Academic journal article Genetics

The Evolutionary Origin and Genetic Makeup of Domestic Horses

Academic journal article Genetics

The Evolutionary Origin and Genetic Makeup of Domestic Horses

Article excerpt

THE history of the domestication of the horse remains enigmatic in several aspects due to the absence of clear morphological and osteological differences between wild and early domestic individuals, but also due to the scarcity of paleontological records from some key periods, especially the one preceding the earliest evidence of domestication. This evidence is given by the ~5500-year-old archaeological site of Botai (modern-day Kazakhstan) (Outram et al. 2009), at a considerable spatial and temporal distance from the Anatolian domestication centers for sheep and goats (Zeder et al. 2006). Unlike other ungulates, horses were not only used as a source of meat and milk, but their stamina and speed also revolutionized warfare and transportation. This also promoted cultural exchange, including the spread of IndoEuropean languages, religions, science, and art (Kelekna 2009; Anthony 2010). With the introduction of the horse collar and horseshoes in agriculture, the horse was increasingly used for tilling soils, incrementing farmland productivity in medieval Europe, and remains today an essential asset to the agriculture of the least-developed countries.

Human activities have conversely influenced, directly or indirectly, the evolution of horses, causing a drastic reduction of truly wild populations. After the extinction of the Tarpan horse in 1909, which populated Eastern Europe a few centuries ago, the only surviving wild relative is the endangered Przewalski's horse. The latter was described in the Asian steppes in the 1870s, and overhunted to such an extent that it was, not >90 years later, officially declared extinct in the wild by the International Union for Conservation Nature. The Przewalski's horse survived in captivity due to successful conservation programs, which raised a stock of 12-16 captive founders to >2000 individuals, one-quarter of which are in Mongolian and Chinese reintroduction reserves (King et al. 2015). Once "extinct in the wild," its current conservation status has been upgraded to "endangered." In parallel to the extinction of wild populations, human-driven management, in particular through selection, has dramatically influenced the recent history of domestic horses, developing multiple breeds with a wide range of phenotypic peculiarities. Although some horse breeds, such as the Thoroughbred racing horses, are still extremely popular, a significant part of this great diversity is currently endangered. According to the Food and Agricultural Organization of the United Nations (FAO 2015), 87 horse breeds are already extinct and among the remaining 905, almost a quarter are categorized as at risk.

The population structure resulting from selective breeding is characterized by high interbreed and low intrabreed genetic diversity (McCue et al. 2012), and reflected by a huge array of morphological and behavioral traits (Figure 1). The height at withers, for example, extends from 70 cm in miniature Falabella horses to over 2 m in Shire and Percheron horses; an intraspecific range that is only exceeded by height variation in domestic dogs (Brooks et al. 2010). Domestic horses also exhibit striking variation in coat coloration, including the bay or bay-dun wild-type phenotypes, other basic colors like chestnut and black, as well as dilution (e.g., cream and silver), and spotting patterns (e.g., leopard complex, tobiano, and sabino) (Ludwig et al. 2009). Horse locomotion has also been recurrently selected, including their ability to perform alternate gaits, such as four-beat, lateral, or diagonal ambling. These alternate gaits come in addition to the three natural gaits (walk, trot, and gallop), and are known to increase the comfort of the rider and positively influence racing performance (Andersson etal. 2012; Promerová et al. 2014). Due to pleiotropic and/or epistatic effects, some of the traits selected in domestic breeds are, however, indirectly associated with congenital diseases (Bellone et al. …

Search by... Author
Show... All Results Primary Sources Peer-reviewed

Oops!

An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.