accessibility, and the phenology of anther dehiscence and stigma receptivity to quantify herkogamy and dichogamy. Further, we compiled all published bird-exclusion studies of aloes, and compared insect pollination success with floral morphology.Key ResultsSpecies varied from exclusively insect pollinated, to exclusively bird pollinated but subject to extensive pollen theft by insects. Nectar inaccessibility and strong dichogamy inhibited pollination by pollen-collecting bees by discouraging visits to female-phase (i.e. pollenless) flowers. For species with large inflorescences of pollen-rich flowers, pollen collectors successfully deposited pollen, but of such low quality (probably self-pollen) that they made almost no contribution to seed set. Indeed, considering all published bird-exclusion studies (17 species in total), insect pollination efficiency varied significantly with floral shape.ConclusionsSpecies-specific floral and inflorescence characteristics, especially nectar accessibility and dichogamy, control the efficiency of pollen-collecting bees as pollinators of aloes.
Vaughton G.
2
Автор антэкологических публикаций

, Ramsey M.
3
Автор антэкологических публикаций

, Johnson S.D.
30
Автор антэкологических публикаций

Annals of Botany
514
Журнал с антэкологическими публикациями.
Oxford University Press · office@annbot.com

. 2010. V. 106. No. 4. P. 547–555. Статья
Background and AimsAnimal 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.MethodsThe 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 ResultsNative 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.ConclusionsFlowers 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.
New Phytologist
33
Журнал с антэкологическими публикациями.
Wiley-Blackwell

. 2009. V. 183. No. 3. P. 530–545. Статья
Although not 'a professed botanist', Charles Darwin made seminal contributions to understanding of floral and inflorescence function while seeking evidence of adaptation by natural selection. This review considers the legacy of Darwin's ideas from three perspectives. First, we examine the process of floral and inflorescence adaptation by surveying studies of phenotypic selection, heritability and selection responses. Despite widespread phenotypic and genetic capacity for natural selection, only
one-third of estimates indicate phenotypic selection. Second, we evaluate experimental studies of floral and inflorescence function and find that they usually demonstrate that reproductive traits represent adaptations. Finally, we consider the role of adaptation in floral diversification. Despite different diversification modes (coevolution, divergent use of the same pollen vector, pollinator shifts), evidence of pollination ecotypes and phylogenetic patterns suggests that adaptation commonly contributes to floral diversity. Thus, this review reveals a contrast between the inconsistent occurrence of phenotypic selection and convincing experimental and comparative evidence that floral traits are adaptations. Rather than rejecting Darwin's hypotheses about floral evolution, this contrast suggests that the tempo of creative selection varies, with strong, consistent selection during episodes of diversification, but relatively weak and inconsistent selection during longer, 'normal' periods of relative phenotypic stasis.
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Annals of Botany
514
Журнал с антэкологическими публикациями.
Oxford University Press · office@annbot.com

. 2016. V. 117. No. 1. P. 25–36. Статья
Background and Aims Unrelated organisms that share similar niches often exhibit patterns of convergent evolution in functional traits. Based on bimodal distributions of hawkmoth tongue lengths and tubular white flowers in Africa, this study hypothesized that long-tongued hawkmoths comprise a pollination niche (ecological opportunity) that is distinct from that of shorter-tongued hawkmoths.Methods Field observations, light trapping, camera surveillance and pollen load analysis were used to identi
fy pollinators of plant species with very long-tubed (>8 cm) flowers. The nectar properties and spectral reflectance of these flowers were also measured. The frequency distributions of proboscis length for all captured hawkmoths and floral tube length for a representative sample of night-blooming plant species were determined. The geographical distributions of both native and introduced plant species with very long floral tubes were mapped.Key Results The convolvulus hawkmoth Agrius convolvuli is identified as the most important pollinator of African plants with very long-tubed flowers. Plants pollinated by this hawkmoth species tend to have a very long (approx. 10 cm) and narrow flower tube or spur, white flowers and large volumes of dilute nectar. It is estimated that >70 grassland and savanna plant species in Africa belong to the Agrius pollination guild. In South Africa, at least 23 native species have very long floral tubes, and pollination by A. convolvuli or, rarely, by the closely related hawkmoth Coelonia fulvinotata, has been confirmed for 11 of these species. The guild is strikingly absent from the species-rich Cape floral region and now includes at least four non-native invasive species with long-tubed flowers that are pre-adapted for pollination by A. convolvuli.Conclusions This study highlights the value of a niche perspective on pollination, which provides a framework for making predictions about the ecological importance of keystone pollinators, and for understanding patterns of convergent evolution and the role of floral traits in plant colonization.
Van der Niet T.
2
Автор антэкологических публикаций

