BACKGROUND The transition from land to sea by the ancestor of cetaceans approximately 50 million years ago was an incredible evolutionary event that led to a series of morphological, physiological, and behavioral adaptations. During this transition, bone microstructure evolved from the typical terrestrial form to the specialized structure found in modern cetaceans. While the bone microstructure of mammals has been documented before, investigations of its genetic basis lag behind. The increasing number of cetaceans with whole-genome sequences available may shed light on the mechanism underlying bone microstructure evolution as a result of land to water transitions. RESULTS Cetacean bone microstructure is consistent with their diverse ecological behaviors. Molecular evolution was assessed by correlating bone microstructure and gene substitution rates in terrestrial and aquatic species, and by detecting genes under positive selection along ancestral branches of cetaceans. We found that: 1) Genes involved in osteoclast function are under accelerated evolution in cetaceans, suggestive of important roles in bone remodeling during the adaptation to an aquatic environment; 2) Genes in the Wnt pathway critical for bone development and homeostasis show evidence of divergent evolution in cetaceans; 3) Several genes encoding bone collagens are under selective pressure in cetaceans. CONCLUSIONS Our results suggest that evolutionary pressures have shaped the bone microstructure of cetaceans, to facilitate life in diverse aquatic environments.

中文翻译：

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加速进化和多样化选择推动了鲸类骨骼微结构的适应。


背景技术大约5000万年前，鲸目动物的祖先从陆地到海洋的转变是一个令人难以置信的进化事件，导致了一系列形态、生理和行为的适应。在这个转变过程中，骨骼微观结构从典型的陆地形式演化为现代鲸类动物的特殊结构。虽然哺乳动物的骨骼微观结构以前已有记录，但对其遗传基础的研究却滞后。拥有全基因组序列的鲸目动物数量不断增加，可能有助于揭示陆地到水的转变导致骨微结构进化的机制。结果鲸类骨骼微结构与其多样化的生态行为一致。通过关联陆地和水生物种的骨骼微结构和基因替代率，并通过检测鲸目动物祖先分支正选择下的基因来评估分子进化。我们发现：1）涉及破骨细胞功能的基因在鲸目动物中加速进化，这表明在适应水生环境过程中骨重塑中发挥着重要作用； 2）Wnt通路中对骨骼发育和体内平衡至关重要的基因显示出鲸类动物进化趋异的证据； 3）在鲸类动物中，编码骨胶原的几个基因受到选择性压力。结论我们的结果表明，进化压力塑造了鲸目动物的骨骼微观结构，以促进不同水生环境中的生命。