Getting hooked? Testing the function of anther spurs in Vaccinium myrtillus

Lisette van Kolfschoten; Mario Vallejo-Marin

doi:10.26786/1920-7603(2025)894

Authors

Lisette van Kolfschoten Uppsala University https://orcid.org/0000-0002-1751-6551
Mario Vallejo-Marin https://orcid.org/0000-0002-5663-8025

DOI:

https://doi.org/10.26786/1920-7603(2025)894

Keywords:

Anther morphology, Bombus, buzz pollination, pollen removal, spur, Vaccinium myrtillus

Abstract

Flowers display remarkable diversity, much of which is shaped by interactions with pollinators. While various floral traits are considered adaptations to pollination, the function of many morphological features remains untested. In buzz-pollinated species, where bees use vibrations to extract pollen, anther morphology is diverse and can influence pollen removal and transfer. Poricidal anthers, common in these species, sometimes bear spur-like projections. These spurs are hypothesized to aid pollen release, but this has not been experimentally tested. Here, we investigated the function of anther spurs in Vaccinium myrtillus (Ericaceae). Using a laboratory setup, we conducted two complementary experiments: one where Bombus terrestris bumblebees foraged on flowers, and another applying 1 s artificial vibrations to mimic bee buzzes. We compared pollen release between flowers with intact anther spurs and those where spurs had been removed. Bumblebees produced vibrations during 90% of visits, irrespective of spur presence. Buzzing visits were shorter (21.70 ± 24 s; mean ± SD) and removed more pollen (60 ± 29%) than non-buzzing visits, which were three times longer (63.79 ± 70.45 s) but removed 23 ± 43% of pollen. Artificial 1 s buzzes removed an average of 23% of pollen. Spur removal increased pollen release in both the bee (54% to 60%) and the artificial buzzing experiment (18% to 28%). Our results suggest that anther spurs in V. myrtillus potentially act as a pollen-dispensing mechanism, but this effect depends on bee behaviour and visit duration. Further studies could explore other roles the spur has in interactions with non-buzzing visitors, such as regulating pollen release when visitors collect nectar.

References

Bartholomée O, Björnberg J, Smith HG, Kendall L (2024) Pollinator effectiveness and pollination dependency of bilberry (Vaccinium myrtillus) in Swedish hemi-boreal forests. Journal of Pollination Ecology 35:135–143. DOI: https://doi.org/10.26786/1920-7603(2024)791

Bates D, Mächler M, Bolker B, Walker S (2015) Fitting Linear Mixed-Effects Models Using lme4. Journal of Statistical Software 67 DOI: https://doi.org/10.18637/jss.v067.i01

Beug HJ (2004) Leitfaden der Pollenbestimmung für Mitteleuropa und angrenzende Gebiete (Guide to the Pollen Analysis for Central Europe and the Adjacent Areas). Pfeil, München.

Bochorny T, Bacci LF, Dellinger AS, Michelangeli FA, Goldenberg R, Brito VLG (2021) Connective appendages in Huberia bradeana (Melastomataceae) affect pollen release during buzz pollination Ren Z-X (ed). Plant Biology 23:556–563. DOI: https://doi.org/10.1111/plb.13244

Bochorny T, Michelangeli FA, Almeda F, Goldenberg R (2019) Phylogenetics, morphology and circumscription of Cambessedesieae: a new Neotropical tribe of Melastomataceae. Botanical Journal of the Linnean Society 190:281–302. DOI: https://doi.org/10.1093/botlinnean/boz018

Bradshaw HD, Schemske DW (2003) Allele substitution at a flower colour locus produces a pollinator shift in monkeyflowers. Nature 426:176–178. DOI: https://doi.org/10.1038/nature02106

Buchmann SL (1983) Buzz pollination in angiosperms. Handbook of experimental pollination biology. In: Handbook of experimental pollination biology. 73–113.