et al. (+4)
Annals of Botany
514
Журнал с антэкологическими публикациями.
Oxford University Press · office@annbot.com

. 2014. V. 113. No. 2. P. 301–316. Статья
Background and AimsAccording to the Grant–Stebbins model of pollinator-driven divergence, plants that disperse beyond the range of their specialized pollinator may adapt to a new pollination system. Although this model provides a compelling explanation for pollination ecotype formation, few studies have directly tested its validity in nature. Here we investigate the distribution and pollination biology of several subspecies of the shrub Erica plukenetii from the Cape Floristic Region in South Af
rica. We analyse these data in a phylogenetic context and combine these results with information on pollinator ranges to test whether the evolution of pollination ecotypes is consistent with the Grant–Stebbins model.Methods and Key ResultsPollinator observations showed that the most common form of E. plukenetii with intermediate corolla length is pollinated by short-billed Orange-breasted sunbirds. Populations at the northern fringe of the distribution are characterized by long corollas, and are mainly pollinated by long-billed Malachite sunbirds. A population with short corollas in the centre of the range was mainly pollinated by insects, particularly short-tongued noctuid moths. Bird exclusion in this population did not have an effect on fruit set, while insect exclusion reduced fruit set. An analysis of floral scent across the range, using coupled gas chromatography–mass spectrometry, showed that the scent bouquets of flowers from moth-pollinated populations are characterized by a larger number of scent compounds and higher emission rates than those in bird-pollinated populations. This was also reflected in clear separation of moth- and bird-pollinated populations in a two-dimensional phenotype space based on non-metric multidimensional scaling analysis of scent data. Phylogenetic analyses of chloroplast and nuclear DNA sequences strongly supported monophyly of E. plukenetii, but not of all the subspecies. Reconstruction of ancestral character states suggests two shifts from traits associated with short-billed Orange-breasted sunbird pollination: one towards traits associated with moth pollination, and one towards traits associated with pollination by long-billed Malachite sunbirds. The latter shift coincided with the colonization of Namaqualand in which Orange-breasted sunbirds are absent.Conclusions Erica plukenetiiis characterized by three pollination ecotypes, but only the evolutionary transition from short- to long-billed sunbird pollination can be clearly explained by the Grant–Stebbins model. Corolla length is a key character for both ecotype transitions, while floral scent emission was important for the transition from bird to moth pollination.
В книге: Plant–pollinator interactions: from specialization to generalization / Editors: Waser N.M., Ollerton J. Chicago: The University of Chicago Press, 2006. 488 pp. AID: 5454444785. Book P. 283–307. AID: 5554877260. Часть книги
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Johnson S.D.
30
Автор антэкологических публикаций

, Jürgens A.
4
Автор антэкологических публикаций

, Kuhlmann M.
1
Автор антэкологических публикаций

Annals of Botany
514
Журнал с антэкологическими публикациями.
Oxford University Press · office@annbot.com

. 2012. V. 110. No. 3. P. 565–572. Статья
Background and AimsThe stigma, a structure which serves as a site for pollen receipt and germination, has been assumed to have evolved once, as a modification of carpels, in early angiosperms. Here it is shown that a functional stigma has evolved secondarily from modified tepals in some Albuca species (Hyacinthaceae).MethodsDeposition of pollen on Albuca floral organs by bees was recorded. Pollen germination and fruit set was measured in flowers that had pollen deposited solely on their tepals o
r had their tepal tips experimentally isolated or removed after pollination.Key ResultsLeafcutter bees deposit pollen onto the papillate apices of the inner tepals of Albuca flowers. Pollen germinates in tepal-derived fluid secreted 2 or 3 d after anthesis and pollen tubes subsequently penetrate the style during flower wilting. Application of cross-pollen to the inner tepal apices of A. setosa flowers led to high fruit set. No fruits were produced in pollinated flowers in which the inner tepals were mechanically isolated or removed.ConclusionsPollen capture by tepals in the Albuca clade probably evolved in response to selection for floral morphology that maximizes the accuracy of pollen transfer. These findings show how pollination function can be transferred among floral organs, and shed light on how the original angiosperm stigma developed from sporophylls.
Annals of Botany
514
Журнал с антэкологическими публикациями.
Oxford University Press · office@annbot.com

