“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.
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
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/