Poets have written about unrequited love for centuries – and now chemists and biologists are getting in on the act.
An ARC Linkage Project between UWA, Kings Park and Botanic Garden, and the Australian National University is studying the disappointed love affairs of the male Zaspilothynnus wasp.
In fact, they will study the intimate ‘conversations’ that go on, not between wasp pairs, but between male wasps and, in a bizarre interaction, Drakaea orchids that have evolved to look and smell more like female insects than plants.
The survival of ten species of Drakaea orchids depends on the wasp that mistakes a flower for a potential mate.
Several of the orchids, which are unique to a corner of the south-west of WA, are endangered; one species has already become extinct.
More than 150 years ago Charles Darwin wrote his best-selling book The Various Contrivances by which Orchids are Fertilised by Insects, having observed insects visiting the orchids in his own garden in Kent.
Darwin and his son George, who helped,would have applauded this project, in which researchers hope to understand exactly what chemical compounds are involved in the orchids’ deception of the male wasps. It is apt that the research is being done in the 200th year since Darwin’s birth.
UWA botany graduate and ANU Professor Rod Peakall explained that the orchids have everything to gain from the wasps’ misguided attempts at lovemaking and the wasps nothing.
A male Zaspilothynnus wasp spends much of his time flying in search of a female. Detecting what he thinks is her smell, he follows the odour cue, alights on the female-like structure and attempts to fly off with it, only to discover that he’s landed on a flower instead.
Meanwhile, a mechanism near the orchid flower triggers him forwards towards the pollen anthers. Ingloriously covered in yellow pollen, he flies away in search of a more responsive female. Whether or not he lands on yet another fake lover, his job is done in ensuring the pollination of the orchid because in mounting the flower, he unwittingly transfers its pollen from anther to stigma.
The orchid is perfectly adapted to look almost exactly like the wingless female, complete with tiny hairs and ‘eyes’. The female typically climbs up from the ground for mating, so the male expects to see her on a stalk. Each of the orchid species, which are different sizes, has its own amorous wasp species. Each orchid also has its own particular chemical brew with which to attract the corresponding wasp pollinator. And the difference between specific sexual heromones, which comprise compounds new to science, can be as little as two hydrogen atoms.
“Most plants pay for the service of pollination with food, but some don’t,” Professor Peakall said. “ Instead, they use deception to attract pollinators. Deception costs the plant less. Orchids are the best examples of the plant world’s cheats and liars. They’re pollinated by offering the false promise of sex.
“Drakaea flowers are inconspicuous and have no detectable scent. The key for their pollination is sex pheromones plus short-range visual and tactile cues.
“We need to find out what compounds are involved and we’re doing this with gas chromatographic analysis for separation of odour compounds. We pass the compounds over the antenna of a wasp and measure the electrical impulses to determine the biologically active compound.
“The aim is for chemists to make the compound and then try it in the field.”
In another project, Professor Peakall has had success in isolating the compound that attracts thynnine wasp pollinators to Chiloglottis orchids – and the newly discovered compound is named Chiloglottone.
“But the compound involved in the Drakaea’s trickery is not Chiloglottone,” he said.
“Maybe it’s a completely new class of compounds.”
Chemist Dr Gavin Flematti in the UWA team has already been successful in identifying karrikins, a family of compounds that stimulates seed germination in many plants. Its trivial name is derived from the Noongar word ‘karrik’, meaning ‘smoke’.
And Chemistry Professor Emilio Ghisalberti is excited about the collaboration with Professor Peakall. “It’s like detective work,” he said. “You don’t know what you’re going to end up with.”
“This chemical knowledge will help the conservation of endangered orchids,” Professor Peakall said.
• From UWA News, 16 November 2009