. 2011. V. 107. No. 6. P. 981–992. Статья
Background and AimsAlthough pollination of plants that attract flies by resembling their carrion brood and food sites has been reported in several angiosperm families, there has been very little work done on the level of specificity in carrion mimicry systems and the importance of plant cues in mediating such specialization. Specificity may be expected, as carrion-frequenting flies often exploit different niches, which has been interpreted as avoidance of interspecific competition. Interactions
between the orchid Satyrium pumilum and a local assemblage of carrion flies were investigated, and the functional significance of floral traits, especially scent, tested. Pollination success and the incidence of pollinator-mediated self-pollination were measured and these were compared with values for orchids with sexual- and food-deceptive pollination systems.Methods and Key ResultsObservations of insect visitation to animal carcasses and to flowers showed that the local assemblage of carrion flies was dominated by blow flies (Calliphoridae), house flies (Muscidae) and flesh flies (Sarcophagidae), but flowers of the orchid were pollinated exclusively by flesh flies, with a strong bias towards females that sometimes deposited live larvae on flowers. A trend towards similar partitioning of fly taxa was found in an experiment that tested the effect of large versus small carrion quantities on fly attraction. GC-MS analysis showed that floral scent is dominated by oligosulfides, 2-heptanone, p-cresol and indole, compounds that also dominate carrion scent. Flesh flies did not distinguish between floral and carrion scent in a choice experiment using olfactory cues only, which also showed that scent alone is responsible for fly attraction. Pollination success was relatively high (31·5 % of flowers), but tracking of stained pollinia also revealed that a relatively high percentage (46 %) of pollen deposited on stigmas originates from the same plant.ConclusionsSatyrium pumilum selectively attracts flesh flies, probably because its relatively weak scent resembles that of the small carrion on which these flies predominate. In this way, the plants exploit a specific subset of the insect assemblage associated with carrion. Pollination rates and levels of self-pollination were high compared with those in other deceptive orchids and it is therefore unlikely that this mimicry system evolved to promote outcrossing.
Kleizen C.
1
Kleizen C.
Автор антэкологических публикаций

, Midgley J.J.
6
Midgley J.J.
Автор антэкологических публикаций

, Johnson S.D.
31
Johnson S.D.
Автор антэкологических публикаций

Annals of Botany
514
Журнал с антэкологическими публикациями.
Oxford University Press · office@annbot.com

. 2008. V. 102. No. 5. P. 747–755. Статья
Background and Aims. Plants adapted for pollination by rodents tend to exhibit a distinct floral syndrome that includes dull coloured and geoflorous inflorescences and nocturnal anthesis and nectar production. On the basis of their floral traits, it was predicted that two African Colchicum species (C. scabromarginatum and C. coloratum) are rodent-pollinated. Methods. Field studies were carried out in the semi-arid Succulent Karoo region of South Africa. Live trapping of rodents was conducted and
pollen loads on the rodents were quantified. The daily periodicity of nectar production was determined. Selective exclusion and controlled pollination experiments were also conducted.

Key Results. Live-trapped rodents were found to carry large amounts of Colchicum pollen on the fur of their snouts, and in their faeces. Birds were occasional pollinators of flowers of C. coloratum. During the evening, nectar volume and concentration increased for both species. When vertebrates were excluded from C. scabromarginatum and C. coloratum plants, there was a significant decrease in seed set compared with open control plants. By contrast, vertebrate exclusion did not significantly affect seed production of a congener, C. hantamense, which has floral traits associated with insect pollination. Breeding system experiments revealed that both C. scabromarginatum and C. coloratum require pollinators for seed production. Colchicum scabromarginatum is strictly self-incompatible, whereas C. coloratum is partially self-compatible.

