Evolutionary genomics and conservation of the endangered Przewalski’s horse. Przewalski horse genomics

Przewalski’s horses (PHs, Equus ferus ssp. przewalski) were discovered in the Asian steppes in the 1870s and represent the last remaining true wild horses. PHs became extinct in the wild in the 1960s, but survived in captivity thanks to major conservation efforts. The current population is still endangered, counting 2,109 individuals, with a quarter in Chinese and Mongolian reintroduction reserves. These horses descend from a founding population of twelve wild-caught PHs, and possibly up to four domesticated individuals. With a stocky build, an erect mane, stripped and short legs, they are phenotypically and behaviorally distinct from domesticated horses (DHs, Equus caballus). Here, we sequenced the complete genomes of eleven PHs representing all founding lineages, and five historical specimens dated to 1878-1929 CE, including the Holotype. These were compared to the hitherto most extensive genome dataset characterized for horses, comprising 21 new genomes. We found that loci showing the most genetic differentiation with DHs were enriched in genes involved in metabolism, cardiac disorders, muscle contraction, reproduction, behavior and signaling pathways. We also show that DH and PH populations split ~45,000 years ago and have remained connected by gene-flow thereafter. Finally, we monitor the genomic impact of ~110 years of captivity, revealing reduced heterozygosity, increased inbreeding, and variable introgression of domestic alleles, ranging from non-detectable to as much as 31.1%. This, together with the identification of ancestry informative markers and corrections to the International Studbook, establishes a framework for evaluating the persistence of genetic variation in future reintroduced populations.