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Francisco A, Ascensão L. Osmophore Structure and Labellum Micromorphology in Ophrys speculum (Orchidaceae): New Interpretations of Floral Features and Implications for a Specific Sexually Deceptive Pollination Interaction. PLANTS (BASEL, SWITZERLAND) 2024; 13:1413. [PMID: 38794483 PMCID: PMC11125028 DOI: 10.3390/plants13101413] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2024] [Revised: 05/12/2024] [Accepted: 05/14/2024] [Indexed: 05/26/2024]
Abstract
Pollination by sexual deception specifically attracts male insects, through the floral scent and particular morphological features of the flower that serve as visual and tactile stimuli. The unique bond between the Ophrys speculum orchid and the male Dasyscolia ciliata wasp primarily stems from a few distinctive semiochemicals that mimic the female wasp's sex pheromone, although the floral scent comprises a variety of compounds. An osmophore producing highly volatile compounds has been documented in four close relatives of O. speculum and is now being also investigated in this species. Given the existing debates regarding the structure of the labellum and stigmatic cavity in O. speculum, this study details their micromorphology. Additionally, comparisons of O. speculum flowers and female D. ciliata wasps under stereomicroscopy and scanning electron microscopy are conducted to seek new evidence of visual and tactile mimicry. The findings confirm that (i) an osmophore is present at the apical margin of the labellum in O. speculum flowers; (ii) the labellum features a distinct basal field homologous to those found in other Ophrys species; and (iii) the basal labellum region closely mimics the female wasp's thorax and wings. The implications of these novel floral features are discussed within an evolutionary context.
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Affiliation(s)
- Ana Francisco
- Centro de Estudos do Ambiente e do Mar (CESAM Lisboa), Faculdade de Ciências da Universidade de Lisboa (FCUL), C2, Campo Grande, 1749-016 Lisboa, Portugal
| | - Lia Ascensão
- Centro de Estudos do Ambiente e do Mar (CESAM Lisboa), Faculdade de Ciências da Universidade de Lisboa (FCUL), C2, Campo Grande, 1749-016 Lisboa, Portugal
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Wolcott KA, Stanley EL, Gutierrez OA, Wuchty S, Whitlock BA. 3D pollination biology using micro-computed tomography and geometric morphometrics in Theobroma cacao. APPLICATIONS IN PLANT SCIENCES 2023; 11:e11549. [PMID: 37915432 PMCID: PMC10617321 DOI: 10.1002/aps3.11549] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/04/2023] [Revised: 06/05/2023] [Accepted: 06/13/2023] [Indexed: 11/03/2023]
Abstract
Premise Imaging technologies that capture three-dimensional (3D) variation in floral morphology at micro- and nano-resolutions are increasingly accessible. In herkogamous flowers, such as those of Theobroma cacao, structural barriers between anthers and stigmas represent bottlenecks that restrict pollinator size and access to reproductive organs. To study the unresolved pollination biology of cacao, we present a novel application of micro-computed tomography (micro-CT) using floral dimensions to quantify pollinator functional size limits. Methods We generated micro-CT data sets from field-collected flowers and museum specimens of potential pollinators. To compare floral variation, we used 3D Slicer to place landmarks on the surface models and performed a geometric morphometric (GMM) analysis using geomorph R. We identified the petal side door (an opening between the petal hoods and filament) as the main bottleneck for pollinator access. We compared its mean dimensions with proposed pollinators to identify viable candidates. Results We identified three levels of likelihood for putative pollinators based on the number of morphological (body) dimensions that fit through the petal side door. We also found floral reward microstructures whose presence and location were previously unclear. Discussion Using micro-CT and GMM to study the 3D pollination biology of cacao provides new evidence for predicting unknown pollinators. Incorporating geometry and floral rewards will strengthen plant-pollinator trait matching models for cacao and other species.