Conclusions. Pollination by rodents occurs in two African Colchicum species. C. scabromarginatum appears to depend exclusively on rodents for seed production, while birds and autonomous selfing may contribute to seed production in C. coloratum. These are the first records of rodent pollination in the Colchicaceae.
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Trends in Ecology and Evolution
20
Журнал с антэкологическими публикациями.
Cell Press · TREE@cell.com

. 2012. V. 27. No. 6. P. 353–361. Статья
Since Darwin,the diversity of flowers has been attributed to selection by pollinators. Although pollinators commonly act as selective agents on floral traits, determining the extent to which they have influenced angiosperm diversification requires a historical perspective. Here we review recent studies that combine species-level phylogenies withpollinatordata andshow that pollinator shifts are common, being associated with at least a quarter of documenteddivergence events. However, shiftfrequenc
y and directionality vary extensively, owing to variation in intrinsic factors such as floral features and phylogenetic history, as well as extrinsic factors such as interactions with local pollinator assemblages. Despite technical advances, phylogenies remain limited in their power to distinguish among various pollinator-driven evolutionary processes.
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Johnson S.D.
30
Автор антэкологических публикаций

, Ellis A.
1
Автор антэкологических публикаций

, Dötterl S.
4
Автор антэкологических публикаций

American Journal of Botany
146
Журнал с антэкологическими публикациями.
Botanical Society of America · ajb@botany.org

. 2007. V. 94. No. 1. P. 47–55. Статья
Next Section Abstract Exposed nectar presentation is a key trait in flowers specialized for pollination by short-tongued insects. We investigated the pollination of Satyrium microrrhynchum, a rare South African orchid in which nectar is secreted as droplets on long floral hairs (“lollipop hairs”) at the mouth of a shallow labellum. Our observations indicate that this orchid is pollinated specifically by two insect species: a cetoniid beetle (Atrichelaphinus tigrina) and a pompilid wasp (Hemipeps
is hilaris). Both insects have short mouthparts and remove nectar from the hairs with sweeping motions of their mouthparts. Pollinaria become attached to the upper surface of their heads while they feed on the nectar. Beetles damage the hairs while feeding, which may explain the positive relationship between hair damage and pollination success in plants of S. microrrhynchum from populations where beetles were common. The orchid has cryptic green-yellow flowers with spectral reflectance similar to that of its leaves. The fragrance from plants in three populations, analyzed using gas chromatography coupled to mass spectrometry, was dominated by various terpenoids; linalool was the most abundant. Plants in different populations emitted similar compounds, but eugenol and derivatives of this compound were found in only one of the three populations. In an electrophysiological study (gas chromatography coupled to electroantennography), using antennae of A. tigrina, clear signals were elicited by some of the floral scent compounds.
Plant Systematics and Evolution
49
Журнал с антэкологическими публикациями.
Springer Science+Business Media

. 2012. V. 298. No. 5. P. 857–869. Статья
Most lineages in the African genus Protea consist of species with large unscented flowers pollinated principally by birds, and several of these lineages also show evidence of shifts to rodent pollination, associated with concealed yeasty-scented flowerheads. In this study we investigated the hypothesis that brightly coloured and fruity-scented flowerheads of four Protea species (P. caffra, P. simplex, P. dracomontana and P. welwitschii) represent a novel shift from bird to insect pollination in
a grassland lineage in the genus. These species are visited by a wide range of insects, but cetoniine beetles were found to be the most important pollinators because of their abundance, size and relatively pure pollen loads. Three of the four putatively insect-pollinated Protea species have flowers presented at ground level, and experiments showed that cetoniine beetles preferred inflorescences at ground level to those artificially elevated to the height of shrubs and small trees. Relative to insects, birds were infrequent visitors to all of the study species. The nectar of all the study species contained xylose, as documented previously in bird- and rodent-pollinated Protea species, suggesting that this is a phylogenetically conserved trait. However, the very low concentration of nectar (ca. 8%), short nectar-stigma distance and the fruity scent of florets appear to be traits that are associated with specialisation for pollination by cetoniine beetles.
Annals of Botany
514
Журнал с антэкологическими публикациями.
Oxford University Press · office@annbot.com

