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Mean relative values (+s.e.) of odour compounds identified in headspace samples of Anacamptis coriophora
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A comparative investigation was made of floral scent variation in the closely related, food-rewarding Anacamptis coriophora and the food-deceptive Anacamptis morio in order to identify patterns of variability of odour compounds in the two species and their role in pollinator attraction/avoidance learning.
Scent was collected from plants in natural...
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The Australian orchid genus Caladenia is unusual in comprising species that have evolved different pollination syndromes, including food deception and sexual deception. In this study, we compare the scent emission of Caladenia longicauda Lindl. (food deceptive), Caladenia arenicola Hopper & A. P. Br. (sexually deceptive), and their putative F1 hybr...
We report the chemical composition of the floral rewards and the fragrance of 10 Maxillariinae (Orchidaceae) species. The species that offer rewards (labellar secretions) are usually scentless, the rewards being collected by bees. Chemical analyses revealed that the major chemical class of compounds present in the labellar secretions are triterpeno...
Citations
... Thus, in these pollination strategies, pollinator-mediated natural selection is not expected to eliminate floral variation, potentially leading to high intraspecific flower polymorphisms. Accordingly, higher rates of intraspecific phenotypic variability in deceptive orchid species compared to rewarding ones have been reported (Heinrich 1975;Salzmann et al. 2007;Ackerman et al. 2011). The traditional hypothesis to explain this elevated phenotypic polymorphism in deceptive species is that it would slow down pollinator avoidance learning ability thus increasing plant reproductive success (Heinrich 1975;Nilsson 1992;Smithson & Macnair 1997;Ferdy et al. 1998). ...
Deceptive plants often exhibit elevated levels of polymorphism. The basis of the association between flower polymorphism and deceptive strategies, however, remains unclear. Epidendrum fulgens , a Neotropical deceptive orchid pollinated by butterflies, has an unexplored intrapopulation flower colour polymorphism. Here, we investigate the consequences of this polymorphism on its reproductive success.
We performed field and common garden experiments, aiming to detect pollinator‐mediated selection strength and direction over time, and test whether the presence of multiple colour morphs increases species' reproductive success. In the field, we monitored plant reproductive success and floral morphology on two populations over two flowering seasons and performed selection gradient analyses. In the common garden, we assembled plots of cultivated plants with same and different flower colour individuals (i.e., mono‐ and polymorphic plots), exposed them to pollinators and monitored their reproductive success. In both sites we also monitored the local pollinator community.
In the field, colour morphs performed equally, but we found coherences between morphological differentiation and the direction of selection, which was very dynamic. In the common garden, mono‐ and polymorphic plots also performed equally, with highly variable reproductive success over time. We also found a highly diverse pollinator community.
Our results suggest that flower polymorphism in E. fulgens is maintained by a combination of factors, including varying pollinator‐mediated selection, assortative mating due to differential pollinator preferences and different phenotype heritability. Natural selection varied across time and space, indicating a dynamic interplay between pollinators and flower morphs.
... For instance, Wright et al. (2008) found that honeybees reject scent-modi ed owers even if they contain familiar scent compounds, highlighting the importance of scent consistency for pollinator recognition. Many rewardless owers emit weak or highly variable scent, likely to avoid detection by scent-learning pollinators (Jersáková and Johnson, 2006;Salzmann et al., 2007). Salzmann et al. (2007) found that rewarding orchids produce strong, consistent scents that bees can detect, whereas deceptive orchids emit weak, highly variable scents. ...
... Many rewardless owers emit weak or highly variable scent, likely to avoid detection by scent-learning pollinators (Jersáková and Johnson, 2006;Salzmann et al., 2007). Salzmann et al. (2007) found that rewarding orchids produce strong, consistent scents that bees can detect, whereas deceptive orchids emit weak, highly variable scents. Similarly, oral compounds that attract pollinators tend to be more consistent across populations and species, while non-attractive compounds show greater variability (Mant et al., 2005;Huber et al., 2005). ...
