What shapes amino acid and sugar composition in Mediterranean floral nectars?

Petanidou, Theodora; Laere, André Van; Ellis, Willem N.; Smets, Erik

doi:10.1111/j.2006.0030-1299.14487.x

Cited by 146 publications

(170 citation statements)

References 53 publications

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“…Fine-scale spatial and temporal measurements, combined with floral and bud manipulations, revealed that elevated humidity levels are produced by evaporation and transpiration, two fundamental physical and physiological processes occurring naturally during anthesis. Nectar evaporation is a known source of postsecretory variation in nectar concentration and energetic content (22,23). Here we provide a proof of principle that elevated humidity levels produced by nectar evaporation could provide a condition-dependent indicator of profitability (in the presence of nectar, rather than its quality), to those flower-visiting animals capable of perceiving it.…”

Section: Discussionmentioning

confidence: 64%

Floral humidity as a reliable sensory cue for profitability assessment by nectar-foraging hawkmoths

Arx

Goyret

Davidowitz

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

118

148

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Most research on plant-pollinator communication has focused on sensory and behavioral responses to relatively static cues. Floral rewards such as nectar, however, are dynamic, and foraging animals will increase their energetic profit if they can make use of floral cues that more accurately indicate nectar availability. Here we document such a cue-transient humidity gradients-using the night blooming flowers of Oenothera cespitosa (Onagraceae). The headspace of newly opened flowers reaches levels of about 4% above ambient relative humidity due to additive evapotranspirational water loss through petals and water-saturated air from the nectar tube. Floral humidity plumes differ from ambient levels only during the first 30 min after anthesis (before nectar is depleted in wild populations), whereas other floral traits (scent, shape, and color) persist for 12-24 h. Manipulative experiments indicated that floral humidity gradients are mechanistically linked to nectar volume and therefore contain information about energy rewards to floral visitors. Behavioral assays with Hyles lineata (Sphingidae) and artificial flowers with appropriate humidity gradients suggest that these hawkmoth pollinators distinguish between subtle differences in relative humidity when other floral cues are held constant. Moths consistently approached and probed flowers with elevated humidity over those with ambient humidity levels. Because floral humidity gradients are largely produced by the evaporation of nectar itself, they represent condition-informative cues that facilitate remote sensing of floral profitability by discriminating foragers. In a xeric environment, this level of honest communication should be adaptive when plant reproductive success is pollinator limited, due to intense competition for the attention of a specialized pollinator.pollination biology | honest signaling | floral display P lant-pollinator relationships-like all mutualisms-strike a tenuous balance between the conflicting interests of foraging animals and flowering plants (1, 2). For flowering plants, pollinator attraction through floral density, form, color, pattern, and odor is necessary but insufficient to ensure effective pollination. Ideally, pollinators should transfer pollen between conspecific plants in ways that result in favorable levels of outcrossing (3) and reduced pollen loss (4). Flowers commonly manipulate pollinator movement by varying quality or quantity of floral nectar. The offer of variable amounts of nectar (5, 6), toxic nectar (7, 8), or an empty promise of nectar elicit similar results: pollinators leave plants sooner, reducing for example geitonogamous inbreeding (if selfcompatible) or pollen discounting (if self-incompatible).The availability of floral rewards often coincides with floral display and pollinator activity on a gross temporal scale (i.e., hours) (9, 10). Nevertheless, most pollinators encounter rewardless ("empty") flowers on a finer temporal scale (i.e., minutes), often due to recent visitation by another animal. From the pollin...

