Genetic diversity and population structure of Sicilian sheep breeds using microsatellite markers

Abstract

a b s t r a c tGenetic diversity studies in domestic animals aim at evaluating genetic variation within and across breeds mainly for conservation purposes. In Sicily, dairy sheep production represents an important resource for hilly and mountain areas economy. Their milk is used for the production of traditional raw milk cheeses, sometimes protected designation of origin (PDO) cheeses. In some cases, the quality of these products is linked to a specific breed, i.e. mono-breed labelled cheeses and it is therefore important to be able to distinguish the milk of a breed from that of others, in order to guarantee both the consumer and the breed itself. In order to investigate the genetic structure and to perform an assignment test, a total of 331 individuals (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 using a panel of 20 microsatellite markers. A total of 259 alleles were observed with average polymorphic information content equal to 0.76, showing that the microsatellites panel used was highly informative. Estimates of observed heterozygosity ranged from 0.65 in the BAR breed to 0.75 in the COM breed. The low value of genetic differentiation among breeds (F st = 0.049) may indicate that these breeds are little differentiated probably due to common history and breeding practices. The low F is and F it values indicated low level of inbreeding within and among breeds. The unrooted neighbor-joining dendrogram obtained from the Reynold's genetic distances, and factorial correspondence analysis revealed a separation between BAR and the other sheep breeds. Recent migration rates were estimated, showing that four out of the five breeds have not received a significant proportion of migrants. Only for the PIN breed a recent introgression rate from the VDB breed (7.2%) was observed. The Bayesian assignment test 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%). Our results indicated high genetic variability, low inbreeding and low genetic differentiation, except for BAR breed, and were in accordance with geographical location, history, and breeding practices. The low robustness of the assignment test makes it unfeasible for traceability purposes, due to the high level of admixture, in particular for COM, PIN and VDB.

Genetic diversity of locally adapted sheep from Pantanal region of Mato Grosso do Sul

“…The population parameters observed in the present study were also higher than those observed in other sheep breeds, both locally adapted, and exotic, from Spain (Calvo et al, 2011), India (Arora et al, 2011), Italy (Lasagna et al, 2011), and Cuba (Álvarez et al, 2012). Tolone et al (2012) found very similar results when analyzing five Sicilian sheep breeds with 20 microsatellites (average of 10.95 alleles per locus for the native sheep Pinzirita). Baumung et al (2006) reported an average of 15 alleles, when 25 microsatellite markers were genotyped in 11 Austrian breeds.…”

“…This result may be due to the small sample population (15 individuals), and due to the population being consolidated with planned genetic crosses established from breeding programs. Several studies using locally adapted or native breeds confirmed that these breeds have more number of loci in HWE when compared to more specialized breeds (McManus et al, 2010;Paiva et al, 2011a;Tolone et al, 2012).…”

Parentage verification of Valle del Belice dairy sheep using multiplex microsatellite panel

“…Within Sicilian flocks, rams and ewes are reared together; therefore mating with close relatives could be quite frequent. Moreover, the reduced or absent exchange of rams between different flocks may have induced the development of a substructure within this population (Tolone et al, 2012). This could be more frequent where the assessment of parentage is not carried out (Pariset et al, 2003).…”

Genetic diversity of Colombian sheep by microsatellite markers

“…Within the most visited farms in the investigation, inbreeding resulted from the lack of control in mating between animals which led to a lot of mating between related individuals, thus, eventually leading to the heterozygous reduction in the populations (Martínez et al, 2010 On the other hand most of production systems in the country have one or two sires to mate with all the females of the herd, which could reduce significantly the genetic diversity in the populations and contribute to the reduction of heterozygous individuals in the population (Tolone et al, 2012).…”