Orchids, gorgeous and elegant, are also some of the most deceitful flowers, having evolved sometimes elaborate ruses to lure pollinators.
In a new study of the most brazen of these botanical cheats, the species that entice pollinators with false promises of sex, scientists have discovered that one group of orchids has taken the art of manipulation to shameless heights.
Sexually deceptive orchids, as biologists have long known, look and can even smell so much like a female insect that males will try to mate with the flower in a sometimes vigorous process that can result in pollination. But scientists now report that the tongue orchids of Australia are such thoroughly convincing mimics of female wasps that males not only try to mate with them, but they actually do mate with them — to the point of ejaculation.
“It’s always been described as pseudocopulation,” said Anne Gaskett, a graduate student at Macquarie University in Australia and the lead author of the study. “But it looked like true copulation to me.”
The discovery that orchids can induce such an extreme response is more than just bizarre natural history, because biologists have always assumed that the sexual misrepresentations of orchids were harmless to the duped males, no more than a comical exercise in frustration.
Yet the study, published last month in The American Naturalist, suggests a potentially huge cost to the wasps.
“If males waste all their sperm on orchids,” Ms. Gaskett asked, “what have they got to offer a real female?”
Beyond that, why, scientists asked, would orchids do such an evolutionarily foolish thing? Why would a flower evolve to compromise the ability of its pollinator to reproduce?
So many orchids treat their pollinators so nastily, with false promises of food and sex or the occasional dunking of insect visitors into bucket-shaped petals full of liquid, that naturalists have puzzled over the relationship for more than a century.
Darwin was so consumed by the odd interactions that after “The Origin of Species,” his next book was an entire volume on the subject, “The Various Contrivances by Which Orchids Are Fertilized by Insects.”
In the case of the tongue orchids and their dupe wasps, at least, scientists say they may have deciphered why these flowers abuse their visitors: the treatment of the wasps may, in fact, be very much to the orchids’ advantage.
In wasps, the sex of an individual, male or female, is determined by a peculiar genetic system known as haplodiploidy. In this system, females are produced by an egg from their mother and a sperm from their father. But males have just half of the genetic complement and are produced by females from just an egg, without the aid of a male or a single drop of sperm.
For an orchid that is pollinated just by males, depleting sperm that would be used just to produce females might not be a drawback at all. It could even be a plus, because some female wasps without sufficient sperm tend to produce more sons — or, from the orchid’s perspective, more pollinators.
Increasing the numbers of males, scientists say, could even make males a bit more desperate and less discriminating — another potential advantage for an orchid trying to fool a male into giving the not-quite-right-looking fake female sitting immobile inside its petals a try.
http://www.nytimes.com
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