Sheep is thought to be one of the first domesticated livestock species. Animal domestication has been widely investigated in order to better understand the phenotypic and genetic changes of animals caused by human activities. However the process where domestic animals become feral is still poorly understood. Since domestication is known as the process where protection offered by domestic habitat suppresses the original environmental adaptation, feralization is like its reverse: the animals re-start to fit natural life while human artificial selections were no longer dominant. Semi-feralization has an extensive impact over diverse phenotypic traits of sheep. By acquiring features similar with their wild ancestors, semi-feral sheep were able to re-gain fitness in frequent contact with wild surroundings and rare human interventions.

Here, whole-genome sequencing of 99 sheep were performed and a primary genetic divergence between two heterogeneous populations in the Tibetan Plateau was identified, including one semi-feral lineage. Selective sweep and candidate gene analysis revealed the local adaptations of these sheep associated with sensory perception, muscle strength, eating habit, mating process and social behavior. In particular, a horn-related gene RXFP2 showed signs of rapid evolution in the semi-feral breeds specifically. A unique haplotype and repressed horn-related-tissue expressions of RXFP2 were correlated with higher horn length, as well as spiral and horizontally extended horn shape. This study provided a novel insight into processes of semi-feralization of domestic animals and can be referred to understanding the genetic basis underlying growth of horns in goat and cattle.

By Liu Qiuyue
liuqiuyue@caas.cn