Tuesday, February 9, 2010

Greed in the Plant Kingdom

Angiosperms (flowering plants) are the current unit in Bio 122. I now have  a number to back up a concept I already knew: Most flowering species (approximately 80%) rely on a living agent to serve as pollinator. A mutualistic relationship is the norm, with insects or hummingbirds pollinating flowers in return for the reward of sweet nectar. These flowers tend to be brightly colored and sweet-smelling. Many of those dependent upon insects for pollination have markings (invisible to humans without ultraviolet light) known as “nectar guides” to indicate a direct route to the prize. My favorite flowers would all fall into this category. Artifice? Definitely. But also a quid pro quo.

Imagine my surprise to learn that just as the human world is rife with deceit driven by greed, so is the plant kingdom. Orchid lovers may be familiar with my first tale, but  it was news to me.

Tale Number One: Male wasps of the species Campsoscolia ciliata often attempt to copulate with the flowers of the Mediterranean orchid Ophrys speculum. During the encounter, a sac of pollen becomes glued to the insect’s body. In frustration, he heads off to another flower for a second try and there deposits the pollen. No reward. Just frustration and eventual exhaustion. Dozens of species of orchid engage in this form of sexual trickery. The Aragon region of Spain even promotes this subterfuge as a tourist attraction. The deception was long thought to be a purely visual one — the orange bristles around the flower’s largest petal apparently resemble the anatomy of the female wasp. The current belief, however, is that the flower emits a chemical scent similar to that of a sexually receptive female wasp. There are comprehensive treatises on the subject if you want to learn more.

Tale Number Two: Scent is also part of the equation for pollination by blow-flies (scavengers of carrion and dung, and layers of eggs, which hatch into maggots found in these materials.) Flowers attracting such pollinators are often reddish and fleshy and smell like decomposing flesh. While laying her eggs on such a flower, the female blow-fly becomes dusted with pollen that she then carries to another blossom. When her eggs eventually hatch, there is no meat to eat, and her offspring die! I wonder how bad these flowers smell. Has anyone ever planted them around a picnic area?

Pollination (plant sex) is all about survival. That’s a fact. Sometimes it involves two species with a mutual benefit, but oftentimes not. Just as the human world has Bernie Madoffs, it can be “all about me” in the plant world as well. Think about that the next time you admire an exotic orchid (or, depending on your taste, a flower that smells like a rotting corpse.) 

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