Selection Sweep Analysis of New Zealand Romney and Feral Arapawa Sheep

Comparing diverse strains or breeds of sheep can be used to detect selection sweeps that are contrasting in the traits of interest. The ability to compare “feral” and “improved” sheep allows identification of genetic regions associated with domestication as well as survival without human intervention. To identify genetic regions associated with fitness, disease resistance and dagginess (faecal accumulation in the perineum region) a selection sweep analysis was performed comparing New Zealand Romneys and feral Arapawas using Wright’s fixation index (F_ST). Forty-three Romney and 40 Arapawa sheep were genotyped using the Illumia OvineSNP50-BeadChip and 47,015 single nucleotide polymorphisms passed quality control. The 43 “improved” purebred Romneys, derived from sheep domesticated ~9000 years ago, were representative of their breed. They were also selected for their tendency to accumulate dags. The 40 “feral” Arapawas were once domesticated but were allowed to revert back to their unmanaged state approximately 150 years ago and were subsequently hunted. This breed has low dag accumulation and is resistant to flystrike/myiasis, footrot and internal parasites.  Using a moving window of 5 (WIN5) markers and average F_ST values greater than 0.30 nine genomic regions were identified. These regions were located on chromosomes 2, 10, 13, 17 and X. As expected genes identified included those within the known horns and the agouti regions. Other genes were involved in hair/wool absence/presence and growth, bacterial defence, tuberculosis resistance, anaemia, metabolism and colon cancer. One putative candidate identified was SLMO2 (WIN5 F_ST: 0.37); the mutated form causing slow locomotive behaviour in Drosophila larvae.