In an interesting report by researchers in the Cell Press Journal and as republished by Science Daily on Sept. 24, the complete genomes of eleven Przewalski horses – as well as founding lineages and five museum specimens over 100 years old – have now been comprehensively sequenced. These results were then compared to the genomes of 28 domesticated horses. This thorough study was undertaken to gather detailed data from endangered horses of the past to the present time.
Przewalski horses are generally acknowledged as the world’s last truly wild horses. They lived in the wilds of Mongolia and China until around 1960 when the last remaining Przewalski horses lost their freedom. Only a single captive population still existed, descended from around a dozen wild-caught Przewalski horses and possibly four domesticated animals. With intense conservation efforts, the Przewalskis now number just over 2,000 horses. Of those, about one-quarter live in reintroduction sanctuaries.
According to Ludovic Orlando of the University of Copenhagen’s Natural History Museum of Denmark, the researchers used a unique method in their studies by not only charting current genomic diversity of the Przewalskis, but also scrutinizing century-old diversities found in museum specimens. In this way, researchers were able to evaluate the genomic impact of over 100 years of captivity in a critically endangered animal.
As a matter of fact, we also show that very early in captivity – in the early 1900s – domestic horses contributed significantly to some lineages of the Przewalski’s horse pedigree. It implies that not all of the surviving Przewalski’s lineages represent the gene pool of wild horses equally.
The data gathered by the researchers may solve a debate about horses’ evolution that concerns the wild horse and domestic horse connection. They conclude that the Przewalski horse and domesticated horse lineages were linked by gene flow for a long time after their divergence over 45,000 years ago, and their offspring were often mixtures of wild and domestic horses even after domestication. They discovered that the most notable genetic differences in domesticated and wild horses were in “metabolism, cardiac disorders, muscle contraction, reproduction, behavior and signaling pathways.”
Perhaps the major finding by the researchers shows the last 100-plus years of captivity left Przewalski horses with lower genetic diversity and more inbreeding. There is even evidence that there is a “significant introduction of genes from domesticated individuals.”
There is good news, however. Orlando says,
Even though Przewalski’s horses went through an extreme demographic collapse, the population seems to recover, and is still genetically diverse. There is, thus, hope for [other] endangered populations, fighting similar demographic issues.
The researchers, bolstered by their conclusive results about the importance of DNA evidence in regards to animal domestication, they plan to examine more wild and domestic horses with an eventual goal of reconstructing the history of 5,500 years of horse domestication.