The intertidal zone is one of the most stressful environments, with extreme shifts in temperature, salinity, pH and oxygen concentration. Marine molluscs, particularly chitons that belong to the category of ecologically significant organisms, survive in this extreme environment, and are ideal systems for studying stress adaptation. Mitochondria are known to be critical for energy homeostasis, and changes in environmental factors result in their dysfunction and consequent injury to the organism. Intertidal organisms are exception in this respect because they are capable of maintaining mitochondrial integrity. Here, we used mitochondrial genetic components from seven chitons of the intertidal zone to infer phylogenetic relationships. Selection analyses on individual protein-coding genes (PCGs) were performed to identify and map potentially adaptive residues in the modelled structures of the mitochondrial respiratory chain complexes. The results showed significant amino acid changes in sites under diversifying selection for all the PCGs, indicating that the mitochondrial genome in chitons is undergoing adaptive evolution. Such sites were observed in the proton pump as well as in the translocation channel of the transmembrane helices and the surrounding loop regions, thus implying functional modification of the mitochondrial proteins essential for survival in the dynamic environment of the intertidal zone.

中文翻译：

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深入了解潮间带石鳖线粒体基因组的适应性进化

潮间带是压力最大的环境之一，温度、盐度、pH 值和氧气浓度变化很大。海洋软体动物，特别是属于生态重要生物类别的石鳖，在这种极端环境中生存，是研究压力适应的理想系统。众所周知，线粒体对能量稳态至关重要，环境因素的变化会导致它们的功能障碍，进而对生物体造成伤害。潮间带生物在这方面是个例外，因为它们能够维持线粒体的完整性。在这里，我们使用来自潮间带七个石鳖的线粒体遗传成分来推断系统发育关系。对单个蛋白质编码基因 (PCG) 进行选择分析，以识别和绘制线粒体呼吸链复合物模型结构中潜在的适应性残基。结果表明，在所有PCGs的多样化选择下，​​位点的氨基酸发生了显着变化，表明石鳖中的线粒体基因组正在经历适应性进化。在质子泵以及跨膜螺旋和周围环区域的易位通道中观察到这些位点，因此暗示线粒体蛋白的功能修饰对于在潮间带的动态环境中生存至关重要。结果表明，在所有PCGs的多样化选择下，​​位点的氨基酸发生了显着变化，表明石鳖中的线粒体基因组正在经历适应性进化。在质子泵以及跨膜螺旋和周围环区域的易位通道中观察到这些位点，因此暗示线粒体蛋白的功能修饰对于在潮间带的动态环境中生存至关重要。结果表明，在所有PCGs的多样化选择下，​​位点的氨基酸发生了显着变化，表明石鳖中的线粒体基因组正在经历适应性进化。在质子泵以及跨膜螺旋和周围环区域的易位通道中观察到这些位点，因此暗示线粒体蛋白的功能修饰对于在潮间带的动态环境中生存至关重要。