Thursday, August 23, 2007

Orchids and Sex

"a... native orchid trying to outwit a randy male wasp...

Anne Gaskett, a PhD student from Macquarie University in Sydney...
uses advanced colour technology... to understand how five species of native
tongue orchids trick a male wasp into believing he has found a sexual partner.

She says the findings will help to develop environmentally sensitive pest
controls and conserve orchid species.

Ms Gaskett looked at the orchid dupe wasp (Lissopimpla excelsa). And she
says as far as the male is concerned, tongue orchids have "curves in all
the right places".

But the wasp is fooled for only so long.
Her research found that even after just a few exposures to the orchid the
wasp avoids trying to have sex with it.

Ms Gaskett from the Department of Biological Sciences says the orchid must
then enhance its mimicry of the female wasp to continue to attract the male
wasp and pollinate.
"This means only the most persuasive orchids will continue to reproduce,"
she says.
Orchids are the only plant whose flowers trick insects using such sexual
deception. The aim is to convince the insect to 'mate' with them. The
insect accidentally collects pollen on its body, which is then transported
to another flower.

Ms Gaskett says the orchid dupe wasp is attracted to and pollinates five
species of tongue orchid in the genus Cryptostylis.
This is unusual as normally one insect pollinates one species of orchid.
She says this means the five orchid species, which look completely
different to the human eye, must look and feel the same to the male wasp.
Ms Gaskett used a spectrometer to analyse the colours of four of the five
species and a female wasp.
Taking into account factors including the background colour, ambient light
and colour range of the male wasp's receptors, she found the orchid
replicates almost exactly the colours of the female orchid dupe wasp.

She has also found 'hidden shapes' that feel like a female wasp to the
male, including 'love handles' the male wasp grip onto while mating.
Ms Gaskett...
is now studying the perfume of the orchids and testing them on wasp
antennae to look at the role of smell in the seduction process."


Orchids are admired by humans and insects alike, but according to Macquarie University research, one Australian wasp is so enthralled by ‘Orchid Fever' that actually he ejaculates while pollinating orchid flowers.

Australian Tongue orchids lure male insects with counterfeit sex signals that mimic those produced by female insects. Hapless male Orchid Dupe wasps (Lissopimpla excelsa) can't resist mating with the orchid flowers and accidentally become pollen couriers. Until recently, this trick was not thought to harm the reluctant insect Romeos, but biologists Anne Gaskett, Claire Winnick, and Marie Herberstein from Macquarie University, have discovered that the male wasps visiting Tongue orchids waste thousands of sperm on the flowers. "If males waste all their sperm on orchids, what have they got to offer a real female?" asks Gaskett, a PhD student whose research paper on the study was published on Friday in American Naturalist (volume 171, June). "These pollinator species could suffer considerable reproductive costs if orchids inhibit mating opportunities." To investigate this issue the researchers performed a worldwide survey of about 200 insects that are fooled into mating with orchids. Interestingly they found that more than 90 per cent of these duped pollinators were from species with a haplodiploid mating system. Extraordinarily, females from haplodiploid species such as wasps, bees and ants can actually produce offspring without sperm from males.

"Even without mating these females can still reproduce, however all the offspring will be male," says Gaskett. "These consequent extra male wasps could be important pollinators for orchids, and as long as some normal sexual reproduction still occurs, the cost of orchid deception can be mitigated." "Despite the extreme demands they place on their pollinators, Tongue orchids are incredibly successful and have the highest pollination rate ever discovered in a sexually deceptive orchid. And while it's not widely known, Australian orchids are actually global leaders in sexual deception."

Orchids, gorgeous and elegant, are also some of the most deceitful flowers, having evolved sometimes elaborate ruses to lure pollinators.
Orchid Sexual Deceit Provokes Ejaculation (The American Naturalist)
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.


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