Mitogenomic analysis of the genus Pseudois: Evidence of adaptive evolution of morphological variation in the ATP synthase genes

Sichuan Key Laboratory of Conservation Biology on Endangered Wildlife, Key Laboratory of Bio-resources and Eco-environment (Ministry of Education), College of Life Sciences, Sichuan University, Chengdu, Sichuan 610064, PR China.
Mitochondrion (Impact Factor: 3.25). 07/2012; 12(5):500-5. DOI: 10.1016/j.mito.2012.07.107
Source: PubMed


The genus Pseudois includes two variable taxa, blue sheep (Pseudois nayaur) and dwarf blue sheep (Pseudois schaeferi), that exhibit notable geographic variation in morphology and ecological niche, suggesting the potential for significant adaptive differentiation between these two goats. Blue sheep are broadly distributed in the Tibetan Plateau and peripheral mountains through Central Asia, while dwarf blue sheep are only found in the gorges of the upper Yangtze River (Jinsha River) near Batang county, Sichuan province and adjacent mountains. Although they are all adapted to high altitude environments, endangered dwarf blue sheep show unique morphological variation and niche shifts compared to blue sheep. Mitochondria play important roles in oxygen usage and energy metabolism. The energetically demanding lifestyles of these high altitude species may have altered the selective regimes on mitochondrial genes encoding proteins related to cellular respiration. Here, we compared the sequences of 13 protein-coding genes in the mitochondrial genome of dwarf blue sheep with those of blue sheep to understand the genetic basis of morphological variation. Using neighbor-joining, maximum-likelihood and Bayesian approaches, we estimated rates of synonymous (d(S)) and nonsynonymous (d(N)) substitutions. Independent analyses showed that no ω ratio was larger than 1, suggesting that all mitochondrial 13 genes were under the purifying selection. Surprisingly, we found that the ω ratio (d(N)/d(S)) of the ATP synthase complex (ATP6 and ATP8) in blue sheep is sixteen times that of dwarf blue sheep (0.340 compared to 0.021). This result was confirmed by a separate analysis of ATP synthase genes from two additional P. schaeferi individuals and two P. nayaur individuals. We hypothesize that the large body size and diverse feeding styles are factors influencing the nonsynonymous substitutions in the ATP synthase complex of blue sheep.

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    ABSTRACT: Abstract The population of blue sheep, Pseudois nayaur, from Helan Mountain in China is considered as a new subspecies. We first determined and annotated its complete mitochondrial genome. The mitogenome is 16,795 bp in length, consisting of 13 protein-coding genes, 22 transfer RNA (tRNA) genes, 2 ribosomal RNA (rRNA) genes and a control region. As in other mammals, most mitochondrial genes are encoded on the heavy strand, except for ND6 and eight tRNA genes, which are encoded on the light strand. Its overall base composition is A: 33.2%, T: 26.6%, C: 26.8% and G: 13.3%. The complete mitogenome of the new subspecies of P. nayaur could provide an important data to further explore the taxonomic status of the subspecies.
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