Abstract
BackgroundMerino and Merino-derived sheep breeds have been widely distributed across the world, both as purebred and admixed populations. They represent an economically and historically important genetic resource which over time has been used as the basis for the development of new breeds. In order to examine the genetic influence of Merino in the context of a global collection of domestic sheep breeds, we analyzed genotype data that were obtained with the OvineSNP50 BeadChip (Illumina) for 671 individuals from 37 populations, including a subset of breeds from the Sheep HapMap dataset.ResultsBased on a multi-dimensional scaling analysis, we highlighted four main clusters in this dataset, which corresponded to wild sheep, mouflon, primitive North European breeds and modern sheep (including Merino), respectively. The neighbor-network analysis further differentiated North-European and Mediterranean domestic breeds, with subclusters of Merino and Merino-derived breeds, other Spanish breeds and other Italian breeds. Model-based clustering, migration analysis and haplotype sharing indicated that genetic exchange occurred between archaic populations and also that a more recent Merino-mediated gene flow to several Merino-derived populations around the world took place. The close relationship between Spanish Merino and other Spanish breeds was consistent with an Iberian origin for the Merino breed, with possible earlier contributions from other Mediterranean stocks. The Merino populations from Australia, New Zealand and China were clearly separated from their European ancestors. We observed a genetic substructuring in the Spanish Merino population, which reflects recent herd management practices.ConclusionsOur data suggest that intensive gene flow, founder effects and geographic isolation are the main factors that determined the genetic makeup of current Merino and Merino-derived breeds. To explain how the current Merino and Merino-derived breeds were obtained, we propose a scenario that includes several consecutive migrations of sheep populations that may serve as working hypotheses for subsequent studies.Electronic supplementary materialThe online version of this article (doi:10.1186/s12711-015-0139-z) contains supplementary material, which is available to authorized users.
Highlights
Merino and Merino-derived sheep breeds have been widely distributed across the world, both as purebred and admixed populations
It should be noted that the animals of the Spanish Merino sample were selected to represent two scenarios of how this breed was derived: a current commercial population and the “historical” Spanish Merino population; (2) Spanish breeds with no known Merino influence (Churra, Ojalada, Rasa Aragonesa and Castellana); (3) Italian breeds with no known Merino influence (Massese, Appenninica, Laticauda, Leccese, Comisana and Sardinian White); (4) domestic descendants of primitive sheep
Because selection of SNPs was based on modern domestic breeds, the wild, feral and primitive populations have a lower genetic diversity compared to modern breeds, as suggested by the low values of polymorphic loci (Ppl) and He [See Additional file 1: Table S1], and by the large proportion of loci that fall in frequency bins between 0.8 and 1 [See Additional file 2: Figure S1]
Summary
Merino and Merino-derived sheep breeds have been widely distributed across the world, both as purebred and admixed populations. They represent an economically and historically important genetic resource which over time has been used as the basis for the development of new breeds. During Roman times, Latin authors described different sheep breeds according to their fleece characteristics and celebrated the fine wool of ewes from the Apulia region, in Southern Italy [4]. The Greek author Strabo wrote about the beautiful dark color of the Spanish native breeds. These breeds are believed to have been
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