Dupe: Dasyscolia ciliata, a scoliid wasp, attempting to copulate with a flower of the orchid Ophrys speculum
Mimic: Ophrys speculum, the mirror bee orchid

Pseudocopulation describes behaviors similar to copulation that serve a reproductive function for one or both participants but do not involve actual sexual union between the individuals. It is most generally applied to a pollinator attempting to copulate with a flower. Some flowers mimic a potential female mate visually, but the key stimuli are often chemical and tactile.[1] This form of mimicry in plants is called Pouyannian mimicry.[2]

In orchids

Several species of orchids mimic insects to facilitate pollination, secreting chemicals from glands (osmophores) in the sepals, petals, or labellum, that are indistinguishable from the insect's natural pheromones. The pollinator then has a pollinium attached to its body, which it transfers to the stigma of another flower when it attempts another 'copulation'. Pollinators are often bees, wasps, or flies.[3]

The cost to the pollinating insects might be seen as negligible, but study of Cryptostylis (an Australian orchid) pollinators shows that they may waste large amounts of sperm by ejaculating onto the flower. Thus there could be antagonistic coevolution such that pollinators become better at identifying their own species correctly and orchids become better mimics.[4]

One mechanism is through the use of incentives or rewards. These are beneficial offerings to a pollinator, enticing it to engage with the reward and thus transfer pollen. Flowering plants that do not produce such rewards can instead attract pollinators through mimicry — a form of convergent evolution. Floral mimicry, which has independently evolved in a diverse range of plant species, involves the imitation of other plants or animals, including of coloration, morphology, egg deposition sites, provoking scents, and mating signals.[5] Such plants are called "deceptive plants" as they mimic the characteristics or rewards of other species without providing any benefit to the pollinator.[6][7]

Several orchids (Orchidaceae) make use of floral mimicry. Using sex-based deception, these species imitate female mating signals of certain pollinator species.[8] This results in attempted copulation by males of the pollinator species, facilitating pollen transfer. Bee orchids (Ophrys apifera) and fly orchids (Ophrys insectifera), specifically, utilize flower morphology, coloration, and scent to deceive their respective pollinators. These orchids have evolved traits matching the preferences of specific pollinator niches, leading to adaptive speciation.[9]

Although bee and fly orchids are visual mimics of their pollinators, visual traits are not the only (nor the most important) ones mimicked to increase attraction.[6] Floral odors have been identified as the most prominent way of attracting pollinators, because these odors imitate the sex pheromones of females of the pollinator species.[8] Male pollinators then track these scents over long distances.[6] The proportions of such odor compounds have been found to be varied in different populations of orchids (in a variety of locations), playing a crucial role in attracting specific pollinators at the population level. The evolution of these interactions between plants and pollinators involve natural selection favoring local adaptation, leading to a more precise imitation of the scents produced by local pollinators.[8]

Chemical compounds (more specifically, alkanes and alkenes), while used for sexual deception, are produced in many species of Ophrys, and likely were preadapted for other functions before being co-opted for mimicry.[5] These orchids increased ancestral levels of alkene production to mimic the female pheromones that attract male pollinators, a form of sensory exploitation called a sensory trap.[10]

Although mimetic plants typically receive fewer interactions with pollinators than truly-rewarding plants do, the evolution of sexual deception appears to be linked to benefits associated with mating behavior. Sex-based mimicry results in pollinator fidelity, the continued revisiting of flowers of the same species by a pollinator, as a result of sexual deception. In support of this, sex-based deception in an Australian orchid results in a higher proportions of pollen reaching stigmas than food-based deception. In another study, deception of male pollinators results in a long-distance dispersal of pollen.[6]

See also

References

  1. ^ van der Pijl, Leendert; Dodson, Calaway H. (1966). "Chapter 11: Mimicry and Deception". Orchid Flowers: Their Pollination and Evolution. Coral Gables: University of Miami Press. pp. 129–141. ISBN 0-87024-069-2. OCLC 310489511.
  2. ^ Pasteur, G (1982). "A Classificatory Review of Mimicry Systems". Annual Review of Ecology and Systematics. 13: 169–199. doi:10.1146/annurev.es.13.110182.001125.
  3. ^ Pramanik, Dewi; Dorst, Nemi; Meesters, Niels; Spaans, Marlies; Smets, Erik; Welten, Monique; Gravendeel, Barbara (2020). "Evolution and development of three highly specialized floral structures of bee-pollinated Phalaenopsis species". EvoDevo. 11 (1): 16. doi:10.1186/s13227-020-00160-z. ISSN 2041-9139. PMC 7418404. PMID 32793330.
  4. ^ Gaskett, A. C.; Winnick, C. G.; Herberstein, M. E. (2008). "Orchid Sexual Deceit Provokes Ejaculation". The American Naturalist. 171 (6): E206-12. doi:10.1086/587532. PMID 18433329. S2CID 16443767.
  5. ^ a b Schiestl, Florian P; Cozzolino, Salvatore (2008). "Evolution of sexual mimicry in the orchid subtribe orchidinae: the role of preadaptations in the attraction of male bees as pollinators". BMC Evolutionary Biology. 8 (1): 27. Bibcode:2008BMCEE...8...27S. doi:10.1186/1471-2148-8-27. ISSN 1471-2148. PMC 2267782. PMID 18226206.
  6. ^ a b c d Ellis, Allan G.; Johnson, Steven D. (2010). "Floral Mimicry Enhances Pollen Export: The Evolution of Pollination by Sexual Deceit Outside of the Orchidaceae". The American Naturalist. 176 (5): E143–E151. doi:10.1086/656487. ISSN 0003-0147. PMID 20843263. S2CID 45076899.
  7. ^ Goodrich, Katherine R.; Jürgens, Andreas (2018). "Pollination systems involving floral mimicry of fruit: aspects of their ecology and evolution". New Phytologist. 217 (1): 74–81. doi:10.1111/nph.14821. PMID 28980704.
  8. ^ a b c Vereecken, Nicolas J.; Schiestl, Florian P. (2008-05-27). "The evolution of imperfect floral mimicry". Proceedings of the National Academy of Sciences. 105 (21): 7484–7488. Bibcode:2008PNAS..105.7484V. doi:10.1073/pnas.0800194105. ISSN 0027-8424. PMC 2396721. PMID 18508972.
  9. ^ Schlüter, Philipp M.; Schiestl, Florian P. (2008). "Molecular mechanisms of floral mimicry in orchids". Trends in Plant Science. 13 (5): 228–235. doi:10.1016/j.tplants.2008.02.008. PMID 18424223.
  10. ^ Edwards, David P.; Yu, Douglas W. (2007). "The roles of sensory traps in the origin, maintenance, and breakdown of mutualism". Behavioral Ecology and Sociobiology. 61 (9): 1321–1327. doi:10.1007/s00265-007-0369-3. ISSN 0340-5443. S2CID 43863247.
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