Oldest Australian DNA etched from eggshells
Fossilised eggshell from extinct giant birds reveal the oldest DNA traces of Australian fauna ever discovered.
AN INTERNATIONAL TEAM, LED by Charlotte Osken, a biomolecular archaeologist from Murdoch University in Perth, WA, has for the first time successfully extracted DNA from egg remains, including that of a 19,000-year-old emu.
The study’s authors extracted ancient DNA from extinct birds such as the New Zealand's moa and Madagascar's elephant bird — a giant that grew to three metres tall and had eggs bigger than basketballs at 33 cm across.
Duck, owl and emu
The team also successfully extracted DNA from fossilised duck, owl and emu eggs, including the 19,000-year-old emu eggshell from an archaeological site at Tunnel Cave in south-west WA, which is the oldest authenticated DNA sequence ever discovered for Australian fauna, they say.
The team also tried the technique unsuccessfully on a 50,000-year-old fossil eggshell from the extinct giant Australian thunderbird (of the genus Genyornis).
Previously scientists have used eggshells, which are often well preserved, for radiocarbon dating and another dating technique which measures rates of change of amino acids, says co-author and biomolecular scientist Dr Mike Bunce, also from Murdoch University.
But previous efforts were using the wrong technique to get at the DNA, he says.
Slice by slice
The team stained the DNA inside the fossil eggshell using a technique called confocal microscopy, which involves taking optical cross sections of the material. The images showed that the DNA is embedded deep in a calcium carbonate matrix, which may protect it as DNA breaks down under sunlight.
Another major benefit of fossil eggshell DNA is that it tends to have less bacterial and fungal contamination than bone, says Mike. “It may be that it’s a preferable substance for doing genetic sequencing of whole genomes,” he told Australian Geographic.
The paper, published in a recent issue of the journal, the Proceedings of the Royal Society B, represented the “first foray” in the research, he adds, but the technique promises to have wide-ranging consequences for archaeology and palaeontology.
“What we’re excited about is overlying genetics with...radiocarbon [dating] – this will give us a multidisciplinary approach to understanding the past," says Mike.
Never done before
Isotopes are variations in the atomic weights of chemicals and give clues as to what birds ate in the past – for example whether their diet included grass or trees. Dating methods give the time the animals lived, while the new DNA technique could help to differentiate between species, he says.
For example, in New Zealand, before the arrival of humans drove them into extinction, there were many species of the giant, flightless moas, some of the largest birds that ever lived. Extracting their DNA could show what species lived where and help to build up a picture of their evolutionary history.
Dr Jeremy Austin from the Australian Centre for Ancient DNA at the University of Adelaide, says it’s an advance “simply because I think no-one has ever tried to get DNA from fossil eggshells."
But he says that it would still be expensive to attempt to sequence whole genomes of extinct species of birds using egg shells and few labs are in a position to do this at present. “So the justification for sequencing a dodo genome, for example, would need to be pretty good,” he says.