Ancient DNA reveals surprises

Lead author and University of Otago zoology palaeogenetics laboratory researcher Dr Alex Verry is...
Lead author and University of Otago zoology palaeogenetics laboratory researcher Dr Alex Verry is unlocking some of the secrets of a South Island takahē at Tūhura Otago Museum. PHOTO: LINDA ROBERTSON
The South Island takahē is continuing to provide surprises for scientists.

At the end of the 19th century, it was commonly thought the flightless bird was extinct.

But in 1948, the bird was rediscovered by Invercargill-based physician Geoffrey Orbell, in an isolated valley in the Murchison Mountains, near Te Anau.

On the 75th anniversary of the rediscovery, University of Otago researchers have discovered more surprising information about the bird after mapping its sequenced ancient DNA.

Marred by the impact of humans and past climatic change, the researchers hope the study will enable the past to inform the future by improving conservation management for the species.

The group used palaeogenetic techniques to sequence DNA from South Island takahē and moho (North Island takahē) remains to better understand their evolutionary history, prior to their respective major population bottleneck and extinction.

The researchers found climate change following the end of the last Ice Age and onset of the present warm interglacial period may have led to the local extinction of takahē populations in the Nelson/Tasman region, but it was the arrival of humans to New Zealand about 750 years ago which had the greatest impact.

They were hunted for food and introduced mammals competed for food or preyed on them.

Lead author and University of Otago zoology palaeogenetics laboratory researcher Dr Alex Verry said the extinction of the moho and major loss of genetic diversity within takahē likely occurred by the time of European arrival.

"Takahē went from a large genetically diverse population to a small and inbred one.

"The scale of the genetic bottleneck surprised us, with takahē left with little to no genetic variation.

"We know the bottleneck was large as the genetic lineage that characterises all historic and living takahē is not found in any of our archaeological or subfossil specimens."

Co-author and palaeogenetics laboratory director Dr Nic Rawlence said previous research suggested takahē and moho were distantly related — the result of two separate colonisations of New Zealand by pukeko-like ancestors.

"However, this study shows they descend from a single common ancestor which arrived in Aotearoa approximately 4 million years ago.

"The two takahē species subsequently evolved when the North and South Island landmasses joined around 1.5 million years ago."

The fossil record also suggested takahē preferred edge habitats such as the edges of forests, grasslands and shrubland, where one habitat transitions into another — not the tussock that dominates their home today.

The research illustrated how new technologies and techniques could be used to inform understanding of extinct species.

"The fossil record can, and should, be used to determine the range of suitable habitats and potential translocation sites across the country, based on the preference of prehistoric takahē."