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Section: Discussionmentioning

confidence: 64%

Floral humidity as a reliable sensory cue for profitability assessment by nectar-foraging hawkmoths

Arx

Goyret

Davidowitz

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

118

148

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“…fructose) ratio of 0.16]. When compared with the results obtained for other closely related plant species, a low proportion of sucrose, resulting in hexose-rich or hexose-dominant nectars seems a common feature of Apiaceae (Percival 1961;Langenberger and Davis 2002;Petanidou et al 2006). This feature is also found in other plants with shallow, bowl-shaped flowers and exposed nectaries, and may be an adaptation to prevent the rapid evaporation of nectar (Corbet 1978;Vezza et al 2006).…”

Section: Discussionmentioning

confidence: 94%

Nectaries and male-biased nectar production in protandrous flowers of a perennial umbellifer Angelica sylvestris L. (Apiaceae)

2014

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Nectar is the most common floral pollinator reward. In dichogamous species, floral nectar production rates can differ between sexual phases. We studied the structure of nectaries located on the stylopodium and nectar production in protandrous umbellifer Angelica sylvestris. Our study species produced nectar in both floral sexual phases. Nectar sugar concentration was low (on average 22 ± 11 %, mean ± SD) and the nectar hexose rich and composed of sucrose, glucose, fructose and a small amount of amino acids, including b-alanine, a non-protein amino acid. Although nectar composition and sugar concentration varied little between floral sexual phases, nectar production showed a threefold reduction during the stigma receptive period. This is in contrast to other studies of Apiaceae that have reported female-biased nectar production, but in the direction predicted by plant sexual selection theory, suggesting that in pollen-unlimited species, floral rewards mainly enhance male reproductive success. The structure of the nectary was similar at the two sexual stages investigated, and composed of a secretory epidermis and several layers of nectariferous and subsecretory parenchyma. The nectary cells were small, had large nuclei, numerous small vacuoles and dense, intensely staining cytoplasm with abundant endoplasmic reticulum, mitochondria and secretory vesicles. They contained abundant resin-like material that may potentially act as defence against microbes. Starch was rarely observed in the nectary cells, occurring predominantly at the female stage and mainly in guard and parenchyma cells in close proximity to stomata, and in subsecretory parenchyma. The main route of nectar release in A. sylvestris seems to be via modified stomata.

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“…This expectation is not unreasonable, as the floral scents of populations of related plants often exhibit variation in subtle features such as differences in the concentration of the same odour compounds (Raguso et al 2003;, which result in small but perceivable differences (Wright et al , 2008. Furthermore, nectar rewards associated with floral scents also vary in quality (Petanidou et al 2006) and quantity (Herrera et al 2006) even in flowers produced by the same plant (Herrera et al 2006). Nectar is the currency of the interaction between plants and their pollinators: it costs plants to produce nectar ( Nepi & Stpiczynska 2008), and pollinators such as honeybees and bumblebees carefully attend to the nectar quality and to the probability of encountering food offered by flowers ( Waddington 2001;Cnaani et al 2006;Drezner-Levy & Shafir 2007;Shafir et al 2008).…”

Section: Introductionmentioning

confidence: 99%

Reward quality influences the development of learned olfactory biases in honeybees

2009

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Plants produce flowers with complex visual and olfactory signals, but we know relatively little about the way that signals such as floral scents have evolved. One important factor that may direct the evolution of floral signals is a pollinator's ability to learn. When animals learn to associate two similar signals with different outcomes, biases in their responses to new signals can be formed. Here, we investigated whether or not pollinators develop learned biases towards floral scents that depend on nectar reward quality by training restrained honeybees to learn to associate two similar odour signals with different outcomes using a classical conditioning assay. Honeybees developed learned biases towards odours as a result of differential conditioning, and the extent to which an olfactory bias could be produced depended upon the difference in the quality of the nectar rewards experienced during conditioning. Our results suggest that differences in reward quality offered by flowers influence odour recognition by pollinators, which in turn could influence the evolution of floral scents in natural populations of co-flowering plants.

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What shapes amino acid and sugar composition in Mediterranean floral nectars?

Cited by 146 publications

References 53 publications

Floral humidity as a reliable sensory cue for profitability assessment by nectar-foraging hawkmoths

Floral humidity as a reliable sensory cue for profitability assessment by nectar-foraging hawkmoths

Nectaries and male-biased nectar production in protandrous flowers of a perennial umbellifer Angelica sylvestris L. (Apiaceae)

Reward quality influences the development of learned olfactory biases in honeybees

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