Fossil evidence suggests that cetaceans evolved from artiodactylans. Thus, there was a major dietary change from herbivorous to carnivorous during their transition from a terrestrial to an aquatic environment. However, the molecular evolutionary mechanisms underlying this dietary switch have not been well investigated. Evidence of positive selection of digestive proteinases and lipases of cetaceans was detected: (1) For the four pancreatic proteinase families (carboxypeptidase, trypsin, chymotrypsin, and elastase) examined in this study, each family included only a single intact gene (e.g., CPA1, PRSS1, CTRC, and CELA3B) that had no ORF-disrupted or premature stop codons, whereas other members of each family had become pseudogenized. Further selective pressure analysis showed that three genes (PRSS1, CTRC, and CELA3B) were subjected to significant positive selection in cetaceans. (2) For digestive proteinases from the stomach, PGA was identified to be under positive selection. (3) Intense positive selection was also detected for the lipase gene PLRP2 in cetaceans. In addition, parallel /convergent amino acid substitutions between cetaceans and carnivores, two groups of mammals that have evolved similar feeding habits, were identified in 10 of the 12 functional genes. Although pseudogenization resulted in each family of pancreatic proteinases only retaining one intact gene copy in cetacean genomes, positive selection might have driven pancreatic proteinases, stomach proteinases, and lipases to adaptively evolve a stronger ability to digest a relatively higher proportion of proteins and lipids from animal foods. This study can provide some novel insights into the molecular mechanism of cetacean dietary changes during their transition from land to sea.

化石证据表明鲸目动物是从偶蹄动物进化而来的。因此，在它们从陆地环境到水生环境的过渡过程中，饮食发生了从草食性到肉食性的重大变化。然而，这种饮食转变背后的分子进化机制尚未得到很好的研究。检测到鲸类消化蛋白酶和脂肪酶阳性选择的证据：（1）对于本研究中检测的四个胰腺蛋白酶家族（羧肽酶、胰蛋白酶、糜蛋白酶和弹性蛋白酶），每个家族仅包含一个完整的基因（例如CPA1，PRSS1，CTRC和CELA3B) 没有 ORF 破坏或过早的终止密码子，而每个家族的其他成员已成为假基因。进一步选择压力分析表明，三个基因（PRSS1，CTRC和CELA3B）进行在鲸类显著正选择。(2)对于来自胃的消化蛋白酶，PGA被鉴定为正选择。(3) 脂肪酶基因PLRP2也检测到强阳性选择在鲸类中。此外，在 12 个功能基因中的 10 个中鉴定了鲸目动物和食肉动物（进化出相似饮食习惯的两组哺乳动物）之间的平行/趋同氨基酸置换。虽然假基因化导致每个胰腺蛋白酶家族只在鲸类基因组中保留一个完整的基因拷贝，但正选择可能驱动胰腺蛋白酶、胃蛋白酶和脂肪酶适应性进化出更强的能力，以消化相对较高比例的动物蛋白质和脂质。食物。这项研究可以为鲸类从陆地到海洋过渡期间饮食变化的分子机制提供一些新的见解。