Pretty cheats and liars lure researchers False promise <strong>of</strong> sex may save unique orchids 8 <strong>UWA</strong> NEWS <strong>16</strong> <strong>November</strong> 2009 <strong>The</strong> <strong>University</strong> <strong>of</strong> Western Australia
y Sally-Ann Jones Poets have written about unrequited love for centuries – and now chemists and biologists are getting in on the act. An ARC Linkage Project between <strong>UWA</strong>, Kings Park and Botanic Garden, and the Australian National <strong>University</strong> is studying the disappointed love affairs <strong>of</strong> 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. <strong>The</strong> survival <strong>of</strong> ten species <strong>of</strong> Drakaea orchids depends on the wasp that mistakes a flower for a potential mate. Several <strong>of</strong> the orchids, which are unique to a corner <strong>of</strong> the south-west <strong>of</strong> WA, are endangered; one species has already become extinct. More than 150 years ago Charles Darwin wrote his best-selling book <strong>The</strong> 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 <strong>of</strong> the male wasps. It is apt that the research is being done in the 200th year since Darwin’s birth. <strong>UWA</strong> botany graduate and ANU Pr<strong>of</strong>essor 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 <strong>of</strong> his time flying in search <strong>of</strong> a female. Detecting what he thinks is her smell, he follows the odour cue, alights on the female-like structure and attempts to fly <strong>of</strong>f 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 <strong>of</strong> a more responsive female. Whether or not he lands on yet another fake lover, his job is done in ensuring the pollination <strong>of</strong> the orchid because in mounting the flower, he unwittingly transfers its pollen from anther to stigma. <strong>The</strong> orchid is perfectly adapted to look almost exactly like the wingless female, complete with tiny hairs and ‘eyes’. <strong>The</strong> female typically climbs up from the ground for mating, so the male expects to see her on a stalk. Each <strong>of</strong> 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 pheromones, which comprise compounds new to science, can be as little as two hydrogen atoms. “Most plants pay for the service <strong>of</strong> pollination with food, but some don’t,” Pr<strong>of</strong>essor Peakall said. “Instead, they use deception to attract pollinators. Deception costs the plant less. Orchids Dr Gavin Flematti, Pr<strong>of</strong>essor Rod Peakall and Pr<strong>of</strong>essor Emilio Ghisalberti are collaborating to save endangered orchids are the best examples <strong>of</strong> the plant world’s cheats and liars. <strong>The</strong>y’re pollinated by <strong>of</strong>fering the false promise <strong>of</strong> sex. “Drakaea flowers are inconspicuous and have no detectable scent. <strong>The</strong> 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 <strong>of</strong> odour compounds. We pass the compounds over the antenna <strong>of</strong> a wasp and measure the electrical impulses to determine the biologically active compound. “<strong>The</strong> aim is for chemists to make the compound and then try it in the field.” In another project, Pr<strong>of</strong>essor 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 <strong>of</strong> compounds.” Chemist Dr Gavin Flematti in the <strong>UWA</strong> team has already been successful in identifying karrikins, a family <strong>of</strong> compounds that stimulates seed germination in many plants. Its trivial name is derived from the Noongar word ‘karrik’, meaning ‘smoke’. And Chemistry Pr<strong>of</strong>essor Emilio Ghisalberti is excited about the collaboration with Pr<strong>of</strong>essor 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 <strong>of</strong> endangered orchids,” Pr<strong>of</strong>essor Peakall said. <strong>The</strong> <strong>University</strong> <strong>of</strong> Western Australia <strong>UWA</strong> NEWS <strong>16</strong> <strong>November</strong> 2009 9