'Obesity' is healthy for cetaceans? Evidence from pervasive positive selection in genes related to triacylglycerol metabolism.

Cetaceans are a group of secondarily adapted marine mammals with an enigmatic history of transition from terrestrial to fully aquatic habitat and subsequent adaptive radiation in waters around the world. Numerous physiological and morphological cetacean characteristics have been acquired in response to this drastic habitat transition; for example, the thickened blubber is one of the most striking changes that increases their buoyancy, supports locomotion, and provides thermal insulation. However, the genetic basis underlying the blubber thickening in cetaceans remains poorly explored. Here, 88 candidate genes associated with triacylglycerol metabolism were investigated in representative cetaceans and other mammals to test whether the thickened blubber matched adaptive evolution of triacylglycerol metabolism-related genes. Positive selection was detected in 41 of the 88 candidate genes, and functional characterization of these genes indicated that these are involved mainly in triacylglycerol synthesis and lipolysis processes. In addition, some essential regulatory genes underwent significant positive selection in cetacean-specific lineages, whereas no selection signal was detected in the counterpart terrestrial mammals. The extensive occurrence of positive selection in triacylglycerol metabolism-related genes is suggestive of their essential role in secondary adaptation to an aquatic life, and further implying that ‘obesity’ might be an indicator of good health for cetaceans.

鲸目动物是一类次生适应海洋的哺乳动物，它们从陆地过渡到完全水生的栖息地的历史充满神秘，随后在世界各地的水域中发生了适应性辐射。为了适应这种剧烈的栖息地转变，鲸目动物获得了许多生理和形态特征；例如，增厚的鲸脂是最显著的变化之一，它增加了鲸目动物的浮力，辅助运动，并提供隔热作用。然而，鲸目动物鲸脂增厚的遗传基础仍未得到充分探究。在此，对具有代表性的鲸目动物和其他哺乳动物中与三酰甘油代谢相关的88个候选基因进行了研究，以检验增厚的鲸脂是否与三酰甘油代谢相关基因的适应性进化相匹配。在88个候选基因中的41个检测到了正选择，对这些基因的功能特性分析表明，它们主要参与三酰甘油的合成和脂解过程。此外，一些关键的调控基因在鲸目动物特有的谱系中经历了显著的正选择，而在相应的陆地哺乳动物中未检测到选择信号。三酰甘油代谢相关基因中广泛出现的正选择表明它们在对水生生活的次生适应中起着至关重要的作用，并进一步暗示“肥胖”可能是鲸目动物健康的一个指标。