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Affiliation(s)
| | - Edward L. Stanley
- Department of Natural HistoryFlorida Museum of Natural HistoryGainesvilleFloridaUSA
| | - Osman A. Gutierrez
- Subtropical Horticultural Research StationUnited States Department of Agriculture–Agricultural Research Service (USDA‐ARS)MiamiFlorida33158USA
| | - Stefan Wuchty
- Department of BiologyUniversity of MiamiCoral GablesFlorida33124USA
- Department of Computer ScienceUniversity of MiamiCoral GablesFlorida33146USA
- Institute of Data Science and ComputingUniversity of MiamiCoral GablesFlorida33146USA
- Sylvester Comprehensive Cancer CenterUniversity of MiamiMiamiFlorida33136USA
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Morphological Continua Make Poor Species: Genus-Wide Morphometric Survey of the European Bee Orchids ( Ophrys L.). BIOLOGY 2023; 12:biology12010136. [PMID: 36671828 PMCID: PMC9855528 DOI: 10.3390/biology12010136] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/29/2022] [Revised: 01/03/2023] [Accepted: 01/09/2023] [Indexed: 01/17/2023]
Abstract
Despite (or perhaps because of) intensive multidisciplinary research, opinions on the optimal number of species recognised within the Eurasian orchid genus Ophrys range from nine to at least 400. The lower figure of nine macrospecies is based primarily on seeking small but reliable discontinuities in DNA 'barcode' regions, an approach subsequently reinforced and finessed via high-throughput sequencing studies. The upper figure of ca. 400 microspecies reflects the morphological authoritarianism of traditional taxonomy combined with belief in extreme pollinator specificity caused by reliance on pollination through pseudo-copulation, enacted by bees and wasps. Groupings of microspecies that are less inclusive than macrospecies are termed mesospecies. Herein, we present multivariate morphometric analyses based on 51 characters scored for 457 individual plants that together span the full morphological and molecular diversity within the genus Ophrys, encompassing 113 named microspecies that collectively represent all 29 mesospecies and all nine macrospecies. We critique our preferred morphometric approach of accumulating heterogeneous data and analysing them primarily using principal coordinates, noting that our conclusions would have been strengthened by even greater sampling and the inclusion of data describing pseudo-pheromone cocktails. Morphological variation within Ophrys proved to be exceptionally multidimensional, lacking strong directional trends. Multivariate clustering of plants according to prior taxonomy was typically weak, irrespective of whether it was assessed at the level of macrospecies, mesospecies or microspecies; considerable morphological overlap was evident even between subsets of the molecularly differentiable macrospecies. Characters supporting genuine taxonomic distinctions were often sufficiently subtle that they were masked by greater and more positively correlated variation that reflected strong contrasts in flower size, tepal colour or, less often, plant size. Individual macrospecies appear to represent morphological continua, within which taxonomic divisions are likely to prove arbitrary if based exclusively on morphological criteria and adequately sampled across their geographic range. It remains unclear how much of the mosaic of subtle character variation among the microspecies reflects genetic versus epigenetic or non-genetic influences and what proportion of any contrasts observed in gene frequencies can be attributed to the adaptive microevolution that is widely considered to dictate speciation in the genus. Moreover, supplementing weak morphological criteria with extrinsic criteria, typically by imposing constraints on geographic location and/or supposed pollinator preference, assumes rather than demonstrates the presence of even the weakest of species boundaries. Overall, it is clear that entities in Ophrys below the level of macrospecies have insufficiently structured variation, either phenotypic or genotypic, to be resolved into discrete, self-circumscribing ("natural") entities that can legitimately be equated with species as delimited within other less specialised plant genera. Our search for a non-arbitrary (meso)species concept competent to circumscribe an intermediate number of species has so far proven unsuccessful.
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Joffard N, Buatois B, Arnal V, Véla E, Montgelard C, Schatz B. Delimiting species in the taxonomically challenging orchid section Pseudophrys: Bayesian analyses of genetic and phenotypic data. Front Ecol Evol 2022. [DOI: 10.3389/fevo.2022.1058550] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Accurate species delimitation is critical for biodiversity conservation. Integrative taxonomy has been advocated for a long time, yet tools allowing true integration of genetic and phenotypic data have been developed quite recently and applied to few models, especially in plants. In this study, we investigated species boundaries within a group of twelve Pseudophrys taxa from France by analyzing genetic, morphometric and chemical (i.e., floral scents) data in a Bayesian framework using the program integrated Bayesian Phylogenetics and Phylogeography (iBPP). We found that these twelve taxa were merged into four species when only genetic data were used, while most formally described species were recognized as such when only phenotypic (either morphometric or chemical) data were used. The result of the iBPP analysis performed on both genetic and phenotypic data supports the proposal to merge Ophrys bilunulata and O. marmorata on the one hand, and O. funerea and O. zonata on the other hand. Our results show that phenotypic data are particularly informative in the section Pseudophrys and that their integration in a model-based method significantly improves the accuracy of species delimitation. We are convinced that the integrative taxonomic approach proposed in this study holds great promise to conduct taxonomic revisions in other orchid groups.
