Colourful surprise in cockatoo's tree

Never judge a cockatoo by its colour, say researchers. Image by sunphloSome black cockatoos are more closely related to white cockatoos than we think, according to a new genetic study by Australian researchers.

The findings come from the most detailed ever cockatoo family tree, published in Molecular Phylogenetics and Evolution.

"You can't really judge a book by its cover until you go in and actually read the DNA code," says researcher Nicole White, of Murdoch University in Perth.

Cockatoos may be colourful, charismatic and smart but little has been known about their evolution.

White says the birds, which are spread around the world, belong to the same order as parrots and originated in Australia.

"Australia is the hotbed for cockatoo and parrot evolution," says White who carried out the family tree research as part of her PhD, supervised by Drs Michael Bunce and Peter Spencer.

White and colleagues compared six genes from 16 of the 21 different species of cockatoos we see today.

The amount of DNA sequenced allowed the researchers to not only draw up a family tree, but to use DNA mutations to date when different groups of cockatoos evolved.

Their research found that cockatoos and parrots branched away from each other around 40 million years ago.

Not so black and white

But they also come up with some surprising findings.

While many studies have concluded that there were separate white and black lineages of cockatoos, this study has found otherwise.

It found that the palm cockatoo, a large black cockatoo, was more closely related to white cockatoos than to other black cockatoos.

They also found the red-headed black-bodied gang gang was more closely related to the pink-headed and grey-winged galah.

Some previous research suggested the two were closely related based on the way they flew, but others argued that their colouring was so different they couldn't be so closely related.

Dry life on the Nullarbor made cockatoos go their separate ways

The Nullarbor Plain is daunting not only for people to cross. Genetic research on Australian cockatoos suggests this wide, dry expanse was behind the evolution of white-tailed black cockatoos in the south-west corner of the continent.

White said her DNA study revealed these endangered native birds were closely related to the yellow-tailed black cockatoos that are prevalent on the east coast, and the two species last shared a common ancestor about 1.3 million years ago.

This was about the time the plain became drier, which could have isolated a group in the south-west.

''We believe the aridity of the Nullarbor was the driver of speciation for the white-tailed black cockatoos,'' she said.

Adapting to climate change

The dated family tree also suggests that a changing climate 10 to 20 million years ago resulted in the diversity of cockatoos we see today.

"The Australian landscape changed quite radically," says White. "A more arid climate started to develop."

She says cockatoos responded to the changing vegetation, for example, by developing beaks there were able to eat the hard fruit of eucalypt trees.

"For the birds to be able to survive, they had to be able to adapt to be able to eat these new food resources," says White.

As humans replaced native forests with other trees such as fruit and nut orchards, some cockatoos have also adapted to feed on these, she says.

"They're actually learning how to crawl under fences to get into the nut orchards," says White.

White says the new DNA sequences can also be used to identify when endangered birds are being trafficked.