To attract pollinators, flowering plants evolve diverse sensory traits into compelling signals. Floral scent, in particular, plays a key role in drawing bees from a distance and shaping their foraging choices. Scent composition varies widely, including across flowers of the same plant species. Yet, it is unclear whether scent variability influences bee flower choices, and thus whether plants would be under selection to minimise variation in their scent composition. Since bees typically avoid variability in rewards, we hypothesised they would favour flowers with more consistent scents. To test this, we trained individual bumblebees ( Bombus terrestris ) on two equally rewarding flower arrays: one with a consistent scent blend across flowers, and the other with variable scent blends between flowers. Contrary to expectations, bees showed no preference for scent consistency. They readily foraged from both arrays across bouts and did not favour either flower type in the binary choice test. To the best of our knowledge, this is the first study to examine how bees respond to scent variability. A better understanding of scent profile preferences in pollinators could offer new insights into their co-evolution with plants and the development of floral traits. More broadly, further research is needed on how pollinators respond to variability and unpredictability in neutral cues like scent or colour, a largely overlooked aspect of foraging decision-making.
... In this context, the scent profiles of generalist plants tend to be more complex than those of plants with specialist pollination systems, as they must appeal to the preferences of diverse insect species. Some general scent attractants, particularly those associated with nectar feeding, are present in food-rewarding and food-deceptive orchid species-two common pollination strategies among orchids [32]. However, due to stabilizing selection, the scent bouquets of food-rewarding species appear less variable than those of species employing deceptive pollination strategies [33]. ...
... Table S1: Data on the pollination systems and the floral volatile compounds (collecting methodology, number of compounds) of Neottia ovata and 22 compared orchids; Table S2: The proportion of chemical compounds that appeared only once within the scent profiles of analyzed orchid species. References [17,26,28,29,32,34,58,71,79,80,[82][83][84][85][86][87][88][89][90][91][92][93] are cited in the Supplementary Materials. ...
Understanding the complexity of flower scent—a crucial attractant for pollinators and a key factor in ensuring plant reproduction—is an essential ecological task for highly endangered orchids. To address this issue, we studied the flower volatiles profile of Neottia ovata, a nectar-rewarding orchid known for its generalist pollination strategy. We then compared the chemical composition of N. ovata floral scent with scent data of other orchid species to place our findings in the context of general volatile attractants emitted by nectar-rewarding or food-deceptive species. Our results contribute to understanding the complexity of the N. ovata floral scent profile and provide valuable methodological insights. The scented bouquet of N. ovata comprises 100 compounds with a relatively consistent composition across the analyzed samples. It is rich in terpenes, including linalool and trans-/cis-sabinene hydrate, compounds commonly associated with generalized rewarding or food-deceptive pollination systems. Other terpenes identified include α- and β-pinene, limonene, and β-phellandrene, whose presence underscores the generalized nature of the floral scent. Interestingly, in the studied N. ovata populations, the dominance among terpenes is shifting markedly towards γ-terpinene, α-terpinene, and terpinene-4-ol, commonly found in essential oils and the floral scents of some supergeneralist-pollination plants. Aromatic compounds were less represented in the N. ovata scent profile and those of other orchids studied, though benzyl alcohol and benzaldehyde were noticeably more abundant. Aliphatic compounds composed the least prevalent fraction, showing a marked decreasing trend among nectar-rewarding species with generalized or specialized pollination systems. It is worth emphasizing that the applied methodology revealed an extensive group of low-frequency compounds in the N. ovata floral scent. This finding raises new ecological questions about the intraspecific diversity of floral scent profiles and sheds new light on the factors determining effective reproduction in this species of orchid.
... The significance of this higher variance is unclear but may suggest a relaxed selection to attract pollinators in females compared to males (Salzmann et al., 2007). A much stronger factor influencing bouquet composition was the interaction between sex and population, indicating that in some populations, male and female plants displayed marked differences in bouquet composition. ...
Although attractive scents play a crucial role in reproduction in insect‐pollinated plants, the degree of variation of this signal within and among populations remains understudied. Depending on the specifics of the reproductive system of the plant under scrutiny, it is possible to formulate predictions regarding this variation. In plants with separate sexes (dioecious species) and with highly specific pollination, one would predict (i) males to emit more scent than females, owing to sexual selection, (ii) scent bouquets to have a strictly similar composition between sexes, to guarantee efficient pollen transfer and (iii) variation of scent bouquet among populations that should mirror neutral genetic divergence.
