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NZ scientists help solve Madagascar genetic mystery

Madagascar, famous for its fictional megalomaniac ring-tailed lemur ruler King Julian, is also home to a much more human mystery: how prehistory settlement of the island off the east coast of Africa happened and gave rise to a genetically distinct group of people (compared to those on the nearby African continent).

Settlers of Indonesian descent

New research from an international research team led by Massey University computational biologist Dr Murray Cox has shown that the island was inhabited only around 1200 years ago. These early inhabitants were approximately 30 women, most of whom, surprisingly, were from Indonesia, 8000 km away. (In the study, approximately 93% of the founding women were calculated as being of Indonesian descent.)

In their published study, the team writes: “Madagascar was one of the last land masses to be reached by people, and despite the island's location just off the east coast of Africa, evidence from genetics, language and culture all attest that it was settled jointly by Africans and, more surprisingly, Indonesians.”

Study focused on mitochondrial DNA

The research team took DNA offered by some 300 Malagasies from three ethnic groups and almost 3000 Indonesians. Focusing on markers handed down in chromosomes through the maternal line, the team used a specially developed computer model to simulate evolution under various parameters to reconstruct the island’s early history. A year and a half of computer time was needed to run the simulations.

In a press release, Dr Cox said it has been known for a long time that there is a really clear Asian signature in the DNA of the Malagasy. “What we’ve done is developed a computer model to find out more about that very early settlement history. Our research suggests that around 30 Indonesian women came to the island about 1200 years ago, around the 9th century AD.”

It is important to note that this study focused on mitochondrial DNA, transmitted only through the mother, so no inference on the number of Indonesian men arriving with the first women can be made.

Theories of settlement

Almost all Malagasy today are related to those 30 founding women. “There has been trading along the Indian Ocean for millennia, and people have assumed that Indonesians settled there as a result of lots of people using this trading route,” he says. “But if it is only 30 individuals, that theory doesn’t make sense. So it appears more likely that this may have been an accidental event – it certainly wasn’t a big, planned movement of people.”

In addition, although the founding population arriving around 830 AD could tie in with the theory that Indonesian trading networks were expanding under the Srivijaya Empire of Sumatra around this time, there is no evidence that women boarded long-distance merchant vessels in Indonesia. Two other theories of settlement offered by the team include that Madagascar was settled as a formal trading colony or ad hoc centre for refugees who had lost land and power during the expansion of the Srivijaya Empire or that the women were on a boat that made an accidental transoceanic voyage. This theory is supported by seafaring simulations using ocean currents and monsoon weather patterns.

Running simulations to discover details of settlement

Dr Cox says simulations are needed to discover the details of the settlement. “Just looking at the DNA itself will tell you some things, like the fact there is an Asian connection, but what it won’t tell you is how many people came and when that happened and what the population size is today. To get that, you have to run simulations to figure out what has happened in the past.

“We simulated under a whole range of different demographic models and found one that matched the actual outcome. That gives us a measurement of what the most likely settlement model is.”

Dr Cox worked with a team that included researchers from the Eijkman Institute in Indonesia, the University of Arizona and the University of Toulouse. The research was published in the Proceedings of the Royal Society B and was funded by the Royal Society of New Zealand through a Rutherford Fellowship.

Useful links

Find out more about DNA sequencing on the Biotechnology Learning Hub.
www.biotechlearn.org.nz/themes/dna_labexternal link

Activity idea

The research discussed in this news article focused on markers handed down in chromosomes through the maternal line. Your students may like to try this activity in which they simulate the passing of traits through three generations. They will also learn about the basic concept of inheritance: that parents pass on genes (within chromosomes) to their children.
Family resemblance traits through generations

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