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Are some species ‘robust’ to exploitation? Explaining persistence in deceptive relationships. Evol Ecol 2022. [DOI: 10.1007/s10682-022-10174-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
AbstractAnimals and plants trick others in an extraordinary diversity of ways to gain fitness benefits. Mimicry and deception can, for example, lure prey, reduce the costs of parental care or aid in pollination–in ways that impose fitness costs on the exploited party. The evolutionary maintenance of such asymmetric relationships often relies on these costs being mitigated through counter-adaptations, low encounter rates, or indirect fitness benefits. However, these mechanisms do not always explain the evolutionary persistence of some classic deceptive interactions.Sexually deceptive pollination (in which plants trick male pollinators into mating with their flowers) has evolved multiple times independently, mainly in the southern hemisphere and especially in Australasia and Central and South America. This trickery imposes considerable costs on the males: they miss out on mating opportunities, and in some cases, waste their limited sperm on the flower. These relationships appear stable, yet in some cases there is little evidence suggesting that their persistence relies on counter-adaptations, low encounter rates, or indirect fitness benefits. So, how might these relationships persist?Here, we introduce and explore an additional hypothesis from systems biology: that some species are robust to exploitation. Robustness arises from a species’ innate traits and means they are robust against costs of exploitation. This allows species to persist where a population without those traits would not, making them ideal candidates for exploitation. We propose that this mechanism may help inform new research approaches and provide insight into how exploited species might persist.
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Martel C, Rakosy D, Dötterl S, Johnson SD, Ayasse M, Paulus HF, Nilsson LA, Mejlon H, Jersáková J. Specialization for Tachinid Fly Pollination in the Phenologically Divergent Varieties of the Orchid Neotinea ustulata. Front Ecol Evol 2021. [DOI: 10.3389/fevo.2021.659176] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Despite increased focus on elucidating the various reproductive strategies employed by orchids, we still have only a rather limited understanding of deceptive pollination systems that are not bee- or wasp-mediated. In Europe, the orchid Neotinea ustulata has been known to consist of two phenologically divergent varieties, neither of which provide rewards to its pollinators. However, detailed studies of their reproductive biology have been lacking. Our study aimed to characterize and understand the floral traits (i.e., morphology, color, and scent chemistry) and reproductive biology of N. ustulata. We found that the two varieties differ in all their floral traits; furthermore, while Neotinea ustulata var. ustulata appears to be pollinated by both bees (e.g., Anthophora, Bombus) and flies (e.g., Dilophus, Tachina), var. aestivalis is pollinated almost entirely by flies (i.e., Nowickia, Tachina). Tachinids were also found to be much more effective than bees in removing pollinaria, and we show experimentally that they use the characteristic dark inflorescence top as a cue for approaching inflorescences. Our results thus suggest that while both N. ustulata varieties rely on tachinids for pollination, they differ in their degree of specialization. Further studies are, however, needed to fully understand the reproductive strategy of N. ustulata varieties.
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Luo H, Xiao H, Liang Y, Liu N, Turner C, Tan S, Chen X, Xiong D, Yang B. Batesian mimicry in the nonrewarding saprophytic orchid Danxiaorchis yangii. Ecol Evol 2021; 11:2524-2534. [PMID: 33767819 PMCID: PMC7981215 DOI: 10.1002/ece3.7193] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2020] [Revised: 11/17/2020] [Accepted: 12/21/2020] [Indexed: 11/08/2022] Open
Abstract
Batesian mimicry, a type of deceptive pollination, is a complicated strategy used by nonrewarding plants to attract pollinators, but some hypotheses concerning this have not been systematically verified. In order to show in detail a case of Batesian mimicry on saprophytic orchid Danxiaorchis yangii, the ecological relationship between Danxiaorchis yangii, Lysimachia alfredi and Dufourea spp. was explored. Lysimachia alfredi could provide a reward to Dufourea sp., whereas Danxiaorchis yangii not. The floral morphology and geographical distribution of these two plants were highly overlapping, and the fruit set rate of Danxiaorchis yangii was significantly positively correlated with the number of nearby L. alfredi individuals. In a glass cylinder experiment, Danxiaorchis yangii and L. alfredi attracted Dufourea spp. through visual signals, but the insect could not distinguish between flowers of the two plants before landing on flowers. The ultraviolet reflection spectra of flowers between the two plant species were highly similar. In the hexagonal color models constructed according to the visual characteristics of bees, the flower color signals of these two plant species highly overlap, indicating that the visual signals of the flowers of the two plants to the pollinator were greatly similar. All of these results provided evidence that Danxiaorchis yangii simulated the visual signals of L. alfredi through Batesian mimicry, thereby deceptively attracting Dufourea spp.
