The Carrion Plants

“Sapromyiophilous” flowers – those which attract carrion and dung flies through mimicry of their food and brood sites – have evolved in many angiosperm families (Ollerton and Raguso, 2006). These species have foul-smelling flowers which are typically brown with purple or reddish blotches and often unusually large, as exemplified by Stapelia gigantea and Rafflesia arnoldii (Barkman et al., 2008).

Stapelia gigantea (left) by World of Succulents and Rafflessia arnoldii (right) by Marian Florcita.

There is now good evidence that the attraction of flies to these flowers depends heavily on the emission of volatiles that are used by flies as cues to locate carrion, faeces and even urine (Shuttleworth and Johnson, 2010). These chemicals emitted by the flowers have been found to structurally resemble those of carrion, and the pollinators could not physically distinguish the two smells (Stensmyr et al., 2002). Attraction of flies through mimicry of their food and brood sites is not confined to angiosperms. There is now good evidence that this occurs among both mosses and fungi, which provides an excellent basis for the study of convergent evolution (Fischer and Vicha, 2003.)

It has been hypothesized that the adaptation of these carrion scents arose from floral scent experimentation (Shuttleworth and Johnson, 2010). As the flowers cannot pick and choose what they mimic, this hypothesis makes sense. With the successful pollination by flies and beetles looking for carrion brooding sites, these chemical odours provided and evolutionary advantage, thus leading to a diverse range of carrion plants. Some of these plants even thermoregulate to further mimic carrion.

Amorphophallus titanum by Smithsonian.

Today there are over 75 identified species of carrion flowers (Stapelia) alone, only belonging to the milkweed family. With at least two other genera in the angiosperms, as well as the mosses and fungi, one can imagine the number of species that employ this mimicry tactic. It is important to remember, though, that although these species are very different, the chemical compounds used in this mimicry are similar or identical (Johnson and Jurgens, 2010). For this reason, these species are a fantastic example and basis for the study of convergent evolution. 

References

Barkman, T.J., Bendiksby, M., Lim, S.H., Salleh, K.M., Nais, J., Madulid, D., Schumacher, T., 2008. Accelerated rates of floral evolution at the upper size limit for flowers. Current Biology 18, 1508–1513.Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/18848446

Fischer, O.A., Vicha, R., 2003. Blowflies (Diptera, Calliphoridae) attracted by Phallus impudicus (Phallaceae) and Stapelia grandiflora (Asclepiadaceae). Biologia 58, 995–998. Retrieved from http://eurekamag.com/research/004/059/004059130.php

Johnson, S. D., Jurgens, A., 2010. Convergent evolution of carrion and faecal scent mimicry in fly-pollinated angiosperm flowers and a stinkhorn fungus. South African Journal of Botany 76, 796-807. Retreived from http://www.sciencedirect.com/science/article/pii/S0254629910001894

Ollerton, J., Raguso, R.A., 2006. The sweet stench of decay. The New Phytologist 172, 382–385. Retrieved from http://onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.2006.01903.x/full

Shuttleworth, A., Johnson, S.D., 2010. The missing stink: sulphur compounds can mediate a shift between fly and wasp pollination systems. Proceedings of the Royal Society B-Biological Sciences 277, 2811–2819. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2981988/

Stensmyr, M.C., Urru, I., Collu, I., Celander, M., Hansson, B.S., Angioy, A.M., 2002. Rotting smell of dead-horse arum florets. Nature 420, 625–626. Retrieved from http://www.nature.com/nature/journal/v420/n6916/abs/420625a.html

Photos

Stapelia gigantea by World of Succulents. http://www.worldofsucculents.com/stapelia

Rafflessia arnoldii by Marian Florcita. https://www.flickr.com/photos/marucs/galleries/

Amorphophallus titanum by Smithsonian. http://botany.si.edu/events/amorphophallus/

The Ophrys Genus

           The Ophrys genus belongs to the Orchidaceae family and contains approximately 30 species. These species are native to Eurasia and North Africa. All have metallic-coloured, hairy flowers that resemble insects (Ophrys 2015). Male insects are lured to the orchid by visual cues and chemical signals. At close range, these signals elicit sexual behaviour in males, whereby the males try to copulate with the flower (Ayasse, et al., 2000). During this process, commonly called pseudocopulation, pollen sacs become attached to the insect’s body and are transferred to the next flowers visited. The fly orchid (O. insectifera) and the bee orchid (O. apifera) are common European species (Ophrys 2015).

