The Consequences of Gene Flow between Wild and Domestic Populations during Livestock Evolution

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Generally speaking, modern domestic species are actively prevented from interbreeding with wild populations. The few exceptions to this rule involve the deliberate generation of novel hybrid pets such as those involving domestic and wild cat species. This practice of incorporating wild species in breeding lines is strongly discouraged amongst livestock species since the introduction of genes from wild populations reduces productivity and the degree of tameness in the hybrids. In the recent past, however, husbandry practices were far less restrictive. Recent ethnographic and genetic analyses have revealed that interbreeding between numerous species of domestic and wild species was, in fact, the rule and not a rare exception.While gene flow from wild populations can be detrimental, it can also have a positive impact on livestock populations. For example, by decreasing the risks associated with inbreeding and by introducing genetic variation that allowed for rapid adaptation to novel environments. Adaptive gene flow therefore potentially played an important role during the spread of domestic animals across the world. This is especially true of pigs since geographically and genetically differentiated populations of wild boar are present across Eurasia and adapted to a wide variety of climates and environments; thus providing raw material that could have been absorbed by arriving domestic pigs. In fact, we demonstrated that gene flow between wild and domestic pigs was common and that it began immediately following the introduction of pigs to Europe from the Near East where they were initially domesticated. Despite this gene flow, pigs in Europe maintained their integrity as domestic animals by retaining their morphological and behavioural distinctiveness, suggesting that though some wild boar genomic variation was incorporated into domestic stocks, many wild boar genetic variants were actively expunged. Here, we will determine whether some wild genetic variants were preferentially expunged and whether some were preferentially incorporated into domestic populations. Ultimately, this project will reveal not only the genomic basis for domestication, but also how domestic pigs adapted to novel environments, by identifying specific genomic regions that were rapidly incorporated, and which ones were resisted during gene flow. To do so, we will assess the DNA preservation of more than 1,000 ancient pigs and wild boar from Eastern and Western Eurasia over the past 10,000 years, and then sequence the entire genomes of the best preserved specimens. Armed with this data, we will establish the spatial and temporal differences in the proportion and genomic location of the incorporation of wild boar genes into domestic stocks. The results will allow not only an unprecedented understanding of the origins of domestic animals, they will also have important ramifications for the conservation of endangered wild boar populations and for pig breeders and consumers of pork for whom the authenticity of domestic and wild meat is crucial.