Finding Yourself in an Orchid Position
By: Derek De Witt
Tags: Nature, Flowers, Orchids, Insects

Reproductive Trickery in Flowers

Ophrys umbilicata by Henry Hemming, Flickr

Today we’ll be moving away from the mostly predator/prey relationships that we’ve looked at so far when it comes to mimicry. Instead, we’re going to look a a form of mimicry used to increase the reproductive success of the mimic species. In Season 2, we talked about the mutualistic relationship between many flowers and their pollinators. This story is an example of what happens when the flower ‘cheats’ and denies any potential benefit to the pollinator species.

Why would a pollinator do this work when it receives no benefit? Because the flower in question puts on an elaborate ruse, tricking its helper into thinking it has its own opportunity for reproduction. This is seen frequently with orchids, especially the genus Ophrys. They are sometimes called ‘bee orchids’ because of their mimicry of bees, wasps, and other insects. Because of the ability of many orchids to hybridize easily, the exact number of species in the genus varies depending on the authority doing the classification.

Ophrys scolopax by Luis Nunes Alberto, Wikimedia Commons

This mimicry is similar in many ways to the fireflies from a few weeks ago. The orchid mimics the female of a particular insect to attract males of that species. When the duped insect lands to mate, the male part of the flower attaches a sticky mass of pollen called a pollinium to it. This pollen is then transferred to the female part of another flower when the insect is tricked again. Obviously, the consequences for the dupe are not as severe as the male fireflies, though they do waste large amounts of sperm during these pseudocopulations.

Much like mutualistic pollination relationships, different orchid species have adapted to mimic specific insect species. For example, the mirror orchid, Ophrys speculum, is only pollinated by a species of scoliid wasp, Dasyscolia ciliata. The visual mimicry is excellent, but can be easily over-emphasized by humans, considering that sight is one of the most developed of our five senses. In truth, the visual similarities are important at close range, but are not the key to successful mimicry. The orchids also mimic the texture of their pollinators but the real attractant is chemical in nature. These orchids produce a chemical secretion that is indistinguishable from the natural pheromones of the females of its pollinator species. These chemical signals act as a nearly irresistible lure for the male insects.

Ophrys speculum by Esculapio, Wikimedia Commons

Dasyscolia ciliata by Pietro Niolu, Wikimedia Commons

As before, imagine yourself in the role of the duped organism. You are a male bee or wasp that must mate in a short period of time. You receive a chemical signal from nearby that indicates the presence of a receptive female of your species. Instinctually, you move in to investigate and find something that looks like a female of your species that is producing that scent. You move in to copulate, but find that it is actually a flower, not a female insect. What now? You can be more wary of such signals, but that also increases the chances of false negatives (avoiding the pheromones of an actual female). You need to weigh the various risks of wasting more sperm on a mimic and passing up real mating opportunities.

Duped males have been observed as being more likely to ignore the mimic orchid in future copulation attempts. Timing is also key for the orchid. Its chances at pollination are maximized when it blooms as the reproductive males are active, but the females are not, as there is no competition for their chemical signalling ruse. As it is, only about 10% of all Ophrys individuals are successfully pollinated. However, this is more than enough to maintain the species as a single orchid of the genus produces as many as 12,000 seeds. It also acts as a strong selective pressure on the mimicry of each species. Only the best mimics among the orchids will manage to reproduce and pass on their genes. The mimicry also eliminates the need for the plant to use energy on nectar to attract pollinator species, since it is not providing any benefit for the duped insect.

Next week, we’ll look at another interesting example of mimicry for reproductive purposes. If you like my stories, please like, subscribe, and share them. If you have an idea for a topic for a future season, let me know and if I use it, I’ll give you a shout out in my introductory post.