Five ovine mitochondrial lineages identified from sheep breeds of the near East

Abstract

Archaeozoological evidence indicates that sheep were first domesticated in the Fertile Crescent. To search for DNA sequence diversity arising from previously undetected domestication events, this survey examined nine breeds of sheep from modern-day Turkey and Israel. A total of 2027 bp of mitochondrial DNA (mtDNA) sequence from 197 sheep revealed a total of 85 haplotypes and a high level of genetic diversity. Six individuals carried three haplotypes, which clustered separately from the known ovine mtDNA lineages A, B, and C. Analysis of genetic distance, mismatch distribution, and comparisons with wild sheep confirmed that these represent two additional mtDNA lineages denoted D and E. The two haplogroup E sequences were found to link the previously identified groups A and C. The single haplogroup D sequence branched with the eastern mouflon (Ovis orientalis), urial (O. vignei), and argali (O. ammon) sheep. High sequence diversity (K = 1.86%, haplogroup D and O. orientalis) indicates that the wild progenitor of this domestic lineage remains unresolved. The identification in this study of evidence for additional domestication events adds to the emerging view that sheep were recruited from wild populations multiple times in the same way as for other livestock species such as goat, cattle, and pig.

Figure 1.—

Five mtDNA lineages illustrated with two types of phylogenetic tree. (a) Neighbor-joining tree showing O. aries lineages in relation to wild sheep using cytB sequence (967 bp). Analysis of animals from nine domestic breeds (n = 197) was supplemented with wild Ovis species and a divergent haplotype previously identified from the Karayaka breed (Pedrosa et al. 2005). Additional data on the relationship between wild Ovis species are presented elsewhere (Hiendleder et al. 2002; Bunch et al. 2006). Bootstrap values are indicated on cluster nodes; values in parentheses were taken from a similar tree constructed using the mtCR-cytB data set (2027 bp). (b) Weighted median-joining network showing mt haplotypes. Node size is proportional to haplotype frequency and the mutational differences between haplogroups are proportional to branch length (D shown on branch). The smallest node is representative of one animal.

Figure 2.—

Mismatch distributions within and between clades using the mtCR-cytB data set (2027 bp). Analysis of all 85 haplotypes revealed a tetramodal distribution, which is clear evidence for multiple ovine lineages (a). Haplogroups A, B, and C were analyzed separately (b, c, and d, respectively). Haplogroups were mixed to investigate the relationship between adjacent sequence sets. (e) The distribution following mixing of HA and HD. (f) The distribution following mixing of HC and HE.