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Affiliation(s)
- Huolin Luo
- Jiangxi Key Laboratory of Plant ResourcesSchool of Life ScienceNanchang UniversityNanchangChina
| | - Hanwen Xiao
- Jiangxi Key Laboratory of Plant ResourcesSchool of Life ScienceNanchang UniversityNanchangChina
| | - Yuelong Liang
- Jiangxi Jiulianshan National Nature ReserveGanzhouChina
| | - Nannan Liu
- Jiangxi Key Laboratory of Plant ResourcesSchool of Life ScienceNanchang UniversityNanchangChina
| | - Cassidy Turner
- College of Health SolutionsArizona State UniversityScottsdaleAZUSA
| | - Shaolin Tan
- Jiangxi Key Laboratory of Plant ResourcesSchool of Life ScienceNanchang UniversityNanchangChina
| | - Xinghui Chen
- Jiangxi Key Laboratory of Plant ResourcesSchool of Life ScienceNanchang UniversityNanchangChina
| | - Dongjin Xiong
- Jiangxi Key Laboratory of Plant ResourcesSchool of Life ScienceNanchang UniversityNanchangChina
| | - Boyun Yang
- Jiangxi Key Laboratory of Plant ResourcesSchool of Life ScienceNanchang UniversityNanchangChina
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Baguette M, Bertrand JAM, Stevens VM, Schatz B. Why are there so many bee-orchid species? Adaptive radiation by intra-specific competition for mnesic pollinators. Biol Rev Camb Philos Soc 2020; 95:1630-1663. [PMID: 32954662 DOI: 10.1111/brv.12633] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Revised: 06/09/2020] [Accepted: 06/15/2020] [Indexed: 01/08/2023]
Abstract
Adaptive radiations occur mostly in response to environmental variation through the evolution of key innovations that allow emerging species to occupy new ecological niches. Such biological innovations may play a major role in niche divergence when emerging species are engaged in reciprocal ecological interactions. To demonstrate coevolution is a difficult task; only a few studies have confirmed coevolution as driver of speciation and diversification. Herein we review current knowledge about bee orchid (Ophrys spp.) reproductive biology. We propose that the adaptive radiation of the Mediterranean orchid genus Ophrys, comprising several hundred species, is due to coevolutionary dynamics between these plants and their pollinators. We suggest that pollination by sexual swindling used by Ophrys orchids is the main driver of this coevolution. Flowers of each Ophrys species mimic a sexually receptive female of one particular insect species, mainly bees. Male bees are first attracted by pseudo-pheromones emitted by Ophrys flowers that are similar to the sexual pheromones of their females. Males then are lured by the flower shape, colour and hairiness, and attempt to copulate with the flower, which glues pollen onto their bodies. Pollen is later transferred to the stigma of another flower of the same Ophrys species during similar copulation attempts. In contrast to rewarding pollination strategies, Ophrys pollinators appear to be parasitized. Here we propose that this apparent parasitism is in fact a coevolutionary relationship between Ophrys and their pollinators. For plants, pollination by sexual swindling could ensure pollination efficiency and specificity, and gene flow among populations. For pollinators, pollination by sexual swindling could allow habitat matching and inbreeding avoidance. Pollinators might use the pseudo-pheromones emitted by Ophrys to locate suitable habitats from a distance within complex landscapes. In small populations, male pollinators would disperse once they have memorized the local diversity of sexual pseudo-pheromone bouquets or if all Ophrys flowers are fertilized and thus repel pollinators via production of repulsive pheromones that mimic those produced by fertilized female bees. We propose the following evolutionary scenario: Ophrys radiation is driven by strong intra-specific competition among Ophrys individuals for the attraction of species-specific pollinators, which is a consequence of the high cognitive abilities of pollinators. Male bees record the pheromone signatures of kin or of previously courted partners to avoid further copulation attempts, thereby inducing strong selection on Ophrys for variation in odour bouquets emitted by individual flowers. The resulting odour bouquets could by chance correspond to pseudo-pheromones of the females of another bee species, and thus attract a new pollinator. If such pollinator shifts occur simultaneously in several indivuals, pollen exchanges might occur and initiate speciation. To reinforce the attraction of the new pollinator and secure prezygotic isolation, the following step is directional selection on flower phenotypes (shape, colour and hairiness) towards a better match with the body of the pollinator's female. Pollinator shift and the resulting prezygotic isolation is adaptive for new Ophrys species because they may benefit from competitor-free space for limited pollinators. We end our review by proritizing several critical research avenues.