. 2014. V. 113. No. 2. P. 277–288. Статья
Background and AimsFloral diversification driven by shifts between pollinators has been one of the key explanations for the radiation of angiosperms. According to the Grant–Stebbins model of pollinator-driven speciation, these shifts result in morphologically distinct ‘ecotypes’ which may eventually become recognizable as species. The current circumscription of the food-deceptive southern African orchid Eulophia parviflora encompasses a highly variable monophyletic species complex. In this study
, two forms were identified within this complex that differ in distribution, floral morphology, scent chemistry and phenology, and a test was made of whether these differences represent adaptations for different pollinators.Methods and ResultsMultivariate analysis of floral and vegetative traits revealed that there are at least two discrete morphological forms in the species complex. Field observations revealed that each form is pollinated by a different insect species, and thus represent distinct ecotypes. The early-flowering coastal form which has long spurs and floral scent dominated by sesquiterpene compounds is pollinated exclusively by the long-tongued bee Amegilla fallax (Apidae, Anthophorinae), while the late-flowering inland form with short spurs and floral scent dominated by benzenoid compounds is pollinated exclusively by the beetle Cyrtothyrea marginalis (Cetoniinae; Scarabaeidae). Choice experiments in a Y-maze olfactometer showed that beetles are preferentially attracted to the scent of the short-spurred form. A spur-shortening experiment showed that long spurs are required for effective pollination of the bee-pollinated form. Although it was initially thought likely that divergence occurred across a geographical pollinator gradient, plants of the long-spurred form were effectively pollinated when transplanted to an inland locality outside the natural coastal range of this form. Thus, the underlying geographical basis for the evolution of ecotypes in the E. parviflora complex remains uncertain, although early flowering in the long-spurred form to exploit the emergence of naïve bees may restrict this form to coastal areas where there is no frost that would damage flower buds. Later flowering of the short-spurred form coincides closely with the emergence of the pollinating beetles following winter frosts.ConclusionsThis study identifies a shift between bee and beetle pollination as the main driver of floral divergence in an orchid species complex. Floral scent and spur length appear to be key traits in mediating this evolutionary transition.
American Journal of Botany
146
Журнал с антэкологическими публикациями.
Botanical Society of America · ajb@botany.org

. 2001. V. 88. No. 10. P. 1768–1773. Статья
Field studies in the semiarid Succulent Karoo region of South Africa showed that flowers of Massonia depressa (Hyacinthaceae) are visited at night by at least four rodent species, including two gerbil species. Live-trapped rodents were found to carry Massonia pollen on their snouts; they also had large quantities of Massonia pollen in their feces as a result of grooming their fur. Visits by insects to the flowers were infrequent at one site and apparently absent at another site. Plants enclosed
in large-mesh wire cages, which excluded rodents but not insects, set very few seeds relative to open controls. Our initial hypothesis of rodent-pollination in M. depressa was based on the striking similarity of its flowers to those of unrelated, rodent-pollinated Protea species. Convergent traits include dull-colored and very robust flowers situated at ground level, a strong yeasty odor, and secretion of copious amounts of sucrose-dominant nectar during the evening when rodents are active. Despite having a low sugar concentration (∼20%), the nectar of M. depressa is almost 400 times as viscous as an equivalent sugar solution. The jelly-like constituent in the nectar may discourage robbing by insects, while also facilitating lapping by rodents. Our findings illustrate the utility of floral syndromes for generating testable predictions about pollination systems.
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Patrick K.L.
1
Автор антэкологических публикаций

, Johnson S.D.
30
Автор антэкологических публикаций

, Duffy K.J.
1
Автор антэкологических публикаций

Plant Biology
4
Журнал с антэкологическими публикациями.

