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Betrayal: Non-rewarding Orchids Use Devious Means to Attract Pollinators

October 3, 2016

Did you know that the exotic and beautiful orchids that we so admire and value practice betrayal on a regular basis? It sounds laughable, but it’s true. Orchids are almost exclusively dependent on animal pollinators for their sexual reproduction, but a full third of the species in this extremely large plant family are non-rewarding. Pollinators aren’t just paying a social call when they land on an orchid or other flower, they visit with the expectation of a reward in the form of nectar or some other needed substance; however, when they visit an orchid, they walk or fly away unrewarded — victims of these deceptive plants.

It may seem as though I am attributing some malice or ill-intent on the part of the orchids, and obviously this is not true. Orchids are plants, not sentient beings. They have evolved their deceptive practices in order to survive and surely don’t deserve our derision for that deception. Instead, if you consider it, orchids have evolved some rather amazing ways to attract pollinators without having any reward with which to entice them.

There are many ways in which non-rewarding orchids attract pollinators, and I’d like to present just a few of the most common to give you an idea of how amazing these plants really are. These methods are floral mimicry, the magnet species effect, and brood site mimicry.

Floral Mimicry

Orchids Trichocentrum ascendens and Rossioglossum ampliatum (left and right); Malpighiaceae (center). Photo credit: Papadopulos et al. 2013.

Orchids Trichocentrum ascendens and Rossioglossum ampliatum (left and right); Malpighiaceae (center). Photo credit: Papadopulos et al. 2013.

The relationship between pollinators and plants is generally a win-win. The pollinators visit plants to get a reward, such as nectar, and in return they carry the plants’ pollen to other plants giving a chance for cross-pollination to occur. In floral mimicry, non-rewarding orchids take advantage of this existing relationship between pollinators and the reward-producing plants by mimicking the appearance of the flowers of the reward-producing plants, especially their color.

A recent study by Alexander S. T. Papadopulos, et al., on neotropical orchids presents a good example of this type of mimicry. The yellow flowers of the orchid species Trichocentrum ascendens and Rossioglossum ampliatum are so close in hue to the yellow flowers of neighboring Malpighiaceae plants, that “a visiting bee cannot differentiate between flowers of the two groups with respect to flower color” (2013).  So, while buzzing from yellow flower to yellow flower, the bees are likely to visit both the orchids and the rewarding flowers, not realizing the difference between them until it’s too late.

Magnet Species Effect

Orchids also score visits from pollinating insects simply by growing in proximity to populations of “magnet” species, or rewarding plants. Just as a

This orchid, Anacamptis morio, takes advantage of pollinators visiting neighboring rewarding plants. Photo credit: Didier Desouens.

This orchid, Anacamptis morio, takes advantage of pollinators visiting neighboring rewarding plants. Photo credit: Didier Desouens.

magnet attracts iron shavings, a magnet species attracts pollinators. It’s not a magnetic attraction per say, really it’s the lure of a reward that draws pollinators to the area. By growing in the same location, orchids get to benefit from the same pollinators who chances are will stop by to check them out while they are in the area. This magnet species effect can be seen in a study done in 2001 by S. D. Johnson, et al., on the island of Öland, Sweden. In this study, the pollination success of the non-rewarding orchid species Anacamptis morio is shown to significantly increase when grown near to two rewarding plant species, Geum rivale and Allium schoenoprasum (2003). The bumblebees that are there to get the nectar from the rewarding plants tend to visit the orchids too.

Brood Site Mimicry

Hoverflies are duped into visiting these Epipactis veratrifolia by the distress pheromones they release. Photo credit: Hans Stieglitz.

Hoverflies are duped into visiting these Epipactis veratrifolia by the distress pheromones they release. Photo credit: Hans Stieglitz.

In brood site mimicry, orchids mimic conditions that would make an optimal site for pollinators to lay their eggs. An excellent example of this can be seen in the orchid species Epipactis veratrifoli which grows in the eastern Himalayas. This species has evolved an amazing way of attracting its only pollinators, female hoverflies seeking the perfect location to lay their eggs (Jin et al. 2014)Since hoverfly young survive on a diet of aphids, the flowers of this fantastic mimic actually release the same pheromones that aphids do when in distress (Jin et al. 2014)What female hoverfly ready to unload her precious cargo could resist the scent of aphids in trouble?

This species of orchids actually isn’t quite as deceptive as some of the other species of non-rewarding orchids. Aphids can be found on their blooms, especially early in the flowering season, and at least some of the hatching hoverflies will find their expected food source. Unfortunately, there’s not enough to feed them all. Some will surely starve to death, but at least there is a reward for some!

I hope that the next time you see a beautiful orchid, you’ll look at it with a new appreciation for its amazing evolution. Orchids may be deceptive, but their ability to attract pollinators without being able to offer a reward is an amazing adaptation. There is still much to be studied to truly understand why so many orchids have evolved to be non-rewarding instead of evolving a reward for their pollinators. However, even without our complete understanding, orchids truly deserve all of the admiration and value we place on them.

References

Gumbert A, Kunze J (2001) Colour similarity to rewarding model plants affects pollination in a food deceptive orchid, Orchis boryi. Biol J Linn Soc 72.3:419-433.

Jersakova J, Johnson SD, Kindlmann P (2006) Mechanisms and evolution of deceptive pollination in orchids. Biol Rev Camb Philos Soc 81.2:219-235.

Jin X, Ren Z, Xu S, Wang H, Li D, & Li Z (2014) The evolution of floral deception in epipactis veratrifolia (orchidaceae): From indirect defense to pollination. BMC Plant Biol 14.1:63. doi:http://dx.doi.org/10.1186/1471-2229-14-63.

Johnson SD, Peter CI, Nilsson LA, Aagren J (2003) Pollination success in a deceptive orchid is enhanced by co-occurring rewarding magnet plants. Ecol 84.11:2919-2927.

Papadopulos AST, Powell MP, Pupulin F, Warner J, Hawkins JA, Salamin N, Chittka L, Williams NH, Whitten WM, Loader D, Valente LM, Chase MW, Savolainen V (2013) Convergent evolution of floral signals underlies the success of Neotropical orchids.  Proc Biol Sci R Soc 280.1765:20130960.

Photo Credits

Top:  from Papadopulos AST, Powell MP, Pupulin F, Warner J, Hawkins JA, Salamin N, Chittka L, Williams NH, Whitten WM, Loader D, Valente LM, Chase MW, Savolainen V (2013) Convergent evolution of floral signals underlies the success of Neotropical orchids.  Proc Biol Sci R Soc 280.1765:20130960.

Middle: by Didier Desouens http://commons.wikimedia.org/wiki/File:Anacamptis_Fleur_global.jpg

Bottom: by Hans Stieglitz http://commons.wikimedia.org/wiki/File:Epipactis_veratrifolia.jpg

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