Genomic signatures of adaptive introgression from European mouflon into domestic sheep

Mario Barbato,Monica Pirastru,Pablo Orozco-Terwengel,Paolo Mereu,James Kijas,Frank Hailer,Raffaele Mazza,Michael W Bruford,Pierangela Cabras

doi:10.1038/s41598-017-07382-7

Abstract

Mouflon (Ovis aries musimon) became extinct from mainland Europe after the Neolithic, but remnant populations from the Mediterranean islands of Corsica and Sardinia have been used for reintroductions across Europe since the 19th-century. Mouflon x sheep hybrids are larger-bodied than mouflon, potentially showing increased male reproductive success, but little is known about genomic levels of admixture, or about the adaptive significance of introgression between resident mouflon and local sheep breeds. Here we analysed Ovine medium-density SNP array genotypes of 92 mouflon from six geographic regions, along with data from 330 individuals of 16 domestic sheep breeds. We found lower levels of genetic diversity in mouflon than in domestic sheep, consistent with past bottlenecks in mouflon. Introgression signals were bidirectional and affected most mouflon and sheep populations, being strongest in one Sardinian mouflon population. Developing and using a novel approach to identify chromosomal regions with consistent introgression signals, we infer adaptive introgression from mouflon to domestic sheep related to immunity mechanisms, but not in the opposite direction. Further, we infer that Soay and Sarda sheep carry introgressed mouflon alleles involved in bitter taste perception and/or innate immunity. Our results illustrate the potential for adaptive introgression even among recently diverged populations.

Highlights

Introgression is increasingly documented as a potentially adaptive evolutionary force[1], with recent developments in high-throughput genotyping and sequencing facilitating the detection of even small genomic regions that have been passed on from one taxon to another[2]
We found that putatively introgressed genomic regions in mouflon were not systematically enriched for particular gene ontology (GO) terms, while introgressed regions in domestic sheep were enriched for genes related to innate immunity and bitter taste recognition
Our results indicate that this population, which so far has been used as a representative of Sardinian mouflon at large[21, 55] is not representative of pure European mouflon, and that other mouflon population we studied may be more suitable as reference populations

Summary

Introduction

Introgression is increasingly documented as a potentially adaptive evolutionary force[1], with recent developments in high-throughput genotyping and sequencing facilitating the detection of even small genomic regions that have been passed on from one taxon to another[2]. The European mouflon (O. aries musimon) is the only wild ovine currently occurring in Europe. The European mouflon, together with the Cypriot mouflon (O. orientalis ophion) and some primitive domestic breeds present in Northern Europe such as the Soay and Spael sheep are considered remnants from the first wave of domestication[8]. Mouflon x sheep hybrids tend to be larger than mouflon[16], and larger-bodied mouflon males have higher reproductive success[17]. Despite these records of mouflon x sheep admixture, and sexual selection might act to enhance introgression into mouflon, little information is available on the scale, impact and adaptive significance of admixture between mouflon and domestic sheep

Methods

Results

Discussion

Conclusion