DNA sheds light on extinct duck’s origins

Building a family tree for two extinct New Zealand bird species has helped Otago scientists uncover their origins, which shows our bird life has more cosmopolitan links than first thought.

The evolutionary history of the now extinct Auckland Islands merganser (Mergus australis) and the Chatham Islands merganser (Mergus milleneri) has been shrouded in mystery.

Study lead author and University of Otago Palaeogenetics Laboratory director Assoc Prof Nic Rawlence said mergansers were migratory riverine and coastal fish-eating ducks.

"These birds are part of a group of ducks that are predominantly only found in the northern hemisphere.

"The only other mergansers known from the southern hemisphere are the critically endangered Brazilian merganser."

He said up until now, it was not known when the ancestors of the extinct mergansers in the New Zealand region or the Brazilian merganser arrived in the southern hemisphere; where they came from in the northern hemisphere; or whether it was one colonisation event into the southern hemisphere or two.

The collaborative research, which involved scientists from Manaaki Whenua Landcare Research, the Museum of New Zealand Te Papa Tongarewa, and the University of Adelaide, used state-of-the-art techniques to extract the DNA from historical specimens of an Auckland Island merganser and a Brazilian merganser.

With that, they were able to reconstruct the species’ "evolutionary tree".

"What we can say is mergansers diverged from their closest living relative about 18million years ago, and from about 14million to 7million years ago they underwent rapid speciation.

"At least 7 million years ago, the ancestors in two independent waves crossed the equator and colonised the New Zealand region and Brazil."

University of Otago Palaeogenetics Laboratory director Assoc Prof Nic Rawlence with a...
University of Otago Palaeogenetics Laboratory director Assoc Prof Nic Rawlence with a taxidermised specimen of an Auckland Islands merganser, which was deemed extinct in 1902. PHOTO: PETER MCINTOSH
Assoc Prof Rawlence said research was now looking at whether there were more than two different species of the bird in New Zealand.

"There are bones on the mainland — are they something different again?

"How many species have we got? When did they diverge in the New Zealand region?"

He said at the time of Polynesian arrival in New Zealand, there would have been mergansers across the North and South Islands, Stewart Island as well as the Auckland Islands and the Chathams.

"Shortly after human arrival, like the moa and the Haast eagle on the mainland, these mergansers went extinct through hunting, habitat destruction through the burning of forests, but also predation from kiore, the Pacific rat, and kurī, the Polynesian dog."

By 1902, due to further predation from cats, pigs and museum collectors, the species was deemed extinct.

Prof Rawlence said the DNA discoveries, so far, were significant.

"It shows an increasing number of New Zealand’s birds don’t hail from Australia, with more cosmopolitan links with Madagascar, Africa, South America, and now the northern hemisphere.