Evolutionary associations between nectar properties and specificity in bird pollination systems.
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ABSTRACT:
SUBMITTER: Johnson SD
PROVIDER: S-EPMC2412932 | biostudies-literature | 2008 Feb
REPOSITORIES: biostudies-literature
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Evolutionary associations between nectar properties and specificity in bird pollination systems.
Johnson Steven D SD Nicolson Susan W SW
Biology letters 20080201 1
A long-standing paradigm in biology has been that hummingbirds and passerine birds select for different nectar properties in the plants they pollinate. Here we show that this dichotomy is false and a more useful distinction is that between specialized and generalized bird pollination systems. Flowers adapted for sunbirds, which are specialized passerine nectarivores, have nectar similar to that of hummingbird flowers in terms of volume (approx. 10-30 microl), concentration (approx. 15-25% w/w) a ...[more]
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Project description:BACKGROUND AND AIMS:The attractiveness of nectar rewards depends both on the quantity of nectar produced and on its chemical composition. It is known that nectar quantity and chemical composition can differ in plant species depending on the main pollinator associated with the species. The main aims of this study were to test formally whether nectar traits are adapted to pollination syndromes in the speciose Balsaminaceae and, if so, whether a combination of nectar traits mirrors pollination syndromes. METHODS:Comparative methods based on Ornstein-Uhlenbeck models were used to test whether nectar volume, nectar sucrose proportion, sugar and amino acid concentration and amino acid composition had evolved as a function of pollination syndromes in 57 species of Balsaminaceae. Cluster analysis and ordination were performed to derive clusters of species resembling each other in nectar composition. KEY RESULTS:Evolutionary models for nectar volume and nectar sucrose proportion performed best when including information on pollination syndrome, while including such information improve model fit neither for sugar and amino acid concentration nor for amino acid composition. A significant relationship emerged between pollination syndrome and the combined nectar traits. CONCLUSIONS:Our results show that nectar volume and nectar sucrose proportion evolve rapidly towards optimal values associated with different pollination syndromes. The detection of a signal indicating that nectar traits in combination are to a certain extent able to predict pollination syndromes in Balsaminaceae suggests that a holistic approach including the whole set of nectar traits helps us to better understand evolution of nectar composition in response to pollinators.
| S-EPMC6758581 | biostudies-literature
Project description:BackgroundInteractions with pollinators are proposed to be one of the major drivers of diversity in angiosperms. Specialised interactions with pollinators can lead to specialised floral traits, which collectively are known as a pollination syndrome. While it is thought that specialisation to a pollinator can lead to either an increase in diversity or in some cases a dead end, it is not well understood how transitions among specialised pollinators contribute to changes in diversity. Here, we use evolutionary trait reconstruction of bee-pollination and bird-pollination syndromes in Australian egg-and-bacon peas (Mirbelieae and Bossiaeeae) to test whether transitions between pollination syndromes is correlated with changes in species diversity. We also test for directionality in transitions that might be caused by selection by pollinators or by an evolutionary ratchet in which reversals to the original pollination syndrome are not possible.ResultsTrait reconstructions of Australian egg-and-bacon peas suggest that bee-pollination syndrome is the ancestral form and that there has been replicated evolution of bird-pollination syndromes. Reconstructions indicate potential reversals from bird- to bee-pollination syndromes but this is not consistent with morphology. Species diversity of bird-pollination syndrome clades is lower than that of their bee-pollination syndrome sisters.We estimated the earliest transitions from bee- to bird-pollination syndrome occurred between 30.8 Ma and 10.4 Ma. Geographical structuring of pollination syndromes was found; there were fewer bird-pollination species in the Australian southeast temperate region compared to other regions of Australia.ConclusionsA consistent decrease in diversification rate coincident with switches to bird pollination might be explained if greater dispersal by bird pollinators results in higher levels of connectivity among populations and reduced chances of allopatric speciation.The earliest transitions overlap with the early diversification of Australian honeyeaters - the major lineage of pollinating birds in Australia. Our findings are consistent with the idea that environment and availability of pollinators are important in the evolution of pollination syndromes. Changes in flower traits as a result of transitions to bird-pollination syndrome might also limit reversals to a bee-pollination syndrome.
| S-EPMC4015313 | biostudies-literature
Project description:BackgroundFloral nectar is an important determinant of plant-pollinator interactions and an integral component of pollination syndromes, suggesting it is under pollinator-mediated selection. However, compared to floral display traits, we know little about the evolutionary ecology of nectar. Combining a literature review with a meta-analysis approach, we summarize the evidence for heritable variation in nectar traits and link this variation to pollinator response and plant fitness. We further review associations between nectar traits and floral signals and discuss them in the context of honest signalling and targets of selection.ScopeAlthough nectar is strongly influenced by environmental factors, heritable variation in nectar production rate has been documented in several populations (mean h2 = 0.31). Almost nothing is known about heritability of other nectar traits, such as sugar and amino acid concentrations. Only a handful of studies have quantified selection on nectar traits, and few find statistically significant selection. Pollinator responses to nectar traits indicate they may drive selection, but studies tying pollinator preferences to plant fitness are lacking. So far, only one study conclusively identified pollinators as selective agents on a nectar trait, and the role of microbes, herbivores, nectar robbers and abiotic factors in nectar evolution is largely hypothetical. Finally, there is a trend for positive correlations among floral cues and nectar traits, indicating honest signalling of rewards.ConclusionsImportant progress can be made by studies that quantify current selection on nectar in natural populations, as well as experimental approaches that identify the target traits and selective agents involved. Signal-reward associations suggest that correlational selection may shape evolution of nectar traits, and studies exploring these more complex forms of natural selection are needed. Many questions about nectar evolution remain unanswered, making this a field ripe for future research.
