Scientists have produced the first comparison of DNA sequences between Przewalski’s horse and the domestic horse.
Przewalski’s horses (Equus ferus ssp. przewalskii) in Askania Nova, a biosphere reserve located in Ukraine. Image credit: 2B Patchett / CC BY-SA 2.0.
Przewalski’s horses were discovered in the Asian steppes of Mongolia and China in the 1870s and represent the last remaining true wild horses.
The species became extinct in the wild in the 1960s but survived in captivity, thanks to major conservation efforts.
The current population is still endangered, with just 2,109 individuals, one-quarter of which are in Chinese and Mongolian reintroduction reserves.
Now, an international team of scientists has sequenced the complete genomes of eleven Przewalski’s horses (Equus ferus ssp. przewalskii), representing all founding lineages, and five museum specimens dated to 1878-1929 CE.
The team compared these genomes to the genomes of 28 domesticated horses to provide a detailed look at the endangered animals, both past and present. The results were published online this week in the journal Current Biology.
“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,” said Dr Ludovic Orlando of the University of Copenhagen’s Natural History Museum, Denmark, who is the senior author on the study.
“That way we could assess the genetic impact of more than 100 years of captivity in what used to be a critically endangered animal.”
The genomic evidence helps to solve a long-standing debate in horse evolution, regarding the relationships between wild and domestic horses (Equus caballus).
“We show that populations of Przewalski’s horses and domesticated horses split about 45,000 years ago and have remained connected by gene-flow thereafter,” the researchers said. “Their populations continued to mix even after humans started to domesticate the horse about 5,500 years ago.”
The team found the greatest genetic differences between domesticated and wild horses in genes involved in metabolism, cardiac disorders, muscle contraction, reproduction, behavior, and signaling pathways.
The findings also show that the last 110 years of captivity have left a mark on the Przewalski’s horses, in the form of lower genetic diversity, increased inbreeding, and, in some cases, the significant introduction of genes from domesticated individuals.
In the most extreme cases, about a quarter of the genomes of Przewalski’s horses consisted of gene variants inherited from domesticated horses.
“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,” Dr Orlando concluded.
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Clio Der Sarkissian et al. Evolutionary Genomics and Conservation of the Endangered Przewalski’s Horse. Current Biology, published online September 24, 2015; doi: 10.1016/j.cub.2015.08.032
