The palm cockatoo, a large species of parrot from Papua New Guinea and Australia, has been dethroned as the common ancestor of the cockatoo family by a new genetic study that has redrawn the family's evolutionary history. Photo: lil moe72SYDNEY: In a study that could dissuade breeders from illegally smuggling parrot eggs, the DNA code of the cockatoo mitochondrial genome has been pieced together, revealing the surprising evolutionary history of these large, native Australasian birds.
While the 21 known species of cockatoos vary significantly in size, plumage colour and bill morphology, those that share similar features are not as closely related as researchers have assumed. The new study, based on DNA sequencing and fossil-based data, has now called for a redraw of the cockatoo family tree.
"The results show that you can't really judge a book by its cover until you open up its DNA and read the code," said lead researcher Nicole White from Murdoch University in Perth. "Previous studies have looked at the birds' behaviour, but that doesn't equate to what you can find in the DNA."
Rethinking the diversification of parrots
The order of parrots (Psittaciformes) to which cockatoos belong is a large and diverse avian group that has been split into three families: Nestoridae (New Zealand parrots), Cacatuidae (cockatoos) and Psittacidae (all remaining parrots).
The initial radiation of the Psittaciformes has been a contentious issue among experts in the past, as molecular approaches to ancestry and information gleaned from the fossil record have yielded different estimates for key dates of divergence.
"In several studies on the temporal evolution of parrots, it was assumed that the initial separation of the Nestoridae from the remaining extant groups of parrots coincided with the separation of New Zealand from Australia about 82 million of years ago in the late Cretaceous," said ornithologist Manuel Schweizer from the Natural History Museum in Bern, Switzerland.
When Australia parted from Antarctica
The relationship between the gang-gang (which has a red head and a black body) and galah (pink head and body with grey wings) was shown to be closer than previously thought Photo: Leo
"This study shows on the basis of independent fossil calibrations and robust analytical techniques that the diversification of modern parrots started much later, in the middle-late Eocene," he added.
Using 40 mitochondrial genomes, including five new cockatoo mitochondrial genomes, together with multiple fossil calibrations, White was able to provide a different estimate for the timing of the radiation of the three parrot families.
Her results, published in Molecular Phylogenetics and Evolution, placed the split of the cockatoos at the time when Australia was drifting west to north-west away from Antarctica, around 40 million years ago.
Colour doesn't mean cousins
By focussing specifically on the diversification of the cockatoo family, White's results also challenged previous assumptions about Cacatuidae lineage, and dethroned the species that was assumed to be the cockatoos' oldest common ancestor - the large, black palm cockatoo from northern tip of the Cape York Peninsula in northern Queensland.
"The general understanding was that the palm cockatoo was the original ancestor that all the other cockatoos stemmed from, but it was actually found to be on a branch of the family tree, as were the other cockatoos," said White, whose results also showed that plumage colour is no indication of close relations.
"The palm cockatoo was found to cluster on the family tree with the white cockatoos, rather than with the other blacks. Likewise the relationship between the gang-gang (which has a red head and a black body) and galah (pink head and body with grey wings) was shown to be closer than previously thought," she said.
Responding to climate change
The results indicated that the 21 species of extant cockatoos began to appear about 10 to 20 million years ago in response to changes in vegetation as the Australian landscape became more arid.
"The Miocene-Pliocene was found to be a significant period for the diversification of cockatoos. A major change in vegetation took place contemporaneously with shrinking of rain forests and an increase in areas of open vegetation in Australia," said Schweizer, whose current research indicates that major lineage diversification events in other Australasian, African and South American parrots took place during the same time period.
"This landscape change may have driven the radiation of cockatoos and promoted the convergent evolution of specific morphological adaptations," he said. "Thus, the middle to late Miocene probably was a significant period for parrot evolution."
Galah (Eolophus roseicapilus) Photo: City parrots
Stopping illegal breeding
White hopes that her research will assist in the conservation of endangered species of cockatoos, such as the white-tailed black-cockatoo, and reduce the instances of illegal shooting and egg smuggling through forensic identification.
"A DNA profiling database is being developed that is identical to what they use in humans. It allows us to not only regulate the bird breeders but also run suspicious material that is seized against the database to determine where it came from," said White.
"We can determine if the offspring from the breeder did breed in captivity, or if it came from an egg smuggled from the wild. It's my understanding that it's hard to breed many of these species in the captivity, so this database can be used for paternity testing."
Animal health experts in Cornwall in the UK have also started taking DNA samples from days-old peregrine falcon chicks to create a similar database to deal with bird dealers engaging in this illegal practice.