The Evolution Of WDR62, CDK5RAP2 And CEP152 And Its Relationship With The Increase In Brain Capacity Of Cetaceans

The brain size expansion is a remarkable feature in cetacean evolution, and there are some evidences from anatomy and computed tomography that the first enlargement of brain size, also expanded the most obvious was in the early origin of suborder Odontoceti and the seconds was during the evolution of family Delphinoids. Based on the study of ecological and physiological, researchers have put forward three hypotheses in order to explain the brain expansion. The first hypothesis presented that the enlargement of cetacean brain is a direct product of adaptation to a fully aquatic lifestyle. The second's is proposed by Manger pointed out that the brain size increased is to generated more thermogenic glial cells to counteract heat loss during a decrease in ocean temperatures, but this hypothesis was suspected soon. The last also is the more generally accepted view hypothesed that the enlarged brain size of cetaceans was primarily a response to social forces and cognitive demands. However, the genetic mechanism of the brain size expansion is still unclear. In this article, we selected WDR62, CDK5RAP2 and CEP 152, three of the seven MCPH genes which are the key genes that control the brain size to study:1) whether the evolution of the MCPH genes corresponded with the two brain size expansion events, 2) whether cetacean and primate have suffered the similar selection pressure,3) whether the evolution of the MCPH genes are association with the brain phenotypes of cetaceansHere, we investigated 3 MCPH gene in 14 representative cetacean species and compared the homologous sequences with other mammals. We found that WDR62, CDK5RAP2 and CEP 152 are all detected significantly positive selection in cetaceans especially in the lineages leading to the suborder Odontoceti and the superfamily Delphinoids, which coincides with the two brain size expansion events during cetacean evolution. And we did not detect positive selection in the common ancestor of cetaceans suggested that the cetacean brain size increased is not the adaption to the aquatic lifestyle but a response to the social forces and cognitive demands. In addition, the positive selection of the three genes restricted in cetaceans and primates, two distantly related taxa but both have a larger brain size, and the most striking is that we detected eight convergence evolution sites between primates and cetacean, suggested that brain size expansion is the result of the convergent evolution in cetaceans and primates. Therefore, the evolution of the MCPH genes played an important role in brain size expansion.