These hypotheses were tested in the European fan palm, Chamaerops humilis, by collecting scent in eight populations from three regions, Spain, Sardinia and Sicily, quantifying densities of pollinators—Derelomus sp. and Meligethinus pallidulus—and genotyping the plants on a set of neutral markers.
Males emitted more scent than females. We detected some differences in bouquet composition between sexes, showing an imperfect inter‐sex mimicry in some populations. We also found a strong geographical effect, with individuals sampled in Sicily emitting a strikingly different scent bouquet, which contained high proportions of a volatile compound that was never detected in the other two regions.
Geographical variation of scent composition did not mirror neutral genetic structure: Sardinian and Spanish populations emitted similar scent bouquets but displayed very high levels of genetic differentiation. On the reverse, Sicilian populations showed both strong scent differences and appeared clearly genetically differentiated from populations found elsewhere, without any depletion in neutral genetic diversity.
Synthesis: Our study confirmed higher scent emission rates in males compared to females, consistent with expectations of sexual selection. However, we also discovered significant variation in the composition of the floral bouquet, which was unexpected given the highly specific pollination context. Together with observations of spatial genetic structure, these findings suggest a shift in plant‐pollinator interactions within the species across different regions.
... Among flower traits, colour is the most widely exploited in Batesian floral mimicry, followed by flower shape and inflorescence architecture (Jersáková et al. 2016). In contrast, scent chemistry appears to be of lesser importance in food mimicry, at least in the orchid systems that have been investigated so far (Galizia et al. 2005;Salzmann et al. 2007;Peter and Johnson 2008;Jersáková et al. 2012). Although a deceptive orchid may benefit from a general colour similarity with a rewarding species, which could help attract pollinators (Gumbert and Kunze 2001;Johnson et al. 2003), this facultative benefit (Dafni and Ivri 1981) is not the same as the adaptive resemblance seen in Batesian floral mimicry. ...
... One such molecule known for eliciting physiological and behavioural responses in a diverse range of insect pollinators is 1,4-dimethoxybenzene (1,4-DMB), a methoxylated aromatic volatile compound [8,9,[17][18][19]. It serves as a major floral volatile in plant species of several genera, including Salix [17,20], Lithophragma [21], Nelumbo [22], Catasetum [23], Allium [9], and Fragaria [24]. ...
... Pollinators are mainly bees that play a crucial role in transferring pollen from male to female flowers [31,33,34], and 1,4-DMB is likely involved in attracting them (e.g. Apis mellifera, Bombus terrestris) to the flowers [18,30,35], as was recently shown for a florivorous beetle that also visits Cucurbita flowers [30,[36][37][38]. Despite its pivotal role in pollinator attraction, the enzymes and substrates orchestrating the formation of this volatile compound remain unknown. ...
Background
Floral scents play a crucial role in attracting insect pollinators. Among the compounds attractive to pollinators is 1,4-dimethoxybenzene (1,4-DMB). It is a significant contributor to the scent profile of plants from various genera, including economically important Cucurbita species. Despite its importance, the biosynthetic pathway for the formation of 1,4-DMB was not elucidated so far.
Results
In this study we showed the catalysis of 1,4-DMB in the presence of 4-methoxyphenol (4-MP) by protein extract from Styrian oil pumpkin (Cucurbita pepo) flowers. Based on this finding, we identified a novel O-methyltransferase gene, Cp4MP-OMT, whose expression is highly upregulated in the volatile-producing tissue of pumpkin flowers when compared to vegetative tissues. OMT activity was verified by purified recombinant Cp4MP-OMT, illustrating its ability to catalyse the methylation of 4-MP to 1,4-DMB in the presence of cofactor SAM (S-(5′-adenosyl)-L-methionine).
Conclusions
Cp4MP-OMT is a novel O-methyltransferase from C. pepo, responsible for the final step in the biosynthesis of the floral scent compound 1,4-DMB. Considering the significance of 1,4-DMB in attracting insects for pollination and in the further course fruit formation, enhanced understanding of its biosynthetic pathways holds great promise for both ecological insights and advancements in plant breeding initiatives.