. 2018. V. 20. No. 4. P. 780–788. Статья
Plant species that are effective colonizers of transient habitats are expected to have a capacity for uniparental reproduction and show flexibility in pollination systems. Such traits may enable populations to be established from a small number of founding individuals without these populations succumbing to reductions in fecundity arising from pollinator limitation. We tested these predictions for Aloe thraskii (Xanthorrhoeaceae), a succulent treelet that colonizes shifting coastal dunes and has
both bird and bee pollinators. We performed hand pollination experiments, and selectively excluded bird visitors to determine differences in pollinator effectiveness. We measured pollinator visitation rates and fecundity in populations varying in their size, density, and isolation distance. Controlled hand pollinations revealed that unlike most other Aloe species, A. thraskii is self-compatible and thus capable of uniparental reproduction. The species does however depend on pollinators and is visited by various bird species as well as by bees. Fruit and seed set are not affected by selective exclusion of birds, thus indicating that bees are effective pollinators. Bird visitation rates increased with increasing plant height and population size, while bee visitation rates increased with increasing population size and density. We found that seed set per flower was lower in large populations than in small populations. These results suggest that establishment of populations of A. thraskii from a small number of individuals is unlikely to be limited by the fecundity of individual plants.
Hobbhahn N.
2
Автор антэкологических публикаций

et al. (+4)
Plant Biology
4
Журнал с антэкологическими публикациями.

. 2017. V. 19. No. 5. P. 775–786. Статья
Unrelated plants adapted to particular pollinator types tend to exhibit convergent evolution in floral traits. However, inferences about likely pollinators from “pollination syndromes” can be problematic due to trait overlap among some syndromes and unusual floral architecture in some lineages. An example is the rare South African parasitic plant Mystropetalon thomii (Mystropetalaceae), which has highly unusual brush-like inflorescences that exhibit features of both bird- and rodent-pollination
syndromes.

We used camera traps to record flower visitors, quantified floral spectral reflectance and nectar and scent production, experimentally determined self-compatibility and breeding system, and studied pollen dispersal using fluorescent dyes.

The dark-red inflorescences are usually monoecious, with female flowers maturing before male flowers, but some inflorescences are purely female (gynoecious). Inflorescences were visited intensively by several rodent species that carried large pollen loads, while visits by birds were extremely rare. Rodents prefer male- over female-phase inflorescences, likely because of the male flowers’ higher nectar and scent production. The floral scent contains several compounds known to attract rodents. Despite the obvious pollen transfer by rodents, we found that flowers on both monoecious and gynoecious inflorescences readily set seed in the absence of rodents and even when all flower visitors are excluded. Our findings suggest that seed production occurs at least partially through apomixis and that M. thomii is not ecologically dependent on its rodent pollinators. Our study adds another species and family to the growing list of rodent-pollinated plants, thus contributing to our understanding of the floral traits associated with pollination by non-flying mammals.
Hargreaves A.L.
4
Автор антэкологических публикаций

, Johnson S.D.
30
Автор антэкологических публикаций

, Nol E.
1
Автор антэкологических публикаций

Oecologia
330
Журнал с антэкологическими публикациями.
Springer

. 2004. V. 140. No. 2. P. 295–301. Статья
We investigated whether the “ornithophilous” floral syndrome exhibited in an African sugarbush, Protea roupelliae (Proteaceae), reflects ecological specialization for bird-pollination. A breeding system experiment established that the species is self-compatible, but dependent on visits by pollinators for seed set. The cup-shaped inflorescences were visited by a wide range of insect and bird species; however inflorescences from which birds, but not insects, were excluded by wire cages set few se
eds relative to open-pollinated controls. One species, the malachite sunbird (Nectarinia famosa), accounted for more than 80% of all birds captured in P. roupelliae stands and carried the largest protea pollen loads. A single visit by this sunbird species was enough to increase seed set considerably over unvisited, bagged inflorescences. Our results show that P. roupelliae is largely dependent on birds for pollination, and thus confirm the utility of floral syndromes for generating hypotheses about the ecology of pollination systems.
Annals of Botany
514
Журнал с антэкологическими публикациями.
Oxford University Press · office@annbot.com