Buchmann SL (1989) Original papers Bees assess pollen returns while sonicating Solanum flowers. Oecologia 81:289–294. DOI: https://doi.org/10.1007/BF00377073

Campbell DR, Bischoff M, Lord JM, Robertson AW (2010) Flower colour influences insect visitation in alpine New Zealand. Ecology 91:2638–2649. DOI: https://doi.org/10.1890/09-0941.1

Castellanos, MC, Wilson P, Keller SJ, Wolfe AD, Thomson JD (2006) Anther evolution: pollen presentation strategies when pollinators differ. The American Naturalist, 167:288-296. DOI: https://doi.org/10.1086/498854

Clausing G, Renner SS (2001) Molecular phylogenetics of Melastomataceae and Memecylaceae: implications for character evolution. American Journal of Botany 88:486–498. DOI: https://doi.org/10.2307/2657114

Conner JK, Sterling A (1995) Testing hypotheses of functional relationships: a comparative survey of correlation patterns among floral traits in five insect‐pollinated plants. American Journal of Botany 82:1399-1406. DOI: https://doi.org/10.1002/j.1537-2197.1995.tb12676.x

Da Rocha MJR, Guimarães PJF, Michelangeli FA, Nogueira Batista JA (2018) Taxonomy of Marcetieae: A New Neotropical Tribe of Melastomataceae. International Journal of Plant Sciences 179:50–74. DOI: https://doi.org/10.1086/694932

Dafni A (1984) Mimicry and Deception in Pollination. Annual Review of Ecology and Systematics 15:259–278. DOI: https://doi.org/10.1146/annurev.ecolsys.15.1.259

De Luca PA, Vallejo-Marín M (2013) What’s the ‘buzz’ about? The ecology and evolutionary significance of buzz-pollination. Current Opinion in Plant Biology 16:429–435. DOI: https://doi.org/10.1016/j.pbi.2013.05.002

Dellinger A, Penneys D, Staedler Y, Fragner L, Weckwerth W, Schönenberger J (2014) A Specialized Bird Pollination System with a Bellows Mechanism for Pollen Transfer and Staminal Food Body Rewards. Current Biology 24:1615–1619. DOI: https://doi.org/10.1016/j.cub.2014.05.056

Dorr LJ (1981) The Pollination Ecology of Zenobia (Ericaceae). American Journal of Botany 68:1325–1332. DOI: https://doi.org/10.1002/j.1537-2197.1981.tb07843.x

Faegri K (1986) The solanoid flower. Transactions of the Botanical Society of Edinburgh 45:51–59. DOI: https://doi.org/10.1080/03746608608684993

Galen C (1989) Measuring Pollinator-Mediated Selection on Morphometric Floral Traits: Bumblebees and the Alpine Sky Pilot, Polemonium viscosum. Evolution 43:882–890. DOI: https://doi.org/10.1111/j.1558-5646.1989.tb05185.x

Harder LD, Thomson JD (1989) Evolutionary Options for Maximizing Pollen Dispersal of Animal-Pollinated Plants. The American Naturalist 133:323–344. DOI: https://doi.org/10.1086/284922

Harder LD, Wilson WG (1994) Floral evolution and male reproductive success: Optimal dispensing schedules for pollen dispersal by animal-pollinated plants. Evolutionary Ecology 8:542–559. DOI: https://doi.org/10.1007/BF01238257

Hartig F (2016) DHARMa: residual diagnostics for hierarchical (multi-level/mixed) regression models. https://CRAN.R-project.org/package=DHARMa DOI: https://doi.org/10.32614/CRAN.package.DHARMa

Hempel De Ibarra N, Langridge KV, Vorobyev M (2015) More than colour attraction: behavioural functions of flower patterns. Current Opinion in Insect Science 12:64–70. DOI: https://doi.org/10.1016/j.cois.2015.09.005

Hermann PM, Palser BF (2000) Stamen development in the Ericaceae. I. Anther wall, microsporogenesis, inversion, and appendages. American Journal of Botany 87:934–957. DOI: https://doi.org/10.2307/2656993

Jankauski M, Ferguson R, Russell A, Buchmann S (2022) Structural dynamics of real and modelled Solanum stamens: implications for pollen ejection by buzzing bees. Journal of The Royal Society Interface 19:20220040. DOI: https://doi.org/10.1098/rsif.2022.0040

Johnson SD, Harder LD (2023) The economy of pollen dispersal in flowering plants. Proceedings of the Royal Society B: Biological Sciences 290 DOI: https://doi.org/10.1098/rspb.2023.1148

