Cheating Orchids (Flower Mimics)

In an intelligently designed world (which ours is not), every flower would offer a reward to its pollinators - you scratch my back and I'll scratch yours (technically called mutualism). Why else would a pollinator be willing to visit flower after flower, inadvertently transferring pollen?

Many orchid flowers violate this sort of reciprocity using a variety of tricks, famously including forming insect mimics to induce insects to attempt to mate with the flowers. I recently read about one trick I hadn't heard of before, at least among orchids (reference below). Two different orchids, Cymbidium insigne and Dendrobium infundibulum, appear to mimic a Rhododendron flower, allowing them to get away without offering the usual nectar reward. The Rhododendron (Rhododendron lyi) and the two orchids have the same range in mountains of northern Thailand. They bloom at the same season and all three are visited by the same bee species (Bombus eximius). The flowers of all three appear quite similar (photos below - they aren't hard for us to tell apart but remember they only have to fool the bee). But only the rhododendron flower produces nectar! No direct proof has been published, but it is likely that both orchids have evolved flowers that are similar to the Rhododendron and have been able to forego the metabolic cost of producing nectar. As long as the Rhododendron flowers are more common than the orchids, this sort of mimicry is thought to be feasible.

The orchids are cheaters and, as long as the Rhododendron and the bees are around and the bees don't catch on, they will no doubt continue their cheating ways. There is risk for the orchids - if the bee or the Rhododendron go extinct the orchids may be doomed as well. These sorts of interdependencies are common in nature, especially in stable warm climates. Evolution does not plan ahead.

It would be interesting to know if a minority of the orchid flowers still make a little nectar (even rare orchids making a very small amount), or if the ability to make nectar has been lost completely (as humans completely lost the ability to make Vitamin C during a period when our ancestors ate mostly fruit). If nectar production is still possible, then the orchids could probably survive loss of the Rhododendron flowers - natural selection to reward pollinators would kick in again and orchids that make more nectar would gradually increase. For we humans, the genes that encode Vitamin C synthesizing enzymes are completely dead (technically called pseudogenes) and without technological intervention we will never make Vitamin C again.

Rhododendron lyi (photo by Marc Colombel)

Dendrobium infundibulum (photo by Marble Branch Farms)

Cymbidium insigne (photo by Simon Pugh-Jones)

Gosta Kjellsson, Finn N. Rasmussen and David Dupuy Journal of Tropical Ecology Vol. 1, No. 4 (Nov., 1985), pp. 289-302