. 2018. V. 123. No. 2. P. 311–325. Статья
Background and Aims. Large clades of angiosperms are often characterized by diverse interactions with pollinators, but how these pollination systems are structured phylogenetically and biogeographically is still uncertain for most families. Apocynaceae is a clade of >5300 species with a worldwide distribution. A database representing >10 % of species in the family was used to explore the diversity of pollinators and evolutionary shifts in pollination systems across major clades and regions.
Methods. The database was compiled from published and unpublished reports. Plants were categorized into broad pollination systems and then subdivided to include bimodal systems. These were mapped against the five major divisions of the family, and against the smaller clades. Finally, pollination systems were mapped onto a phylogenetic reconstruction that included those species for which sequence data are available, and transition rates between pollination systems were calculated. Key Results. Most Apocynaceae are insect pollinated with few records of bird pollination. Almost three-quarters of species are pollinated by a single higher taxon (e.g. flies or moths); 7 % have bimodal pollination systems, whilst the remaining approx. 20 % are insect generalists. The less phenotypically specialized flowers of the Rauvolfioids are pollinated by a more restricted set of pollinators than are more complex flowers within the Apocynoids + Periplocoideae + Secamonoideae + Asclepiadoideae (APSA) clade. Certain combinations of bimodal pollination systems are more common than others. Some pollination systems are missing from particular regions, whilst others are over-represented. Conclusions. Within Apocynaceae, interactions with pollinators are highly structured both phylogenetically and biogeographically. Variation in transition rates between pollination systems suggest constraints on their evolution, whereas regional differences point to environmental effects such as filtering of certain pollinators from habitats. This is the most extensive analysis of its type so far attempted and gives important insights into the diversity and evolution of pollination systems in large clades.
Trends in Ecology and Evolution
20
Журнал с антэкологическими публикациями.
Cell Press · TREE@cell.com

. 2000. V. 15. No. 4. P. 140–143. Статья
The long-standing notion that most angiosperm flowers are specialized for pollination by particular animal types, such as birds or bees, has been challenged recently on the basis of apparent widespread generalization in pollination systems. At the same time, biologists working mainly in the tropics and the species-rich temperate floras of the Southern hemisphere are documenting pollination systems that are remarkably specialized, often involving a single pollinator species. Current studies are a
imed at understanding: (1) the ecological forces that have favoured either generalization or specialization in particular lineages and regions; (2) the implications for selection on floral traits and divergence of populations; and (3) the risk of collapse in plant–pollinator mutualisms of varying specificity.
Annals of Botany
514
Журнал с антэкологическими публикациями.
Oxford University Press · office@annbot.com

. 2003. V. 92. No. 6. P. 807–834. Статья
The KwaZulu‐Natal region of South Africa hosts a large diversity of asclepiads (Apocynaceae: Asclepiadoideae), many of which are endemic to the area. The asclepiads are of particular interest because of their characteristically highly evolved floral morphology. During 3 months of fieldwork (November 2000 to January 2001) the flower visitors and pollinators to an assemblage of nine asclepiads at an upland grassland site were studied. These observations were augmented by laboratory studies of flow
er morphology (including scanning electron microscopy) and flower colour (using a spectrometer). Two of the specialized pollination systems that were documented are new to the asclepiads: fruit chafer pollination and pompilid wasp pollination. The latter is almost unique in the angiosperms. Taxa possessing these specific pollination systems cluster together in multidimensional phenotype space, suggesting that there has been convergent evolution in response to similar selection to attract identical pollinators. Pollination niche breadth varied from the very specialized species, with only one pollinator, to the more generalized, with up to ten pollinators. Pollinator sharing by the specialized taxa does not appear to have resulted in niche differentiation in terms of the temporal or spatial dimensions, or with regards to placement of pollinaria. Nestedness analysis of the data set showed that there was predictability and structure to the pattern of plant‐pollinator interactions, with generalist insects visiting specialized plants and vice versa. The research has shown that there is still much to be learned about plant–pollinator interactions in areas of high plant diversity such as South Africa.
American Journal of Botany
146
Журнал с антэкологическими публикациями.
Botanical Society of America · ajb@botany.org