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Project description:Specialization in plant pollination systems can arise from traits that function as filters of flower visitors. This may involve chemical traits such as floral volatiles that selectively attract favoured visitors and non-volatile nectar constituents that selectively deter disfavoured visitors through taste or longer-term toxic effects or both. We explored the functions of floral chemical traits in the African milkweed Gomphocarpus physocarpus, which is pollinated almost exclusively by vespid wasps, despite having nectar that is highly accessible to other insects such as honeybees. We demonstrated that the nectar of wasp-pollinated G. physocarpus contains cardenolides that had greater toxic effects on Apis mellifera honeybees than on Vespula germanica wasps, and also reduced feeding rates by honeybees. Behavioural experiments using natural compositions of nectar compounds showed that these interactions are mediated by non-volatile nectar chemistry. We also identified volatile compounds with acetic acid as a main component in the floral scent of G. physocarpus that elicited electrophysiological responses in wasp antennae. Mixtures of these compounds were behaviourally effective for attraction of V. germanica wasps. The results show the importance of both volatile and non-volatile chemical traits as filters that lead to specialization in plant pollination systems.
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Project description:This study establishes an altiudinal gradient, spanning from the highland Andes (2400 m) to lowland Amazon, as a productive region for the study of bird pollination in Southeastern Peru. The 'Manú Gradient' has a rich history of ornithological research, the published data and resources from which lay the groundwork for analyses of plant-bird interactions. In this preliminary expedition we documented 44 plants exhibting aspects of the bird pollination syndrome, and made field observations of hummingbird visits at three sites spanning the Manú Gradient: 2800 m (Wayqecha), 1400 m (San Pedro), and 400 m (Pantiacolla). Some of the documented plant taxa are underrepresented in the bird pollination literature and could be promising avenues for future analyses of their pollination biology. The Manú Gradient is currently the focus of a concerted, international effort to describe and study the birds in the region; we propose that this region of Southeastern Peru is a productive and perhaps underestimated system to gain insight into the ecology and evolution of bird pollination.Observations were made on 11, 19, and 14 putatively bird pollinated plant species found at the high-, mid- and low-elevation sites along the gradient, respectively. Hummingbirds visited 18 of these plant species, with some plant species being visited by multiple hummingbird species or the same hummingbird species on differing occasions. Morphometric data is presented for putatively bird-pollinated plants, along with bill measurements from hummingbirds captured at each of three sites. Voucher specimens from this study are deposited in the herbaria of the Universidad Nacional de Agraria de La Molina (MOL), Peru and the University of British Columbia (UBC), Canada. The specimens collected represent a 'snapshot' of the diversity of bird-pollinated flora as observed over 10 day sampling windows (per site) during the breeding season for hummingbirds of Manú .
| S-EPMC5904515 | biostudies-other
Project description:BACKGROUND AND AIMS:Floral colour is a primary signal in plant-pollinator interactions. The association between red flowers and bird pollination is well known, explained by the 'bee avoidance' and 'bird attraction' hypotheses. Nevertheless, the relative importance of these two hypotheses has rarely been investigated on a large scale, even in terms of colour perception per se. METHODS:We collected reflectance spectra for 130 red flower species from different continents and ascertained their pollination systems. The spectra were analysed using colour vision models for bees and (three types of) birds, to estimate colour perception by these pollinators. The differences in colour conspicuousness (chromatic and achromatic contrast, purity) and in spectral properties between pollination systems and across continents were analysed. KEY RESULTS:Compared with other floral colours, red flowers are very conspicuous to birds and much less conspicuous to bees. The red flowers pollinated by bees and by birds are more conspicuous to their respective pollinators. Compared with the bird flowers in the Old World, the New World ones are less conspicuous to bees and may be more conspicuous not only to violet-sensitive but also to ultraviolet-sensitive birds. These differences can be explained by the different properties of the secondary reflectance peak (SP). SP intensity is higher in red flowers pollinated by bees than those pollinated by birds (especially New World bird flowers). A transition from high SP to low SP in red flowers can induce chromatic contrast changes, with a greater effect on reducing attraction to bees than enhancing attraction to birds. CONCLUSIONS:Shades of red flowers differ between pollination systems. Moreover, red bird flowers are more specialized in the New World than in the Old World. The evolution towards colour specialization is more likely to result in higher efficiency of bee avoidance than bird attraction.