Judd WS (1979) Generic Relationships in the Andromedeae (Ericaceae). Journal of the Arnold Arboretum 60:477–503. DOI: https://doi.org/10.5962/p.185891

Kartonegoro A, Veldkamp JF, Hovenkamp P, Van Welzen P (2018) A revision of Dissochaeta (Melastomataceae, Dissochaeteae). PhytoKeys 107:1–178. DOI: https://doi.org/10.3897/phytokeys.107.26548.figure23

Kawai Y, Kudo G (2009) Effectiveness of buzz pollination in Pedicularis chamissonis : significance of multiple visits by bumblebees. Ecological Research 24:215–223. DOI: https://doi.org/10.1007/s11284-008-0500-6

Kern BR, Carley LN, Moeller DA (2023) Direct tracking of pollen with quantum dots reveals surprising uniformity in dispersal distance across 11 populations of an annual plant. American Journal of Botany 110 DOI: https://doi.org/10.1002/ajb2.16201

King MJ, Buchmann SL (1996) Sonication Dispensing of Pollen from Solanum laciniatum Flowers. Functional Ecology 10:449. DOI: https://doi.org/10.2307/2389937

Kuznetsova A, Brockhoff PB, Christensen RHB (2017) lmerTest Package: Tests in Linear Mixed Effects Models. Journal of Statistical Software 82 DOI: https://doi.org/10.18637/jss.v082.i13

Lenth RV (2024) emmeans: Estimated Marginal Means, aka Least-Squares Means. [online] URL: https://CRAN.R-project.org/package=emmeans

Lloyd DG, Yates JMA (1982) Intrasexual Selection and the Segregation of Pollen and Stigmas in Hermaphrodite Plants, Exemplified by Wahlenbergia albomarginata (Campanulaceae). 36:903–913. DOI: https://doi.org/10.1111/j.1558-5646.1982.tb05462.x

Lüdecke D (2023) sjPlot: data visualization for statistics in social science. R package version 2.8. 14 https://CRAN.R-project.org/package=sjPlot

Luo Z, Zhang D, Renner SS (2008) Why two kinds of stamens in buzz‐pollinated flowers? Experimental support for Darwin’s division‐of‐labour hypothesis. Functional Ecology 22:794–800. DOI: https://doi.org/10.1111/j.1365-2435.2008.01444.x

Melo LRF, Vasconcelos TNC, Caetano APS, De Brito VLG (2022) Stamen Diversity in Melastomataceae: Morphology, Colour, and Function. In: Goldenberg R, Michelangeli FA, Almeda F (eds) Systematics, Evolution, and Ecology of Melastomataceae. Springer International Publishing, Cham, pp 609–628. DOI: https://doi.org/10.1007/978-3-030-99742-7_27

Michelangeli FA, Guimaraes PJF, Penneys DS, Almeda F, Kriebel R (2013) Phylogenetic relationships and distribution of New World Melastomeae (Melastomataceae): New World Melastomeae (Melastomataceae). Botanical Journal of the Linnean Society 171:38–60. DOI: https://doi.org/10.1111/j.1095-8339.2012.01295.x

Michener CD (1962) An Interesting Method of Pollen Collecting by Bees from Flowers with Tubular Anthers. Revista De Biologia Tropical 10:165–175.

Minnaar C, Anderson B, De Jager ML, Karron JD (2019) Plant–pollinator interactions along the pathway to paternity. Annals of Botany 123:225–245. DOI: https://doi.org/10.1093/aob/mcy167

Moquet L, Bruyère L, Pirard B, Jacquemart A (2017) Nectar foragers contribute to the pollination of buzz‐pollinated plant species. American Journal of Botany 104:1451–1463. DOI: https://doi.org/10.3732/ajb.1700090

Moquet L, Vanderplanck M, Moerman R, Quinet M, Roger N, Michez D, Jacquemart A-L (2017) Bumblebees depend on ericaceous species to survive in temperate heathlands Schonrogge K, Brady S (eds). Insect Conservation and Diversity 10:78–93. DOI: https://doi.org/10.1111/icad.12201

Muchhala N (2007) Adaptive Trade‐Off in Floral Morphology Mediates Specialization for Flowers Pollinated by Bats and Hummingbirds. The American Naturalist 169. DOI: https://doi.org/10.1086/512047

