Humans began domesticating horses 5,000 years ago. However, genetic analysis recently revealed that wild horses, also known as Przewalski's horses, have remained connected to their domesticated relatives by a common gene flow, even after diverging from one another some 45,000 years ago.
Wild horses once lived throughout the Asian steppes of Mongolia and China, but from the 1870s to the 1960s their freedom to roam was slowly and steadily restricted and they were threatened with extinction. One captive population of Przewalski's horses remained, and thanks to conservation efforts, a total of 2,000 individuals are still alive today.
To better understand how wild horses have evolved, researchers compared the genetics of 11 wild horse genomes to 28 domesticated horses.
"The novelty of our approach is to have not only surveyed the present-day genomic diversity of Przewalski's horses, but also to monitor their past genomic diversity, leveraging on museum specimens," Ludovic Orlando, from the University of Copenhagen's Natural History Museum of Denmark, said in a news release. "That way we could assess the genetic impact of more than 100 years of captivity in what used to be a critically endangered animal."
Now, researchers have a better understanding of the relationships between wild and domestic horses.
"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," Orlando added. "It implies that not all of the surviving Przewalski's lineages represent the gene pool of wild horses equally."
There are still many differences between the two species. For example, the genes that control metabolism, heart disorders, muscle control, reproduction, behavior and signaling pathways vary among wild and domesticated horses, researchers noted. After being placed in captivity, the Przewalski horses also have lower genetic diversity, increased inbreeding and introduction of genes from domesticated species.
"Even though Przewalski's horses went through an extreme demographic collapse, the population seems to recover, and is still genetically diverse," Orlando said. "There is, thus, hope for [other] endangered populations fighting similar demographic issues."
Their research was recently published in the Cell Press journal Current Biology.
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