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Sex and the single mammoth

Doug O'Harra
Royal BC Museum illustration

Like an airliner packed to the overheads with sun-seeking, romance-starved Alaskans on a lusty spring break Hawaiian hunk hunt, a population of the Far North's venerable woolly mammoths may have ventured far south during the height of the Ice Age -- where they were wooed, mounted and ultimately impregnated by a slew of their much larger cousins, the subglacial Columbian mammoths.

The first complete mitochondrial genome of the Columbian mammoth -- a 13-foot-tall, 11-ton critter given to browsing mid-continent forests -- has uncovered the genetic wild oats, so to speak, of the smaller, scrappier, hairier and perhaps, one wonders, much hornier woolly mammoth.

The result? At least two Columbian mammoths that lived about 12,000 years ago in Utah and Wyoming had more than few woollies hiding in their genetic attics.

"Though limited, our data suggest that the two species interbred at some point in their evolutionary histories," an international team of 10 scientists concluded in a paper published last month in the journal of Genome Biology.

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

"We are talking about two very physically different 'species' here," he said. "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."

Columbian mammoths -- the common prehistoric New World elephants whose tusks litter the La Brea Tar Pits and other Lower 48 digs -- evolved from an earlier mammoth species that arrived in North America an estimated 1.5 million years ago. The 8-ton woolly mammoths, whose ubiqitous remains are known as Alaska's official state fossil, ambled across the 1,000-mile-wide Bering Land Bridge from Asia about 400,000 years ago and thrived in Alaska and northern Canada until about 10,000 years ago.

Until now, scientists doubted the two species ever had much contact, since they lived in different habitats, following different habits and diets. The Columbians were 25 percent larger and inhabited what is now Mexico, Texas, California and other contiguous states. The Woollies, on the other hand, grazed an ecosystem that no longer exists ­-- a windswept, arid plain that reached from Asia across Alaska into the Yukon, what retired Fairbanks paleontologist R. Dale Guthrie named the "Mammoth Steppe."

Now one sort of boggles at a different vision, one where the two species somehow found each other, possibly in a zone where their habitats overlapped -- what's known as an ecotone -- and commenced to disturb America's prehistoric glades with some unlikely fur-flying, elephantine congress.

"We think we may be looking at a genetic hybrid," said co-author 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 scientists said that mammoth genetic research has previously focused on almost entirely on woolly mammoths, making it difficult to put the woollies in context with other Ice Age elephants. So Poinar and his colleagues decided to target the Columbians for new clues into mammoth ancestry.

"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," the story explained. "They compared these to the first complete mitochrondrial genome of an endemic North American woolly mammoth."

The findings strongly suggest a complicated interbreeding of the two species and their subsequent hybrids, possibly over many generations. That such a thing happened at all might offer insight into the breakdown of the Ice Age world and the subsequent extinction of most of the large North American mammals.

"The precise mode and setting of genetic interchange between WMs and CMs are elusive, and therefore all hypotheses explaining our observations warrant testing," the scientists wrote.

"Interbreeding between extinct late Pleistocene taxa -- especially keystone herbivores like mammoths -- could serve as an indicator of major ecological events, including those surrounding the megafaunal extinctions."

Contact Doug O'Harra at doug(at)alaskadispatch.com