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Project description:BACKGROUND AND AIMS:Plant species that share pollinators are potentially subject to non-adaptive interspecific pollen transfer, resulting in reduced reproductive success. Mechanisms that increase pollination efficiency between conspecific individuals are therefore highly beneficial. Many nocturnally flowering plant species in Thailand are pollinated by the nectar bat Eonycteris spelaea (Pteropodidae). This study tested the hypothesis that plant species within a community reduce interspecific pollen movement by placing pollen on different areas of the bat's body. METHODS:Using flight cage trials, pollen transfer by E. spelaea was compared between conspecific versus heterospecific flowers across four bat-pollinated plant genera. Pollen from four locations on the bat's body was also quantified to determine if pollen placement varies by plant species. KEY RESULTS:It was found that E. spelaea transfers significantly more pollen between conspecific than heterospecific flowers, and that diverse floral designs produce significantly different patterns of pollen deposition on E. spelaea. CONCLUSIONS:In the Old World tropics, differential pollen placement is a mechanism that reduces competition among bat-pollinated plant species sharing a common pollinator.
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Project description:Bird pollination systems are diverse, ranging from narrow-tubed flowers pollinated by specialist nectarivores such as hummingbirds and sunbirds, to relatively open flowers pollinated by opportunistic (i.e. generalist) nectarivores. The role of opportunistic avian nectarivores as pollinators has historically been under-appreciated. A key aspect to understanding the importance of opportunistic birds as pollinators is to investigate how efficiently they transfer pollen among flowers. Here, we document the pollination and breeding systems of Schotia brachypetala, a southern African tree known as the 'weeping boer-bean' on account of its prolific production of dilute hexose-dominated nectar. The cup-shaped flowers of this tree attract a large number of bird species, including both opportunistic and specialist nectarivores. We identified floral visitors using observations and camera traps and quantified the floral traits responsible for animal attraction. We documented the breeding system, used selective pollinator exclusion to test the contribution of birds to fecundity, and performed supplemental pollination to test for pollen limitation. Single-visit pollen deposition trials were undertaken to determine the efficacy of bird pollinators. Controlled hand-pollination experiments showed that S. brachypetala is genetically self-incompatible and therefore dependent on pollinators for seed production. Supplemental hand-pollination experiments showed that natural fecundity is limited by either the amount and/or the quality of pollen on stigmas. Flowers from which birds but not insects were experimentally excluded set fewer seeds than open control flowers. Opportunistic birds deposited more pollen per visit than did specialist sunbirds. We conclude that S. brachypetala has a generalized bird pollination system that mainly involves opportunistic nectarivores.
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Project description:Nectar may contain many secondary metabolites that are commonly toxic and bitter-tasting. It has been hypothesized that such bitter-tasting secondary metabolites might keep the nectar exclusive to only a few pollinators. To test this hypothesis, we examined functional changes of bitter taste receptor genes (Tas2rs) in a species of nectar-feeding bird (Anna's hummingbird) by comparing these genes with those from two closely related insect-feeding species (chimney swift and chuck-will's widow). We previously identified a larger number of Tas2rs in the hummingbird than in its close insectivorous relatives. In the present study, we demonstrate higher sensitivity and new functions in the hummingbird Tas2r gene copies generated by a lineage-specific duplication, which has been shaped by positive selection. These results suggest that the bitter taste may lead to increased sensitivities and specialized abilities of the hummingbird to detect bitter-tasting nectar. Moreover, this study potentially supports the hypothesis that bitter-tasting nectar may have been specialized for some pollinators, thus enforcing plant-pollinator mutualism.
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Project description:The genus Viola is represented by four related species in Brazil belonging to section Leptidium, one of the most primitive sections in the genus. Floral biology and pollination by bees were studied in Viola cerasifolia and V. subdimidiata in high-altitude areas in south-eastern Brazil. Flowers are zygomorphic and spurred. The five stamens are arranged in a cuff around the ovary, and pollen is released by means of apical connective projections, which form a cone surrounding the base of the style. The connective projections of the inferior stamens are elongated and curved to form a hook-shaped structure. Nectar-secreting tissue can occur in the basal connective appendages of the inferior stamens, which project into the spur. Flowers of V. subdimidiata secreted a mean volume of 0.14 micro l nectar over a 24-h period; approx. 40 % of flowers did not secrete any nectar. The main pollinators of these Viola species are female bees belonging to the genus Anthrenoides (Andrenidae), which search mainly for pollen. These bees seem to be oligolectic and obtain large amounts of pollen from Viola by vibrating the flowers or by moving the hook repeatedly back and forth. Males of Anthrenoides patrol Viola clusters and also feed on nectar, acting as secondary pollinators. The basic floral structure in the genus Viola fits that of 'nectar flowers'. The uncommon hook-shaped projections, scanty nectar production, and behaviour of pollinators suggest that V. cerasifolia and V. subdimidiata are shifting their reward for pollinators from nectar to pollen. Based on floral morphology, this shift may be widespread in Viola sect. Leptidium.
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