Müller H (1873) Die Befruchtung der Blumen durch Insekten und die gegenseitigen Anpassungen beider: Ein Beitrag zur Erkenntnis des ursächlichen Zusammenhanges in der organischen Natur. W. Engelmann. 355-356. DOI: https://doi.org/10.5962/bhl.title.50246

Müller H (1883) Fertilization of flowers. Macmillan, London. DOI: https://doi.org/10.5962/bhl.title.142366

Passos LS, Telles FJ, Goldenberg R, Amano E, Maia FR (2022) What is the role of stamen appendages in the buzz-pollinated Huberia insignis (Melastomataceae)? Flora 293:152113. DOI: https://doi.org/10.1016/j.flora.2022.152113

Raguso RA (2008) Wake Up and Smell the Roses: The Ecology and Evolution of Floral Scent. Annual Review of Ecology, Evolution, and Systematics 39:549–569. DOI: https://doi.org/10.1146/annurev.ecolsys.38.091206.095601

Renner SS (1989) A Survey of Reproductive Biology in Neotropical Melastomataceae and Memecylaceae. Annals of the Missouri Botanical Garden 76:496. DOI: https://doi.org/10.2307/2399497

Renner SS (1993) Phylogeny and classification of the Melastomataceae and Memecylaceae. Nordic Journal of Botany 13:519–540. DOI: https://doi.org/10.1111/j.1756-1051.1993.tb00096.x

Schiestl FP, Johnson SD (2013) Pollinator-mediated evolution of floral signals. Trends in Ecology & Evolution 28:307–315. DOI: https://doi.org/10.1016/j.tree.2013.01.019

Schneider CA, Rasband WS, Eliceiri KW (2012) NIH Image to ImageJ: 25 years of image analysis. Nature Methods 8:671–675. DOI: https://doi.org/10.1038/nmeth.2089

Trunschke J, Lunau K, Pyke GH, Ren Z-X, Wang H (2021) Flower Colour Evolution and the Evidence of Pollinator-Mediated Selection. Frontiers in Plant Science 12:617851. DOI: https://doi.org/10.3389/fpls.2021.617851

Ulyshen M, Urban‐Mead KR, Dorey JB, Rivers JW (2023) Forests are critically important to global pollinator diversity and enhance pollination in adjacent crops. Biological Reviews 98:1118–1141. DOI: https://doi.org/10.1111/brv.12947

Vallejo-Marín M (2019) Buzz pollination: studying bee vibrations on flowers. New Phytologist 224:1068–1074. DOI: https://doi.org/10.1111/nph.15666

Vallejo-Marín M (2022) How and why do bees buzz? Implications for buzz pollination Bauer U (ed). Journal of Experimental Botany 73:1080–1092. DOI: https://doi.org/10.1093/jxb/erab428

Vallejo-Marín M, Lundgren A (2025) Gradual pollen release in a buzz‐pollinated plant: Investigating pollen presentation theory under bee visitation. Functional Ecology 1365-2435.70189. DOI: https://doi.org/10.1111/1365-2435.70189

Vallejo-Marín M, Pereira Nunes CE, Russell AL (2022) Anther cones increase pollen release in buzz-pollinated Solanum flowers. Evolution 76:931–945. DOI: https://doi.org/10.1111/evo.14485

Vasquez-Castro CA, Morel E, Garcia-Simpson B, Vallejo-Marín M (2025) The fate of pollen in two morphologically contrasting buzz-pollinated Solanum flowers. DOI: https://doi.org/10.26786/1920-7603(2025)836

Weeg MS, Grant JB (2025) Buzz pollination on non-poricidal aspen bluebell flowers. The Southwestern Naturalist 69 DOI: https://doi.org/10.1894/0038-4909-69.2.13

Zhou C, Yu Y, Liu Y, Yang S, Chen Y (2024) Gradual pollen presentation in Vaccinium corymbosum ‘Bluecrop’: an adaptive mechanism to improve pollination efficiency and outcrossing. PeerJ 12:e17273. DOI: https://doi.org/10.7717/peerj.17273

Zuur AF, Ieno EN, Walker NJ, Saveliev AA, Smith GM (2009) Mixed effects models and extensions in ecology with R. Springer, New York. DOI: https://doi.org/10.1007/978-0-387-87458-6