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Affiliation(s)
- Michel Baguette
- Institut Systématique, Evolution, Biodiversité (ISYEB), UMR 7205 Museum National d'Histoire Naturelle, CNRS, Sorbonne Université, EPHE, Université des Antilles, F-75005, Paris, France.,Centre National de la Recherche Scientifique and Université Paul Sabatier Toulouse III, SETE Station d'Ecologie Théorique et Expérimentale, UMR 5321, F-09200, Moulis, France
| | - Joris A M Bertrand
- LGDP (Laboratoire Génome et Développement des Plantes) UMR5096, Université de Perpignan Via Domitia -CNRS, F-66860, Perpignan, France
| | - Virginie M Stevens
- Centre National de la Recherche Scientifique and Université Paul Sabatier Toulouse III, SETE Station d'Ecologie Théorique et Expérimentale, UMR 5321, F-09200, Moulis, France
| | - Bertrand Schatz
- CEFE (Centre d'Ecologie Fonctionnelle et Evolutive) UMR 5175, CNRS - Université de Montpellier - Université Paul Valéry - EPHE, 1919 Route de Mende, 34293, Montpellier, France
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Martel C, Neubig KM, Williams NH, Ayasse M. The uncinate viscidium and floral setae, an evolutionary innovation and exaptation to increase pollination success in the Telipogon alliance (Orchidaceae: Oncidiinae). ORG DIVERS EVOL 2020. [DOI: 10.1007/s13127-020-00457-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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Orchid-pollinator network in Euro-Mediterranean region: What we know, what we think we know, and what remains to be done. ACTA OECOLOGICA-INTERNATIONAL JOURNAL OF ECOLOGY 2020. [DOI: 10.1016/j.actao.2020.103605] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Lussu M, De Agostini A, Cogoni A, Marignani M, Cortis P. Does size really matter? A comparative study on floral traits in orchids with two different pollination strategies. PLANT BIOLOGY (STUTTGART, GERMANY) 2019; 21:961-966. [PMID: 30945419 DOI: 10.1111/plb.12993] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2018] [Accepted: 03/31/2019] [Indexed: 06/09/2023]
Abstract
The lock and key hypothesis assumes that male and female genitalia match in a unique system to prevent interspecific crosses. This hypothesis is largely investigated in animals, while there is a distinct lack of studies on plants. Nevertheless, we expect the lock and key hypothesis could apply to plants with complex floral morphologies, such as orchids. Here we apply a comparative approach to examine the variation of floral functional traits in food- and sex-deceptive orchids. To understand if a specific deception strategy is related to a specific variation in floral traits evaluated the variation in sterile and fertile traits among species and subsequently examined the correlations between male and female reproductive organs of the same species with the aim of investigating the role of the lock and key hypothesis in deceptive orchids. Our results show that the functional morphology of fertile traits plays a pivotal role in limiting gene flow in species that grow in sympatry. In particular, it was observed that the Reproductive Standardisation Index (RSI) is significantly different in the two pollination strategies and that the correlation between pollinarium length and stigmatic cavity length is stronger in food-deceptive species when compared to the sex-deceptive species. These results reveal that the lock and key hypothesis contributes to maintain boundaries in plants with very complex floral morphology.
