Genetic structure and assignment test in five sheep breeds reared in Sicily using microsatellites

A total of 331 individuals from five sheep breeds reared in Sicily (Barbaresca (BAR, n=57), Comisana (COM, n=65), Pinzirita (PIN, n=75), Sarda (SAR, n=64), and Valle del Belice (VdB, n=70)) were analysed to investigate genetic structure and perform an assignment test. A panel of 20 microsatellite markers was used, and a total of 259 alleles were observed. The polymorphic information content (PIC) all over loci was equal to 0.757, showing that the microsatellites panel used was highly informative. Estimates of observed heterozygosity ranged from 0.655 in the BAR breed to 0.751 in the COM breed. The low value of genetic differentiation among breeds (FST=0.048) may indicate that these breeds are not differentiated enough and that they may have common history and breeding practices. Recent migration rates (up to the second generation of migrants) and inbreeding coefficients were estimated using the software BAYESASS+. Four out of the five breeds have not received a significant proportion of migrants (BAR, COM, SAR, and VdB). Only for the PIN breed a recent introgression rate from the VdB breed (7.2%) was found. The posterior distribution of inbreeding coefficient ranged from 0.0321 (COM) to 0.0782 (PIN). The Bayesian assignment test, with the software STRUCTURE, showed that BAR and SAR breeds had a more definite genetic structure (proportion of assignment of 92% and 86.6%, respectively), whereas the lowest assignment value was found in the PIN breed (67.1%). Assigning individuals into populations based on the genetic diversity pattern potentially offers unbiased tools in agriculture for the traceability of animals or animal products, for breed confirmation, or for hybridization detection. Because breed assignment for traceability purposes requires a high certainty, extreme care is needed, in particular for undifferentiated breeds (FST<0.1).