The 'founder effect' theory, a controversial idea among biologists, says that speciation occurs suddenly due to a small influx of colonists founding new populations, in the process creating many new gene combinations and losing many others, in what is known as a 'genetic revolution'.
But according to the team's new evidence from fieldwork and computer modelling, the theory doesn't apply to island birds, and the way in which populations change their genetic diversity is a result of successive colonisation events and long-term genetic drift.
"Our results indicate that speciation in island birds occurs gradually, not suddenly as a result of island colonisation through founder effects," said Dr Sonya Clegg of Imperial College London.
In order to carry out the work, Dr Clegg and her collaborators visited a series of islands through the south west Pacific.
Dr Clegg said: "The result is exciting because this is the first time the theory has been tested using natural populations. Previous tests have used artificially introduced ones, which don't tell you much about how real biodiversity evolves. It's obvious that genetic changes can occur if a single pair of individuals founds a population, but the question is whether that really happens. Our results suggest that it doesn't."
The scientists tested the founder effect model in an unusual island bird species, the Silvereye (Zosterops lateralis), which has colonised a series of islands in the south west Pacific from the Australian mainland during the last 200 years.
The Silvereye's pattern of colonisation there was originally used to support the founder effect model, first proposed by Ernst Mayr
Contact: Tom Miller
Imperial College London