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To track human history, just ask the rats

Education

DIRTY rat. Swamp rat. Like a rat up a drainpipe. I couldn’t give a rat’s…

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Rodents are so well known and despised by humans that we’ve incorporated them into many of our best-used derogatory terms.

But researchers at University of Adelaide have capitalised on our intimate relationship with rats. As described in a paper published in the journal PLOS-one, they’ve tracked the migration of pioneers in the Asia Pacific 5000 years ago by analysing ancient rat DNA.

By studying dead rats we’ve had a glimpse at human history

“Whether by accident or deliberately, the first humans to travel across and colonise the Pacific islands took rats with them,” explained Dr Vicki Thomson, who lead the research.

“The island of Flores appears to be the homeland of the Pacific rat.”

Flores exists in the Indonesian archipelago, located between Bali and East Timor. It has a deep fossil record, and has harboured some of the world’s most unusual fauna, including the komodo dragon, dwarfed stegadons and the mysterious species of hominin known as the hobbit (Homo floresiensis).

Vicki and her colleagues found that rat carcasses in Flores contained the highest diversity in their DNA of all the island sites studied across Island South-East Asia and the Pacific.

“We found that populations of the Pacific rat on the island of Flores contain higher levels of diversity in both mitochondrial DNA and allozymes (different enzymes encoded at the same section of the nuclear genome) than any other island,” Vicki wrote in a blog post.

The evidence supports the idea that humans set off from Flores on the very first explorations of the Pacific Islands around 5000 years ago.

“As this rat cannot swim over long distances, we know the arrival of the Pacific rat on an island can be tied back to the appearance of humans, making this rat especially useful for tracking Polynesian migration and trade trips,” wrote Vicki.

Thousand-year-old DNA is not easy to analyse. Luckily, Vicki is based at the largest ancient DNA facility in the Southern Hemisphere, the Australian Centre for Ancient DNA in Adelaide, South Australia.

“Archeologists send us the samples, and we use specialist techniques to piece together and sequence the ancient DNA,” Vicki said.

The results give scientists strong evidence that the cultures and people of modern-day Polynesia were likely strongly influenced by the island of Flores.

“By studying dead rats we’ve had a glimpse at human history,” said Vicki.

Vicki and her colleagues have also used ancient chicken DNA to map human activity across the Pacific.

Vicki presented her research at Fresh Science South Australia 2015.

Fresh Science is a national program that helps early-career researchers find and share their stories of discovery. 

This is a Creative Commons story from The Lead South Australia, a news service providing stories about innovation in South Australia. Please feel free to use the story in any form of media. The story sources are linked in with the copy and all contacts are willing to talk further about the story.

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