Genetic Distinctiveness of the Herdwick Sheep Breed and Two Other Locally Adapted Hill Breeds of the UK

There is considerable interest in locally adapted breeds of livestock as reservoirs of genetic diversity that may provide important fitness traits for future use in agriculture. In marginal areas, these animals contribute to food security and extract value from land unsuitable for other systems of farming. In England, close to 50% of the national sheep flock is farmed on grassland designated as disadvantaged areas for agricultural production. Many of these areas are in the uplands, where some native breeds of sheep continue to be commercially farmed only in highly localised geographical regions to which they are adapted. This study focuses on three of these breeds, selected for their adaptation to near identical environments and their geographical concentration in regions close to one another. Our objective has been to use retrotyping, microsatellites and single nucleotide polymorphisms to explore the origins of the breeds and whether, despite their similar adaptations and proximity, they are genetically distinctive. We find the three breeds each have a surprisingly different pattern of retrovirus insertions into their genomes compared with one another and with other UK breeds. Uniquely, there is a high incidence of the R0 retrotype in the Herdwick population, characteristic of a primitive genome found previously in very few breeds worldwide and none in the UK mainland. The Herdwick and Rough Fells carry two rare retroviral insertion events, common only in Texels, suggesting sheep populations in the northern uplands have a historical association with the original pin-tail sheep of Texel Island. Microsatellite data and analyses of SNPs associated with RXFP2 (horn traits) and PRLR (reproductive performance traits) also distinguished the three breeds. Significantly, an SNP linked to TMEM154, a locus controlling susceptibility to infection by Maedi-Visna, indicated that all three native hill breeds have a lower than average risk of infection to the lentivirus.人们对地方适应性畜禽品种抱有极大兴趣，这类品种作为遗传多样性的储备库，可为未来农业生产提供关键的适应性性状。在边际农业区域中，这类畜禽不仅保障了当地粮食安全，还能从其他养殖系统无法利用的土地中获取经济价值。在英国，全国近50%的绵羊群养殖在被划定为农业生产弱势区域的草地上。其中多数区域位于高地地带，部分本土绵羊品种仅能在与其适配的高度局限的地理区域内进行商业化养殖。本研究聚焦其中三个品种，这些品种因适配近乎一致的环境，且地理分布区域彼此邻近而被选中。本研究的目标是通过逆转录分型（retrotyping）、微卫星标记（microsatellites）与单核苷酸多态性（single nucleotide polymorphisms，SNP）技术，探究这些品种的起源，以及尽管它们具有相似的适应性且地理邻近，是否仍具备遗传特异性。研究发现，与其他英国绵羊品种相比，这三个品种各自的基因组内逆转录病毒插入模式均存在显著差异。尤为特别的是，赫德威克羊（Herdwick）群体中R0逆转录型的检出率极高，该类型对应此前仅在全球极少数品种中发现的原始基因组特征，且英国本土此前从未见报道。赫德威克羊与罗夫费尔羊（Rough Fells）携带两种罕见的逆转录病毒插入事件，这类插入仅在特塞尔羊（Texel）中常见，这表明北部高地的绵羊种群与特塞尔岛的原始针尾绵羊存在历史渊源。微卫星数据以及与RXFP2（调控角性状）、PRLR（调控繁殖性能性状）相关的单核苷酸多态性分析，同样可区分这三个绵羊品种。尤为重要的是，与TMEM154（调控梅迪-维斯纳病毒（Maedi-Visna）感染易感性的基因位点）相关的单核苷酸多态性分析显示，这三种本土山地绵羊品种感染该慢病毒（lentivirus）的风险均低于平均水平。