Detection of signatures of selection in Italian sheep breed

Demographic events such as bottlenecks, genetic drifts, migrations, inbreeding and artificial selection change allele frequencies and combinations in a population. Also natural selection and local adaptation are decisive phenomena in the transmission of favorable genotypes leading to an increase of fitness. In livestock species, genetic diversity has often been assessed by comparing groups with different production aptitude. Contrariwise, the process of adaptive evolution has been frequently neglected because it is difficult to investigate. Sheep breeds, due to their pronounced ability to tolerate different climates and environments, to adapt to different production systems, and to the relative low level of artificial selection they have been subjected to, can represent a good animal model to investigate signatures of selection and adaptation, simultaneously. In this study, in order to detect genomic regions subject to selection a multiple-tests approach was adopted. To provide strong associations and improve power resolution, the canonical discriminant analysis, the fixation index for population differentiation and runs of homozygosity methodologies were implemented in twenty breeds representative of the Italian sheep population. The obtained results revealed the presence of known selection signals harbouring genes involved in milk, meat and wool production and morphological traits (PRL, ABCG2, EDAR, NPR2, MC1R, RXFP2) but also selective sweeps in loci related to sensory system (TAS family, ORs family), circadian rhythm (CLOCK, PER3), skull development (GAB1, NPR3), diseases resistance (DEFB 134, IL6, CDH 26, PRP/PRND) and xenobiotic metabolism (PON1, DPH 6) denoting a strong adaptation to environment. Moreover, new selection signatures were highlighted suggesting several new putative candidate genes for sheep breeds.