New species can evolve after just two generations
IT was once assumed that forming a separate species took thousands of years.
But the miracle of creating a new kind of animal can take much less time than that, researchers have found.
They observed a population of finches in the process of becoming a species of their own.
The birds evolved from a ‘ cactus finch’, which, fittingly, is a type of Darwin’s finch – so named because they provided the inspiration for On The Origin Of Species.
For many years, the scientists, from Princeton University and Uppsala University in Sweden, followed the population of finches on a tiny Galapagos island called Daphne Major, watching the ‘speciation’ in progress.
The cactus finch, also known as Geospiza conirostris, arrived on the island in 1981, and is native to Espanola, another island 62 miles away.
Peter Grant, professor of ecology at Princeton, said: ‘ We didn’t see him fly in from over the sea, but we noticed him shortly after he arrived. He was so different from the other birds that we knew he did not hatch from an egg on Daphne Major.’ The distance meant that the male was not able to return home to mate with a member of his own species and so chose a mate from among the three species already on Daphne Major.
He bred with a resident medium ground finch of the species Geospiz fortis. But because the offspring of the new bird were so unusual, they found it rather difficult to breed with other birds.
The song of the males, normally used to attract mates, failed to entice females, and the offspring also differed from the resident species in beak size and shape.
So instead, the birds mated mostly among their own lineage.
Within ten years – two generations – the birds began reproducing purely among themselves, the journal Science reports.
By 2010 – some six generations – the flock comprised eight breeding pairs and 36 individuals.
Despite the birds being inbred they seem to be thriving. Explaining the family tree, the authors said the first cactus finch bred with a Geospiz fortis female and just one of the next generation bred with a Geospiz fortis female.
‘But all other matings occurred within this lineage,’ they added. ‘Therefore from generation two onwards the lineage behaved as an independent species.’
The authors said that generations four to six were ‘derived from a single brother-sister mating in generation three’. They added: ‘Despite close inbreeding, members of the lineage experienced high fitness as judged by their reproductive output and high survival.’
They called the new lineage ‘the Big Bird lineage’ as the finches are ‘conspicuously large’. The authors said that ‘reproductive isolation’ – in other words the species only mates with itself – can occur within just three generations instead of hundreds of generations, as previously thought.