May 31, 2011

Researchers solve mammoth evolutionary puzzle

    A DNA-based study sheds new light on the complex evolutionary history of the woolly mammoth, suggesting it mated with a completely different and much larger species. Illustration by Raul Martin.

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A DNA-based study sheds new light on the complex evolutionary history of the woolly
mammoth, suggesting it mated with a completely different and much larger species.

The research, which appears in the BioMed Central's open access journal Genome
Biology, found the woolly mammoth, which lived in the cold climate of the Arctic tundra,
interbred with the Columbian mammoth, which preferred the more temperate regions of
North America and was some 25 per cent larger.

"There is a real fascination with the history of mammoths, and this analysis helps to
contextualize its evolution, migration and ecology," said Hendrik Poinar, associate
professor and Canada Research Chair in the departments of Anthropology and Biology
at McMaster.

Poinar and his team at the McMaster Ancient DNA Centre, along with colleagues from
the United States and France, meticulously sequenced the complete mitochondrial
genome of two Columbian mammoths, one found in the Huntington Reservoir in Utah,
the other found near Rawlins, Wyoming. They compared these to the first complete
mitochrondrial genome of an endemic North American woolly mammoth.

"We are talking about two very physically different 'species' here. When glacial times got
nasty, it was likely that woollies moved to the more pleasant conditions of the south,
where they came into contact with the Columbians at some point in their evolutionary
history," he said. "You have roughly 1-million years of separation between the two, with
the Columbian mammoth likely derived from an early migration into North American
approximately 1.5-million years ago, and their woolly counterparts emigrating to North
America some 400,000 years ago."

"We think we may be looking at a genetic hybrid," said Jacob Enk, a graduate student in
the McMaster Ancient DNA Centre. "Living African elephant species hybridize where
their ranges overlap, with the bigger species out-competing the smaller for mates. This
results in mitochondrial genomes from the smaller species showing up in populations of
the larger. Since woollies and Columbians overlapped in time and space, it's not unlikely
that they engaged in similar behaviour and left a similar signal."

The samples used for the analyses date back approximately 12,000 years. All
mammoths became extinct approximately 10,000 years ago except for small isolated
populations on islands off the coast of Siberia and Alaska.

Funding for this study was provided by the Natural Science and Engineering Research
Council and the Canadian Research Chairs program.

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