... Electrophysiological studies with non-cucurbit plants, that, however, released compounds also identified from cucurbit flowers, have shown that several of such compounds are physiologically and / or behaviourally active in bumblebees. Among these compounds are the monoterpenes (E)-β-ocimene, (Z)-β-ocimene, linalool, β-myrcene, limonene, linalool oxide and α-pinene (Arpaia et al., 2011;Byers et al., 2014;Dormont et al., 2020;Suchet et al., 2011), the aromatic compounds benzaldehyde, 1,4-dimethoxybenzene and anisaldehyde (Montgomery et al., 2021;Salzmann et al., 2007), the aliphatic compound (Z)-3-hexenyl acetate, and the miscellaneous cyclic (Z)-jasmone (Arpaia et al., 2011;Dormont et al., 2020;Ferrari et al., 2006). ...
Fruiting of most cucurbits, among them several commercially used species, relies on animals that transfer pollen
from male to female flowers. To attract their pollinators, many cucurbits produce large, colorful and scented
flowers, which, however, also attract florivores. Knowing the flower visitors and understanding the specific
signals, including their biosynthesis, attractive to pollinators and florivores might be useful when aiming to
increase pollination and fruiting by ecological measures, breeding and genetic engineering. This review summarizes
the knowledge available on floral pigments, scents and visitors of cucurbits. We also review the genetic
basis of floral pigment and scent production as well as the role of floral colors and scents in attracting pollinators
and florivores. Floral visitors and colors are quite well studied, but there is very limited knowledge on the
biosynthesis of the various floral scent compounds described and the cues used by the different flower visitors to
find cucurbit flowers.
... First, pollinators can quickly learn to associate scent with a food source (reviewed in Wright & Schiestl, 2009), which may generate selection for scent emission in rewarding species. Second, non-rewarding species are frequently scentless (Wright & Schiestl, 2009) or emit variable scent which pollinators cannot associate with rewards (Salzmann et al., 2007). If scent production has metabolic (Gershenzon, 1994;Vogel, 1983) or ecological costs (Kessler et al., 2013), then low or variable scent may reflect selection to reduce these costs where scent does not serve as an honest signal due to a lack of rewards. ...
In flowering plants that produce concealed rewards, pollinator foraging preferences may select for floral advertisement traits that are correlated with rewards. To date, studies have not focused on the potential for honest signals to vary across populations, which could occur due to differences in pollinator communities or plant mating system.
We tested for variation in honest signals across and within populations and mating systems in Arabis alpina, a broadly distributed arctic‐alpine perennial herb that is visited by a variable community of insects. In a greenhouse common garden, we tested for correlations between corolla area, floral scent and nectar volume in 29 populations. In 12 field populations, we examined variation in pollen limitation and corolla area.
Across and within populations and mating systems, larger flowers generally produced more nectar. Total scent emission was not correlated with nectar production, but two compounds—phenylacetaldehyde and benzyl alcohol—may be honest signals in some populations. Corolla area was correlated with pollen limitation only across populations.
Our results suggest that honest signals may be similar across populations but may not result from contemporary direct selection on floral advertisements.
Read the free Plain Language Summary for this article on the Journal blog.
... Numerous studies have shown that olfactory signals can work together with visual signals to increase pollinator discrimination [5][6][7][8][9]. Conversely, several food-deceptive species that resemble the visual signals of model species produce scents that differ greatly to prevent inhibitory learning [10,11]. Therefore, the visual signal is the primary determinant of pollination success in food deception, while the role of olfactory signals varies among species [5,6,12]. ...
... The visual signal is also the major factor in the pollination success of food deception orchids [5,6,12]. The pollination accomplishment of food deceptive orchids, Anacamptis (Orchis) morio, is influenced by the proximity to rewarding plants and the similarity of flower color to that of magnet plants, while also emitting a highly variable scent to avoid pollinator learning and selective behavior [10,11]. Diuris brumalis is a food-deceptive orchid that attracts pollinators using visual signals similar to Daviesia decurrens at close range and ultraviolet visual signals at long range [32,33]. ...
