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. 2012 Sep;12(5):500-5. doi: 10.1016/j.mito.2012.07.107. Epub 2012 Jul 20.
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.
假猫属包括两个变化的分类群，蓝羊（Pseudois nayaur）和小蓝羊（Pseudois schaeferi），它们在形态和生态位上表现出显著的地理变异，表明这两种山羊之间可能存在显著的适应性分化。蓝羊广泛分布于青藏高原及其周边山脉，从中亚一直延伸到西藏；而小蓝羊仅分布于四川省巴塘县附近的长江上游（金沙江）峡谷及其相邻山脉。尽管它们都适应高海拔环境，但濒危的小蓝羊与蓝羊相比表现出独特的形态变异和生态位转移。线粒体在氧气利用和能量代谢中起着重要作用。这些高海拔物种的高能耗生活方式可能改变了与细胞呼吸相关的线粒体基因编码蛋白的选择机制。在这里，我们比较了小蓝羊和蓝羊线粒体基因组中 13 个蛋白编码基因的序列，以了解形态变异的遗传基础。使用邻接法、最大似然法和贝叶斯法估计了同义（d(S))和非同义（d(N))取代率。独立分析表明，没有一个ω值大于 1，这表明所有线粒体 13 个基因都受到纯化选择。令人惊讶的是，我们发现蓝羊中 ATP 合酶复合物（ATP6 和 ATP8）的 ω值（d(N)/d(S))是小蓝羊的 16 倍（0.340 对 0.021）。这一结果通过对另外两个小蓝羊个体和两个蓝羊个体的 ATP 合酶基因的单独分析得到了证实。我们假设大的体型和多样化的摄食方式是影响蓝羊 ATP 合酶复合物非同义替换的因素。
