Historical Museum Specimens, Ancient DNA Studies, and the Origin of Przewalski’s Horses

The debate surrounding the “purity” of Przewalski’s horses (described scientifically in 1881, native to Mongolia and China) is a legendary subject in the literature of captive propagation and endangered species management and reintroduction. As is often the case, strongly held opinions are based on data that are subject to diverse interpretations. The similarity and confirmation in coat color between the Przewalski’s horse and western European cave paintings has long supported the consideration that the Przewalski’s horse is the primitive wild horse. The discovery in 1960 that Przewalski’s horses had more chromosomes than domestic horses further bolstered this assertion. However, recent genetic information suggests that the Przewalski’s horse has far too close an affinity with domestic horses to be the primitive horse. But these findings, based on mitochondrial DNA, are themselves disputed by other studies.

Clearly, the Przewalski’s horse has had a complex evolutionary history and though it is genetically distinct, may nonetheless have experienced repeated and sustained gene flow from either the predecessors of domestic horses or early domestic horses themselves. Fortunately, this is a testable hypothesis, and since potentially much is at stake, the opportunity to utilize new methods and develop scientific insights to this question poses a significant opportunity in conservation research.

Formal research efforts by the Genetics Division of the San Diego Zoo's CRES center to address questions concerning the origin of this unique species are now underway with the arrival of two international visitors. Dr. Natalia Abramson, curator of mammals at the Zoological Museum of St. Petersburg, recently arrived from Russia with bone fragments from ancient populations of horses, including Przewalski’s horses. Dr. Gila Kahila Bar-Gal from the Koret School of Veterinary Medicine, Hebrew University of Jerusalem, recently arrived from Israel to share her knowledge about the rigorous methods involved in extracting “ancient” DNA. Dr. Bar-Gal’s previous work included, among a diverse array of studies, DNA analysis of the Dead Sea Scrolls.

This international collaboration will enhance understanding of the genetic background of Przewalski’s horses and shed light on their enigmatic origins. Are they the same as the horses depicted in the cave paintings or are they of more recent form, derived from an isolated population of the lineage that now includes domestic horses? Shedding light on this paleo-DNA mystery is the aim of this exciting collaboration and has direct connections to current management of captive and reintroduced populations of Przewalski’s horses. Data generated from specimens of Przewalski’s horses collected prior to the establishment of captive populations will be compared to data on the current captive population, domestic horses, Pleistocene horse samples, and samples from recent geological periods prior and shortly after the time of domestication. These comparative data will help establish the extent of gene flow from domestic horse ancestors and/or domestic horses into Przewalski’s horse populations.

The genetic variability of Przewalski’s horses in the wild, prior to their decline and extinction in nature, provides a crucial basis for structuring efforts in captive management and reintroduction. Once fraught with controversy, a knowledge-based rationale for management actions can now be developed. All of this nearly a century after the first breeding of Przewalski’s horses in captivity and with the help of technology that could not have been imagined a short decade ago!

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CRES News Archive: Experts Meet to Finalize Horse DNA Mapping