Before they were hunted to the brink of extinction, bison once roamed across North America by the millions in thundering stampedes of rust and auburn fur.

New research decoding their DNA is helping to shed light on how the collapse and slow, scattered return of herds to the landscapes they once dominated has forever changed the mighty species.

The research, published in the journal Science sequenced 160 bison genomes, creating an ancestral roadmap spanning 20,000 years.

Nearly 40 scientists, including many Canadians, contributed to the study. It was led by paleogeneticist Jonas Oppenheimer and the Paleogenomics Lab at the University of California, Santa Cruz, which specializes in researching ancient DNA extracted from fossil remains.

The hope is that the findings will help guide modern conservation efforts — that by mapping the animal’s complicated genetic history, researchers can help the beasts better thrive into the future.

Bison, once highly connected, are now isolated in carefully managed populations. Researchers found that the fragmentation of modern herds challenges their resilience.

"Up until very recently, bison across pretty much the whole extent of North America were very genetically similar, no matter where you pulled them from,” Oppenheimer said in an interview with CBC News.

"That's different from bison today, which are all very different depending on which herd they come from.

“That's the legacy of this huge bottleneck they experienced when they were driven nearly to extinction by humans." The old and the new Sequencing the genomes, complete sets of genetic instructions that serve as the building blocks for life, helped scientists map how the biological diversity of the species has changed over the centuries.

They gathered DNA from both ancient bison bones — ranging from thousands of years old to around 100 — and from living, modern herds. 'The perfect trap': Archeologist reflects on decades at Head-Smashed-In Buffalo Jump Researchers extracted DNA from animals in managed herds scattered across Canada and the United States, including the ones in Elk Island National Park and Wood Buffalo National Park in Alberta, as well as in wild, free-ranging herds in Ronald Lake and Wabasca in the province’s north.

The ancient DNA was sourced from specimens in collections across the United States, Canada and Russia, including those of Parks Canada and the Royal Alberta Museum (RAM) in Edmonton.

Star Blanket Cree Nation welcomes return of bison with new herd In all, researchers sequenced 115 ancient bison genomes and 45 modern, and combined the data with 52 previously sequenced genomes, creating the largest genetic map of the species to date.

Chris Jass, the curator of quaternary (ice age) paleontology at the RAM, said it’s rewarding to see ancient fossils serve modern herd management practices, and called the study a “shining example” of collaboration.

"It is a big part of why we house these collections and why we house them for so long, as these new techniques come along that allow us to look at evolutionary or biological questions in different ways.”Using these samples, researchers were able to track how the bison population’s structure, diversity and genetics were affected by the dramatic declines it experienced.

The slaughter Before colonization, ancient bison moved freely across the continent for thousands of years, interbreeding and maintaining a robust, largely uniform gene pool.

In the late 19th century, the population collapsed from intensive hunting and government campaigns that stripped millions of animals from the plains.

Despite the decline, genetic diversity did not suffer at first because populations had been widespread and uniform up to that point, Oppenheimer said.

The research found a surprising amount of diversity has survived but is now trapped in disparate herds isolated from one another, he added. Modern genetic differentiation mostly survived by chance, remaining ingrained in the DNA of each herd.

“We had assumed that there would be a huge loss,” Oppenheimer said. “As a whole, it doesn't seem like all that much genetic diversity is lost.

“But each particular herd has its own kind of distinct, genetic signature now because of that very recent history.”A 'dramatic split' The study also documented the split between the species, revealing that wood bison and plains bison are substantially distinct.

Wood bison, larger and heavier with a humped profile, are adapted to the northern boreal forests and aspen parklands. Smaller plains bison traditionally roamed the open grasslands and prairies of the Great Plains.

The study shows the two types diverged around 3,000 years ago as changing climates expanded boreal forests.

Later human interventions caused intermixing between the subspecies, most notably when plains bison were moved into Wood Buffalo National Park in the 1920s.

Métis Nation brings bison back for the first time in a century February 25 Duration Greg Wilson, a bison geneticist and wildlife ecologist with Parks Canada, said those results are critical to herd management, showing that the species are distinct and should continue to be managed separately.

While no truly pure wood bison remain, he supports efforts to preserve them as a distinct subspecies.

“Although this split was fairly recent, it's a pretty dramatic split, so this tells us that we really want to try to maintain that.”'More matchmaking' Wilson co-authored the genome study in collaboration with his team at Bison Integrated Genomics, a Genome Canada-funded project to conserve the species through DNA preservation and the establishment of the world's first bison genome biobank.

He said the findings offer conservationists a new tool to reconnect isolated herds and begin the process of reversing the genetic impacts of population loss.

“More matchmaking” could occur among Canada’s isolated herds to reduce the risk of inbreeding and prevent further diversity loss, Wilson said.

Oppenheimer said ancient genomes provide baselines for herd managers to safely restore gene flow across landscapes, helping bison now mostly kept behind gates return to wilderness diversity.

“They maintain that genetic diversity, but there is a chance that different portions of it will get lost if herds are maintained in isolation.”