October 23, 2012
Ancient New Zealanders Get Their Complete Mitochondrial Genome Sequenced
April Flowers for redOrbit.com — Your University Online
A research team from the University of Otago has achieved landmark results by sequencing the complete mitochondrial genome for members of what was likely to be one of the first groups of Polynesians to settle New Zealand. The results of this study, published online in the Proceedings of the National Academy of Sciences, have revealed a surprising degree of genetic variation among these pioneering voyagers.
Similar DNA detective work with samples from various modern and ancient Polynesian populations will be much easier due to the breakthrough work from the Otago team. Researchers might now be able to clear up competing theories about the pathways taken in the great Polynesian migration across the Pacific to New Zealand.
The team successfully mapped complete mitochondrial genomes of four of the Rangitane iwi (tribe) tupuna (ancestors) who were buried at a large village on Marlborough's Wairau Bar more than 700 years ago. The Wairau Bar site was first excavated over 70 years ago and is one of the most important archaeological sites in New Zealand because of the incredible range of material found there. Some of the first generations of people who settled New Zealand occupied this fourteenth century village, which has provided the first material evidence that New Zealand was settled by East Polynesians.
Mitochondrial DNA (mtDNA) is only inherited through the mother's side and can be used to trace maternal lineages. This provides insights into ancient origins and migration routes, according to Professor Lisa Matisoo-Smith.
"We found that three of the four individuals had no recent maternal ancestor in common, indicating that these pioneers were not simply from one tight-knit kin group, but instead included families that were not directly maternally related. This gives a fascinating new glimpse into the social structure of the first New Zealanders and others taking part in the final phases of the great Polynesian migration across the Pacific."
The four genomes shared two unique genetic markers found in modern Maori. They also featured several previously unidentified Polynesian genetic markers. At least one of the settlers, rather surprisingly, also carried a genetic mutation associated with insulin resistance, which leads to Type 2 diabetes.
"Overall, our results indicate that there is likely to be significant mtDNA variation among New Zealand's first settlers. However, a lack of genetic diversity has previously been characterized in modern-day Maori and this was thought to reflect uniformity in the founding population."
"It may be rather that later decimation caused by European diseases was an important factor, or perhaps there is actually still much more genetic variation today that remains to be discovered. Possibly, it may have been missed due to most previous work only focusing on a small portion of the mitochondrial genome rather than complete analyses like ours."
The team used Otago's state-of-the-art ancient DNA research facilities, applying similar techniques that were used recently to sequence the Neanderthal genome by other studies.
"We are very excited to be the first researchers to successfully sequence complete mitochondrial genomes from ancient Polynesian samples. Until the advent of next generation sequencing techniques, the highly degraded state of DNA in human remains of this age has not allowed such genomes to be sequenced," she says.
Work can now begin to gather and sequence other ancient and modern DNA samples from Pacific Islands to search for the same genetic markers that the team has identified in New Zealand's founding population.
"If such research is successful, this may help identify the specific island homelands of the initial canoes that arrived in Aotearoa/New Zealand 700 years ago," she says.