Woolly mammoths mated with Columbian mammoths, a completely different and much larger species

in biology, omics

A new study suggests that woolly mammoth mated with a completely different and much larger species, Columbian mammoth.  This interesting DNA-based finding sheds new light on the complex evolutionary history of the woolly mammoth.

Mammoths were a diverse genus that roamed across Eurasia and North America during the Pleistocene era. In continental North America, at least two highly divergent species have long been recognized, woolly mammoths (Mammuthus primigenius) and Columbian mammoths (M. columbi).

According to the article, 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.

The study was published in the open access journal Genome Biology.

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

 woolly mammoth skeleton 

Skeleton of a Woolly Mammoth in the Brno museum Anthropos. Source:HTO, Wikipedia.

Remains of woolly mammoths have been found across the glacial tundra-steppe of Eurasia and northern North America, while the much physically larger Columbian mammoths inhabited the savannah environments of temperate southern and central North America. The differences between the species have long been considered as unique adaptations to the environments where they evolved.

By piecing together trace fragments of DNA from an 11 thousand year-old Columbian mammoth from Fairview, Utah, the team of Canadian, American and French researchers found that surprisingly the mitochondrial genome from this mammoth was nearly indiscernible from that of its northern woolly counterparts.

Mitochondria contain a small circular DNA with 37 transcript coding genes. Physiologically, mitochondrion is a very important organelle in the cells, as it is responsible for producing most of the energy need of the cells. This is also an important organelle for evolutionary biologists. An individual's mitochondrial genes are not inherited by the same mechanism as nuclear genes. The offspring  carry mother's mitochondrial DNA, and therefore mitochondrial DNA is inherited down the female lineage. Further mitochondrial DNA does not undergo genetic recombination- because the paternal mitochondrial DNA is not represented in the cell. Therefore whole mitochondrial DNA sequence represents a single specificity and unique to the individual. Therefore mitochondrial DNA is preferred to study evolutionary history.

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 mitochondrial 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 more pleasant conditions of the south, where they came into contact with the Columbians at some point in their evolutionary history," he says. "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," says 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 behavior 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.

Source Article: The Complete Columbian mammoth mitogenome suggests interbreeding with woolly mammoths . Jacob Enk, Regis Debruyne, Alison Devault, Christine E King, Todd Treangen, Dennis O'Rourke, Steven L Salzberg, Daniel Fisher, Ross MacPhee and Hendrik Poinar  Genome Biology 2011, 12:R51 doi:10.1186/gb-2011-12-5-r51. Published: 31 May 2011


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Mitochondrial DNA

It is amazing to see that mitochondrial DNA was preserved for these many years. Is there a chance that the Woolly DNA was contaminated with the Columbian mammoth's