. 2007. V. 94. No. 4. P. 650–659. Статья
Next Section Abstract The African orchid flora has a high proportion of species with long-spurred white flowers. Few data exist to test the prediction that this floral syndrome pattern reflects an important role for hawkmoth pollination in the evolution and ecology of these orchids. The pollination biology of five aerangoid orchid species (Rangaeris amaniensis, Aerangis brachycarpa, A. confusa, A. thomsonii, and A. kotschyana) was investigated in Kenya. Four of these have long spurs (>10 cm) and
were pollinated by Agrius convolvuli and Coelonia fulvinotata. Aerangis confusa, which has relatively short spurs (ca. 4 cm), was pollinated by the short-tongued hawkmoths Hippotion celerio and Daphnis nerii. Nectar frequently filled the entire spur in some of the study species, even at anthesis. Sugar concentration of the nectar of four species was found to vary from ca. 1% at the mouth of the spur to 20% at the tip. Gradients were expressed more strongly in species with long, straight spurs. Species with spirally twisted spurs showed both steep and shallow nectar gradients. These gradients, previously unknown in plants, may function as a “sugar trail,” enticing long-tongued hawkmoths to probe deeply into spurs without incurring the cost of filling an entire spur with concentrated nectar. In addition, the most concentrated nectar is kept out of reach of short-tongued pollinators.
Trends in Ecology and Evolution
20
Журнал с антэкологическими публикациями.
Cell Press · TREE@cell.com

. 2000. V. 15. No. 4. P. 140–143. Статья
The long-standing notion that most angiosperm flowers are specialized for pollination by particular animal types, such as birds or bees, has been challenged recently on the basis of apparent widespread generalization in pollination systems. At the same time, biologists working mainly in the tropics and the species-rich temperate floras of the Southern hemisphere are documenting pollination systems that are remarkably specialized, often involving a single pollinator species. Current studies are a
imed at understanding: (1) the ecological forces that have favoured either generalization or specialization in particular lineages and regions; (2) the implications for selection on floral traits and divergence of populations; and (3) the risk of collapse in plant–pollinator mutualisms of varying specificity.
American Journal of Botany
146
Журнал с антэкологическими публикациями.
Botanical Society of America · ajb@botany.org

. 2012. V. 99. No. 6. P. 1104–1111. Статья
• Premise of the study: A useful, but seldom applied, measure of the effectiveness of different pollinators is their contribution to the rate of outcrossing. This measure is particularly useful in facultatively autogamous plants for which seed set cannot be used as a direct measure of pollinator effectiveness. We used selective exclusion experiments to assess the importance of insects for outcrossing in Protea caffra, a facultatively autogamous shrub with scented flowers that are visited frequen
tly by both birds and insects (mainly beetles).

• Methods and results: Pollen loads on stigmas, pollen tube growth, seed set, seed mass, germination, and early seedling survivorship were similar for vertebrate‐excluded and open‐pollinated inflorescences. Pollen‐supplementation mostly did not increase seed set, revealing resource limitation. Mean multilocus outcrossing rates, estimated using eight polymorphic allozyme loci, were similar for progeny from inflorescences excluded from bird visitors (0.65) and for those visited by both birds and insects (0.59). Wright's fixation indices indicated that the adult population is near Hardy–Weinberg equilibrium but differed markedly for maternal plants (FIS = –0.187 ± 0.065) and their early stage progeny (FIS = 0.258 ± 0.002). Since seed from self and cross hand‐pollinations were equally viable in terms of germination, this discrepancy in FIS could be explained by inbreeding depression that occurs between germination and reproductive maturity.

• Conclusions: Since outcrossing rates were not reduced when birds were excluded, we infer that insects are effective agents of cross pollination in P. caffra. This helps to explain the evolution of traits associated with insect pollination, such as fruity floral scent, in this species.
Peter C.I.
4
Peter C.I.
Автор антэкологических публикаций

, Johnson S.D.
31
Johnson S.D.
Автор антэкологических публикаций

Annals of Botany
514
Журнал с антэкологическими публикациями.
Oxford University Press · office@annbot.com

. 2006. V. 97. No. 3. P. 345–355. Статья
Background and Aims. 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 a
ppears to prevent self-pollination in the South African orchid Eulophia foliosa is examined.

Methods. 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. Key Results. 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.

Conclusions. 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.
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