Mitochondrial DNA D-Loop diversity and evolutionary relationship of wild Punjab Urial sheep (Ovis vignei punjabiensis) with closely related taxa

Abstract

The taxonomy and systematics of wild sheep is complex with several classifications and revisions proposed on the basis of morphology, geographic distribution and chromosome number. Punjab Urial (O. vignei punjabiensis), an important sub-species of O. vignei is distributed in Pakistan and is classified under vulnerable category. The taxonomic status of this sub-species remains uncertain and the present study is an attempt to assess its mitochondrial DNA diversity and evolutionary relationship with closely related taxa. Analysis of mitochondrial DNA D-Loop of O. vignei punjabiensis revealed wide variations in the number and pattern of tandem repeats as compared to other Moufloniform wild sheep. With the exception of tandem repeat regions, a total of 117 sequences coveringan overlapping region of 748bp from nine wild and domestic sheep populations were analyzed. The nucleotide and haplotype diversity was low to moderate within different sheep populations and Punjab Urial sheep exhibiting a mean of 0.0043 and 0.829 respectively. The average pairwise differences within population varied from 0.67 (O. musimon) to 23.69 (Kachi) while the average differences between Urial sheep and other Moufloniform wild sheep populations was high indicating the distinctness of O. vignei. Bayesian and maximum likelihood phylogeny clearly established the divide between the lineages of O. vignei and O. orientalis populations. Also, the average pairwise differences between O. vignei bochariensis and O. vignei punjabiensis were significantly higher (P<0.01) despite both the populations being classified as sub-species of Urial type sheep. To compare O. vignei punjabiensis with Argaliform and Pachyceriform wild sheep, pairwise FST between populations were utilized to perform principal components analysis (PCA). PCA revealed clustering of Asiatic (O. orientalis), European (O. musimon) and Captive Mouflon type sheep together, while O. nivicola and O. canadensis clustered separately. O. ammon and O. vignei bochariensis were observed to be clustering together while O. vignei punjabiensis was located distinctly. The tests for selective neutrality indicated purifying selection in Punjab Urial sheep while Asiatic Mouflon appears to have experienced a strong population bottleneck in the recent past. Considering the declining population trend and loss in genetic diversity due to possible genetic bottleneck events, there is an urgent need to implement strong conservation measures for O. vignei punjabiensis in the region.