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Affiliation(s)
- M Lussu
- Department of Life and Environmental Sciences, University of Cagliari, Cagliari, Italy
| | - A De Agostini
- Department of Life and Environmental Sciences, University of Cagliari, Cagliari, Italy
| | - A Cogoni
- Department of Life and Environmental Sciences, University of Cagliari, Cagliari, Italy
| | - M Marignani
- Department of Life and Environmental Sciences, University of Cagliari, Cagliari, Italy
| | - P Cortis
- Department of Life and Environmental Sciences, University of Cagliari, Cagliari, Italy
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de Jager ML, Peakall R. Experimental examination of pollinator-mediated selection in a sexually deceptive orchid. ANNALS OF BOTANY 2019; 123:347-354. [PMID: 29878057 PMCID: PMC6344214 DOI: 10.1093/aob/mcy083] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2017] [Accepted: 04/30/2018] [Indexed: 05/11/2023]
Abstract
BACKGROUND AND AIMS Selection exerted by pollinators on flowers is predicted to occur along two distinct axes. While pollinator attraction to flowers is governed by pollinator preferences, pollen transfer efficiency is mediated by the mechanical fit of pollinators to flower morphology. Although pollinator attraction in sexually deceptive orchids is typically underpinned by floral odour, morphological traits are expected to play a vital role in mechanical fit during floral contact with pollinators. METHODS Here we utilize a comprehensive and novel procedure to test for pollinator-mediated selection through mechanical fit with the flower labellum in the orchid Chiloglottis trapeziformis. This approach combines detailed pollinator observations related to plant reproductive fitness with complementary experimental manipulation and phenotypic selection analysis. KEY RESULTS Experiments with virgin flowers revealed that pollen removal occurs only during vigorous pseudocopulation. This behaviour involves male wasps that grasp the insectiform callus structure on the labellum while probing the labellum tip in a forward orientation. Both orientation and duration of pseudocopulation were significant predictors of pollen removal, confirming a direct relationship between pollinator behaviour and plant fitness. Controlled floral manipulation that either shortened or elongated the distance between the callus and the labellum tip detected no change in pollinator attraction. The duration of pseudocopulation, however, was significantly reduced on flowers with shortened or elongated callus-tip distances, consistent with stabilizing selection. Phenotypic selection analysis confirmed this prediction in natural populations by uncovering evidence for stabilizing selection on the distance between the callus and the labellum tip. CONCLUSIONS Our experimental manipulations and selection analysis in natural populations thus demonstrate stabilizing selection on the distance from the callus to the labellum tip, and illustrate the utility of employing multiple approaches to confirm selection exerted by pollinators on floral form.
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Affiliation(s)
- Marinus L de Jager
- Department of Botany and Zoology, Stellenbosch University, Matieland, South Africa
- For correspondence. E-mail
| | - Rod Peakall
- Ecology and Evolution, Research School of Biology, The Australian National University, Acton, ACT, Australia
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Scaccabarozzi D, Cozzolino S, Guzzetti L, Galimberti A, Milne L, Dixon KW, Phillips RD. Masquerading as pea plants: behavioural and morphological evidence for mimicry of multiple models in an Australian orchid. ANNALS OF BOTANY 2018; 122:1061-1073. [PMID: 30184161 PMCID: PMC6266105 DOI: 10.1093/aob/mcy166] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2018] [Accepted: 08/12/2018] [Indexed: 05/03/2023]
Abstract
Background and Aims While there is increasing recognition of Batesian floral mimicry in plants, there are few confirmed cases where mimicry involves more than one model species. Here, we test for pollination by mimicry in Diuris (Orchidaceae), a genus hypothesized to attract pollinators via mimicry of a range of co-occurring pea plants (Faboideae). Methods Observations of pollinator behaviour were made for Diuris brumalis using arrays of orchid flowers. An analysis of floral traits in the co-flowering community and spectral reflectance measurements were undertaken to test if Di. brumalis and the pea plants showed strong similarity and were likely to be perceived as the same by bees. Pollen removal and fruit-set were recorded at 18 sites over two years to test if fitness of Di. brumalis increased with the abundance of the model species. Key Results Diuris brumalis shares the pollinator species Trichococolletes capillosus and T. leucogenys (Hymenoptera: Colletidae) with co-flowering Faboideae from the genus Daviesia. On Di. brumalis, Trichocolletes exhibited the same stereotyped food-foraging and mate-patrolling behaviour that they exhibit on Daviesia. Diuris and pea plants showed strong morphological similarity compared to the co-flowering plant community, while the spectral reflectance of Diuris was similar to that of Daviesia spp. Fruit-set and pollen removal of Di. brumalis was highest at sites with a greater number of Daviesia flowers. Conclusions Diuris brumalis is pollinated by mimicry of co-occurring congeneric Faboideae species. Evidence for mimicry of multiple models, all of which share pollinator species, suggests that this may represent a guild mimicry system. Interestingly, Di. brumalis belongs to a complex of species with similar floral traits, suggesting that this represents a useful system for investigating speciation in lineages that employ mimicry of food plants.
