European Bison Origins Mystery Solved: A Hybrid Species Identified

Researchers have solved the mystery surrounding the origins of European bison, finding that a now-extinct hybrid species was the source. This hybrid species formed when the ancestor of European wisent bison — called steppe bison — mated with the ancestors of what are now modern-day cattle: Aurochs. This hybrid species paved the way for Europe's wisent bison, though the hybrids themselves eventually died out, leaving a gap and, for the longest while, a big mystery.

The discovery was recently detailed in a study newly published in Nature. The researchers point toward the existence of two distinct types of bison, the American bison and the European bison. While researchers have long been able to trace the history of the American bison, its European counterpart has remained a big source of speculation.

As far as had been determined, the mysterious wisent bison has no Pleistocene-era fossil record, instead seemingly appearing from nowhere about 12,000 years ago. European bison do share some close similarities with their American counterparts, though, at least at the DNA level. However, researchers say the mitochondrial DNA also shows that the wisent bison are ultimately closer to modern day cattle.

Another part of the larger mystery was the obvious inclusion of two distinct types of bison in cave artwork. This indicated that there may have been a second variety of bison alive during that time that had thus far eluded modern researchers. Searching for this possible unknown bison that once roamed Europe led to the discovery of the hybrid species.

In explaining how they went on to probe this hybridization, the researchers said:

...we used target enrichment and high-throughput methods to sequence ∼10,000 genome-wide bovine single-nucleotide polymorphisms (SNPs) from nine members of CladeX, an ancient (>55 kyr) and a historical (1911 AD) wisent specimen and two steppe bison (30 and >50 kyr)

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The nuclear and mitochondrial analyses together suggest that the common ancestor of the wisent and CladeX mitochondrial lineages originated from asymmetrical hybridization (or sustained introgression) between male steppe bison and female aurochs.