Ophrys species are interfertile, meaning they are capable of interbreeding. It is because of this interfertility that reproductive isolation among taxa heavily depends on specific pollinator interaction. Floral odour differences between plant species have often been interpreted as an adaptation to the attraction of distinct pollinators (Dodson et al. 1969). For Ophrys species that are often strongly pollinator limited, selection pressures are imposed by pollinators with different sex pheromone preferences (Ayasse et al. 2000). This pressure is thought to drive floral odour differentiation among orchid populations, ultimately generating adaptive change and species divergence through pollinator shifts (Schiestl and Ayasse 2002).

This genus is a spectacular example of deception and Batesian mimicry in plants. Due to the Ophrys species’ high dependence on specific pollinator interactions, a commensalistic relationship has developed. I can imagine in 50 years the pollinators will have developed a way to identify this deception, however, in the far future it is sure to become a fantastic example of coevolution.

 References

Ayasse, M. et al., 2000. Evolution Of Reproductive Strategies in the Sexually Deceptive Orchid Ophrys sphegodes: How Does Flower-specific Variation of Odor Signals Influence Reproductive Success?. Evolution, 54(6), pp. 1995-2006.http://www.bioone.org/doi/pdf/10.1554/0014-3820%282000%29054%5B1995%3AEORSIT%5D2.0.CO%3B2
Ophrys. 2015. Encyclopædia Britannica Online. Retrieved 22 March, 2015, from http://www.britannica.com/EBchecked/topic/430060/Ophrys

Schiestl, F. P., and M. Ayasse. 2002. Do changes in floral odorcause speciation in sexually deceptive orchids? Plant Sys. Evol.234:111–119. http://www.researchgate.net/publication/225554285_Do_changes_in_floral_odor_cause_speciation_in_sexually_deceptive_orchids

The Plant Kingdom

The plant kingdom, Plantae, is comprised of all land plants and developed between 488.3 million years ago and 443.7 million years ago. It is between these dates that the fossil record contains the miniscule remnants of the first organisms to colonize land (Speer, 1997). In the enormous span of time between then and now, one can imagine the evolutionary experimentation that has taken place. With more than 300,000 known species in the plant kingdom, there is immense competition for nutrients, water, reproductive success, and space (Dickison, 2015). Many species have developed very complex and unique adaptations for dealing with competition. Some of the most interesting are plants that use deception and mimicry to acquire nutrients, attract pollinators, and defend against herbivory.

Before delving into these amazing plants and their unique adaptations, we must distinguish between deception and mimicry as these terms imply different qualities. Deception is often used in the plant kingdom to trick other organisms into providing a service beneficial for the plant (Dafni, 1984). C. K. Sprengel, founder of modern floral biology, recorded in the late 1700s the many deceptive tactics of the genus Orchis, which contains approximately 125 species of orchids. He studied these flowers and found that by appearing similar to a nectar-producing flower or other organism, these plants could attract pollinators and spread pollen without spending energy and resources on actually producing nectar (Dafni, 1984).

Ophrys eleonorae and Ophrys lupercalis, a wild hybrid orchid, whose pollinator, a male solitary bee, is engaged here in pseudocopulation (Pollan, 2011). Photograph: Christian Ziegler/Minden Pictures

          Mimicry is somewhat more complex and can be one of two types. Müllerian mimicry has been defined as when multiple species develop similar traits providing both with an advantage (Barrett, 1987). An example of Müllerian mimicry can be seen between Lantana and Asclepias. Batesian mimicry has been defined as mimicry of one organism or object by another allowing a one-sided advantage to that organism. An example of Batesian mimicry can be found in the genus Lithops (Barrett, 1987).

Mullerian mimicry between Lantana (left) and Asclepias (right). Photographs:Mercewiki (left) and B.T. Wursten (right)

Lithops plants resembling rocks: and example of Batesian mimicry. Photograph: Dysmorodrepanis

            Both deception and mimicry are used in many families and genera of plants around the world. Over the next 11 weeks, I will discuss different techniques of mimicry and deception, how they developed, and the evolutionary advantages these adaptations provide for the taxa they belong to. 










References

Barrett, S. C. H., 1987. Mimicry in Plants. Scientific American, September.255(9).

Dafni, A., 1984. Mimicry and Deception in Pollination. Annual Review of Ecology and Systematics, Volume 15, pp. 259-278.

Dickison, W. C., 2015. Plant, s.l.: Encyclopedia Britannica Online.

Pollan, M., 2011. The weird sex life of orchids. Available at: http://www.theguardian.com/science/2011/oct/09/orchid-sex-botany-ziegler-pollan [Accessed 5 March 2015].
Speer, B. R., 1997. Introduction to the Plantae, Berkeley: University of California Museum of Paleontology.