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Affiliation(s)
- Daniela Scaccabarozzi
- Department of Environment and Agriculture, Curtin University, Bentley, WA, Australia
- Department of Biology, University of Naples Federico II, Complesso Universitario MSA, Naples, Italy
- Kings Park and Botanic Garden, The Botanic Garden and Parks Authority, West Perth, WA, Australia
| | - Salvatore Cozzolino
- Department of Biology, University of Naples Federico II, Complesso Universitario MSA, Naples, Italy
| | - Lorenzo Guzzetti
- Università degli Studi di Milano-Bicocca, ZooPlantLab, Dipartimento di Biotecnologie e Bioscienze, Piazza della Scienza, Milano, Italy
| | - Andrea Galimberti
- Università degli Studi di Milano-Bicocca, ZooPlantLab, Dipartimento di Biotecnologie e Bioscienze, Piazza della Scienza, Milano, Italy
| | - Lynne Milne
- School of Earth and Planetary Sciences, Curtin University, Bentley, WA, Australia
| | - Kingsley W Dixon
- Department of Environment and Agriculture, Curtin University, Bentley, WA, Australia
| | - Ryan D Phillips
- Kings Park and Botanic Garden, The Botanic Garden and Parks Authority, West Perth, WA, Australia
- Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Canberra, ACT, Australia
- Department of Ecology, Environment and Evolution, La Trobe University, Vic., Australia
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Phillips RD, Peakall R. An experimental evaluation of traits that influence the sexual behaviour of pollinators in sexually deceptive orchids. J Evol Biol 2018; 31:1732-1742. [PMID: 30144355 DOI: 10.1111/jeb.13370] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2017] [Accepted: 08/20/2018] [Indexed: 12/20/2022]
Abstract
Pollination by sexual deception of male insects is perhaps one of the most remarkable cases of mimicry in the plant kingdom. However, understanding the influence of floral traits on pollinator behaviour in sexually deceptive plants is challenging, due to the risk of confounding changes in floral odour when manipulating morphology. Here, we investigated the floral traits influencing the sexual response of male Zaspilothynnus nigripes (Tiphiidae) wasps, a pollinator of two distantly related sexually deceptive orchids with contrasting floral architecture, Caladenia pectinata and Drakaea livida. In D. livida, the chemical sexual attractant is emitted from the labellum, whereas in C. pectinata, it is produced from the distal sepal tips, allowing manipulative experiments. When controlling for visual cues, there was no difference in long-distance attraction, although the floral odour of D. livida induced copulation more frequently than that of C. pectinata. The role of colour in pollinator sexual attraction was equivocal, indicating that colour may not be a strong constraint on the initial evolution of sexual deception. The frequency of wasp visitors landing on C. pectinata decreased when the amount of floral odour was reduced, but attempted copulation rates were enhanced when the source of floral odour was associated with the labellum. These latter variables may represent axes of selection that operate across many sexually deceptive species. Nonetheless, the observed variation in floral traits suggests flexibility among species in how sexual deception can be achieved.
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Affiliation(s)
- Ryan D Phillips
- Ecology and Evolution, Research School of Biology, The Australian National University, Canberra, ACT, Australia.,Kings Park and Botanic Garden, The Botanic Garden and Parks Authority, West Perth, WA, Australia.,Department of Ecology, Environment & Evolution, La Trobe University, Bundoora, VIC, Australia
| | - Rod Peakall
- Ecology and Evolution, Research School of Biology, The Australian National University, Canberra, ACT, Australia
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