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BackgroundAnimal domestication has been extensively studied, but the process of feralization remains poorly understood.ResultsHere, we performed whole-genome sequencing of 99 sheep and identified a primary genetic divergence between 2 heterogeneous populations in the Tibetan Plateau, including 1 semi-feral lineage. Selective sweep and candidate gene analysis revealed local adaptations of these sheep associated with sensory perception, muscle strength, eating habit, mating process, and aggressive behavior. In particular, a horn-related gene, RXFP2, showed signs of rapid evolution specifically in the semi-feral breeds. A unique haplotype and repressed horn-related tissue expression of RXFP2 were correlated with higher horn length, as well as spiral and horizontally extended horn shape.ConclusionsSemi-feralization has an extensive impact on diverse phenotypic traits of sheep. By acquiring features like those of their wild ancestors, semi-feral sheep were able to regain fitness while in frequent contact with wild surroundings and rare human interventions. This study provides a new insight into the evolution of domestic animals when human interventions are no longer dominant.

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The bone morphogenetic protein receptor IB (BMPR-IB) was studied as a candidate gene for the prolificacy of sheep. Nine pairs of primers (P1-P9) were designed to detect single nucleotide polymorphisms (SNPs) of exons 1-4 and 6-10 of the BMPR-IB gene in both high (Small Tail Han and Hu sheep) and low prolificacy breeds (Texel and Chinese Merino sheep) by polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP). Only the products amplified by primers P2, P5, P6, P7, P8 and P9 displayed polymorphisms. The present study identified 22 SNPs in partial coding regions of ovine BMPR-IB, in which 20 SNPs were reported for the first time. In total of the 22 mutations, 18 DNA variations were originated from the Hu breed, three were found in the Small Tail Han breed (two of them were found in other sheep breeds), three in the Chinese Merino breed, and none in the Texel breed. These results preliminarily demonstrated that BMPR-IB is a major gene affecting the hyperprolificacy in Small Tail Han and Hu sheep, and could be used as a molecular genetic marker for early auxiliary selection for hyperprolificacy in sheep.