Understanding how organisms adapt to extreme environments is fundamental and can provide insightful case studies for both evolutionary biology and climate-change biology. Here, we take advantage of the vast diversity of lifestyles in ants to identify genomic signatures of adaptation to extreme habitats such as high altitude. We hypothesized two parallel patterns would occur in a genome adapting to an extreme habitat: 1) strong positive selection on genes related to adaptation and 2) a relaxation of previous purifying selection. We tested this hypothesis by sequencing the high-elevation specialist Tetramorium alpestre and four other phylogenetically related species. In support of our hypothesis, we recorded a strong shift of selective forces in T. alpestre, in particular a stronger magnitude of diversifying and relaxed selection when compared with all other ants. We further disentangled candidate molecular adaptations in both gene expression and protein-coding sequence that were identified by our genome-wide analyses. In particular, we demonstrate that T. alpestre has 1) a higher level of expression for stv and other heat-shock proteins in chill-shock tests and 2) enzymatic enhancement of Hex-T1, a rate-limiting regulatory enzyme that controls the entry of glucose into the glycolytic pathway. Together, our analyses highlight the adaptive molecular changes that support colonization of high-altitude environments.

中文翻译：

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亚高山蚂蚁的选择转变的基因组特征及其生理适应性。

了解生物如何适应极端环境是基础，并且可以为进化生物学和气候变化生物学提供有见地的案例研究。在这里，我们利用蚂蚁的多种生活方式来确定适应极端栖息地（例如高海拔地区）的基因组特征。我们假设在适应极端栖息地的基因组中会出现两种平行模式：1）对与适应相关的基因进行强阳性选择，以及2）先前纯化选择的放宽。我们通过对高海拔专家Tetramorium alpestre和其他四个系统发育相关物种进行测序来检验该假设。为了支持我们的假设，我们在T. alpestre中记录了选择性力的强烈变化，尤其是与所有其他蚂蚁相比，多样化和放松选择的强度更高。我们进一步弄清了候选基因在基因表达和蛋白质编码序列中的分子适应性，这些适应性已通过我们的全基因组分析确定。特别是，我们证明T. alpestre具有1）在冷激试验中stv和其他热休克蛋白的表达水平更高，以及2）Hex-T1的酶促增强，Hex-T1是一种控制进入的限速调节酶葡萄糖进入糖酵解途径。总之，我们的分析突出了支持高海拔环境殖民化的适应性分子变化。