Bison bones dating back as far as about 20,000 years show how their history transformed their genetic heritage. By comparing these ancient animals with modern herds, scientists now have a baseline from before their near-disappearance in North America.
The team sequenced the genomes of 115 ancient bison and 45 modern bison from different regions of the continent. The genome contains all of an animal's genetic information. This comparison makes it possible to track connections between populations over a period that cannot be studied using living animals alone.
Pixabay illustrative image
The contrast is striking. In the past, bison populations exchanged genes extensively over long distances. Modern herds appear much more separated from one another, a consequence of the collapse in numbers followed by the establishment of isolated populations.
This break is recent on the scale of the species' history. American bison were pushed to the brink of extinction at the end of the 19th century after once being extremely numerous. The surviving animals then served as the foundation for rebuilding today's herds, with humans organizing their movements.
DNA preserves a record of these interventions. The modern wood bison studied carry, in particular, ancestry from plains bison. Researchers link this to animal transfers carried out in the 1920s, when plains bison were moved to regions occupied by wood bison.
Another finding concerns crossbreeding with domestic cattle. Mating occurred in the past, and its genetic legacy has long fueled discussions about conservation. Yet the analysis shows that many bison do not possess the cattle ancestry sometimes considered to be widespread.
In practical terms, two modern herds can therefore appear to belong to the same species while telling different genetic stories. Some bear the mark of recent relocations, while others have retained more of the characteristics present before the population collapse. Ancient DNA provides the necessary point of comparison for distinguishing between these situations.
This information can help determine how to manage populations without further reducing their diversity. An isolated herd retains only part of the species' diversity. Conversely, moving animals between groups can alter local lineages. Genetic data make it possible to measure these effects before deciding on any potential exchanges.
The collection of genomes thus provides a reference for future restoration programs. Future decisions will be able to compare current herds not only with one another, but also with bison that lived thousands of years before the major upheavals caused by humans. This historical depth now makes it possible to assess more precisely what was lost, preserved, or mixed.