The perfume of fruit flies could hold the key to one of the big questions of evolution - how do new species arise?
The conventional model of speciation suggests that new species only evolve when two groups are geographically isolated from one another.
An alternative model that has been hotly debated over the past 50 years is whether new species may arise by natural selection acting to stop breeding between co-existing groups.
University of Queensland and Griffith University evolutionary biologists have been extracting tiny amounts of perfume, or pheromones, which fruit flies use to help them recognise others of their species and to choose mates.
The study, believed to be the first experimental demonstration of the reinforcement of mate recognition by natural selection, has been published in the October 20 issue of the prestigious magazine, Science.
It was conducted by Megan Higgie and Dr Mark Blows of The University of Queensland's Zoology and Entomology Department, and Dr Steve Chenoweth of Griffith University.
Ms Higgie said the new experimental design took advantage of a naturally-occurring pattern in mate recognition.
"We studied two species of Australian native rainforest fruit flies, Drosophila serrata and Drosophila birchii, both of which use pheromones to choose their mates," she said.
"They were a good model because in some parts of Australia they naturally co-exist (are sympatric) but in other parts, they aren't found together in nature (are allopatric).
"Both species are found from Cape York to north of Yeppoon, while only Drosophila serrata is found from Yeppoon to Wollongong.
"We studied the two species in their natural environments and found that the pheromones of Drosophila serrata differed depending on whether individuals were sampled from areas where they co-existed with Drosophila birchii, or from areas where they aren't found together.
"To demonstrate that this naturally-occuring pattern was caused by natural selection on mate recognition, we conducted an evolutionary experiment in which we exposed naturally sympatric and allopatric populations of Drosophila serrata to experimental co-existence with Drosophila birchii for nine generations.
"We predicted that the naturally sympatric populations would not have to evolve, as natural selection had already acted in the wild to allow males and females of each species to choose the correct mates. However, the naturally allopatric populations of Drosophila serrata would have to adapt to co-existence to avoid making mistakes. And that proved exactly the case after nine generations of natural selection."
The researchers were able to measure evolutionary changes by stripping the fruit flies of perfume in a solvent, and studying minute changes to the pheromones using gas chromatography.
Dr Blows said the study of reinforcement of mate recognition by natural selection in the laboratory provided strong evidence that the naturally occurring patterns were due to natural selection on mate recognition to stop interbreeding in the wild.
"Mate recognition is reinforced, so there are fewer mistakes made when choosing mates," he said.
"The experimental design was also a new step forward. We found a natural pattern and reproduced it using an experimental evolutionary approach. Previous work has relied on finding a pattern and simply inferring that the process had occurred.
"Many researchers have found the pattern previously but with long-lived species such as frogs or birds, so it's been harder to demonstrate the process experimentally. Drosophila have a short life span and therefore are more useful for evolutionary studies of this type."
Media: For further information, contact Megan Higgie or Dr Mark Blows at telephone 07 3365 9191, email: mhiggie@zoology.uq.edu.au, or mblows@zoology.uq.edu.au or Jan King at UQ Communications telephone 0413 601 248.
Ms Higgie will attend the Science Writers Festival in Brisbane October 21. She will be available for interview Saturday in room 323, Steele Building, University of Queensland, St Lucia.
ftp site for pix of Megan Higgie and of fruit flies: http://photos.cc.uq.edu.au/PNF:byName:/ScienceWriters/
For more information, email: communications@mailbox.uq.edu.au