Food-deceptive flowers primarily use visual signals (such as color) to mimic model plants and deceive insects into achieving pollination. Paphiopedilum micranthum is a food-deceptive orchid that has a pink labellum and two purple petals with a yellow base and has been proven to be pollinated by bumblebees. However, the chemical and molecular bases of the floral color are not well understood. We conducted targeted metabolite profiling and transcriptomic analysis to determine the color signal and its genetic basis in P. micranthum. We found that both anthocyanins and carotenoids contribute significantly to the formation of floral color that determines the color signal. Higher concentrations of anthocyanins (cyanidin and peonidin) and carotenoids (primarily lutein and zeaxanthin) were detected in the petal compared to the labellum. The upregulation of structural genes of CHS, F3′H, DFR and ANS on the anthocyanin biosynthesis pathway in petals was identified, as well as three genes of LCYE, BCH, and CCD4 on the carotenoid biosynthesis pathway. Furthermore, we discovered that three R2R3-MYBs and one bHLH transcription factors were co-expressed with the expression of different genes. These genes and transcription factors may be responsible for the spatial color difference of P. micranthum. Our study emphasizes that the color of this food-deceptive orchids is achieved through specific genes and transcription factors associated with the pigment biosynthesis pathway.
... Floral scent can influence pollinator behavior in several ways, besides simple attraction. It has been shown that smell increases their attention to visual stimuli (Salzmann et al. 2007) by influencing their landing and feeding behavior (Raguso and Willis 2005;Andersson and Dobson 2003;Dobson et al. 1999;Nilsson 1983a;Lunau 1992). Much is known about the role played by the shape and color of flowers in the ecology of pollination (Dobson 2006;Faegri and Van der Pijl 1979) while little is known about the chemical composition and ecological functions of floral odor, a deficiency due to much of its high chemical complexity and its multiple functions ranging from the attraction of pollinators, to the chemical defense against herbivores and pathogens, up to including the 'biochemical noise' introduced by the often low specificity of the enzymes that produce odorous floral compounds (Salzmann et al. 2007;Raguso 2003). ...
... It has been shown that smell increases their attention to visual stimuli (Salzmann et al. 2007) by influencing their landing and feeding behavior (Raguso and Willis 2005;Andersson and Dobson 2003;Dobson et al. 1999;Nilsson 1983a;Lunau 1992). Much is known about the role played by the shape and color of flowers in the ecology of pollination (Dobson 2006;Faegri and Van der Pijl 1979) while little is known about the chemical composition and ecological functions of floral odor, a deficiency due to much of its high chemical complexity and its multiple functions ranging from the attraction of pollinators, to the chemical defense against herbivores and pathogens, up to including the 'biochemical noise' introduced by the often low specificity of the enzymes that produce odorous floral compounds (Salzmann et al. 2007;Raguso 2003). W. Chase, 1997, are deceptive orchids from a food point of view. ...
... In a study performed by using the thermal desorption of the compounds absorbed on a trap on A. coriophora, 1,4-dimethoxybenzene and 4-methoxybenzaldehyde were the main components, while 1,2,4-trimethoxybenzene was found in less amount (Joffard et al. 2020). 4-Methoxybenzaldehyde was found as an important component of the scent in another study performed by using chemical desorption of the compounds absorbed on Porapak Q (Salzmann et al. 2007). These compounds were found also in our study, but they are not the main components. ...
The scent of Anacamptis species has been analyzed by using HS-SPME-GC-MS. The sample was collected in Basilicata (Southern Italy). Every species showed a different composition of the scent in the analyses we performed. 1,2,4-Trimethoxybenzene and methyl 4-mehoxybenzoate were the main components of that of Anacamptis coriophora subsp. fragrans. The scent of Anacamptis laxiflora was due to the presence of caryophyllene. Linear hydrocarbons but also decanal were components of the scent of Anacamptis pyramidalis. Eucalyptol was found in the scent of Anacamptis papilonacea. Finally, β-sesquiphellandrene was the main component of the scent of Anacamptis morio.
