Cetacean Osmotic Adjustment And Epidermal Derivatives And Other Related Genes In The Molecular Evolution

The ancestor of cetaceans returned from the land to the sea approximately50million years ago, and finally they became fully aquatic mammals34million years ago. During the change of life environment, ancestors of cetacean needed to face tremendous pressure and they experienced dramatic changes of physiological and morphological. The maintenance of homeostasis via regulation of water and electrolyte levels was one of the most critical challenges they encountered. Osmoregulation is to maintain the balance of body fluid through water conservation and salt excretion in cetaceans. The physiological change of rencular structure have suggested that may have facilitated cetaceans adaptation to hyperosmotic environment, however, the molecular basis of these mechanisms remains poorly explored. In this study, we chose the candidate genes related to osmoregulation to detect the selective pressures.There are five kinds of genes related to osmoregulation:salt regulated gene (Na+-K+-ATPase), water regulated genes (Aquaporin1-4), Angiotensin Converting Enzyme (ACE), Angiotensinogen (AGT) and Renin (REN) in Renin-angiotensin-aldosterone system (RAAS), urea transport genes (UTA and UTB), and the hormonal regulated genes (AVP and ANP). We compared the genes involved in osmoregulation in cetaceans with their counterparts in terrestrial mammals to test whether adaptive evolution occurred during secondary aquatic adaptation. It was demonstrated positive selection acting on ACE, AGT, UTA, and AQP2. The positive selection of AQP2and UTA is helpful to enhance the capacity for water and urea transport, thereby leading to the concentration of urine, which is an efficient mechanism for maintaining the water balance in cetaceans. By contrast, a series of positively selected amino acid residues identified in the ACE and AGT (two key members of RAAS) of cetaceans suggests that RAAS might have been adapted to maintain the water and salt balance in response to a hyperosmotic environment. Radical amino acid changes in the positively selected sites were distributed among most internal and terminal branches of the cetacean phylogeny, which suggested the pervasively adaptive evolution of osmoregulation during the origin and subsequent diversification. The present study represented the first comprehensive analysis of molecular evolution of osmoregulation-related genes in cetaceans in response to selection pressure from a generally hyperosmotic environment suggesting that cetaceans may have evolved an effective and complex mechanism for osmoregulation.Besides renal system, the skin also plays key roles in homeostasi. The research of the skin structure in cetaceans revealed that The epidermis derivatives, including the hair, hair follicles, sebaceous glands and sweat gland, are absent. The change of cetaceans’ skin structure is helpful to reduce the loss of water and to avoid the cell to contact with the hypertonic environment. However, molecular mechanism about the loss of epidermal derivatives in cetaceans is still unclear. The EDA pathway is related to the development of epidermal derivatives such as hair follicle, sweat glands, and sebaceous glands. For this reseason, we tried to investigate the key genes in the EDA pathway to reveal the adaptive evolution of epidermal derivatives.According to the test of selection pressure on the three key genes (i.e., EDA, EDAR, EDARADD) in EDA pathway, these genes in cetaceans underwent adaptive evolution. EDA and EDAR gene had higher rate of non-synonymous mutation accumulation in cetaceans compared with terrestrial mammals suggesting the positive selection may act on cetaceans. The ω values in EDAR and EDARADD gene are not significantly different with one on ancestor of baleen whales. Further in EDAR gene, there are5amino acids missing in baleen whales. This result showed that EDAR and EDARADD genes undergo relaxation of selective pressure in cetaceans. In addition, some specific amino acids, most of which are radical changes, have been found in cetaceans. The properties of amid acid change may influence the protein space structure, and change the function of genes. In conclusion, the EDA pathway genes in cetaceans underwent adaptive evolution which led to the absent of epidermal derivatives such as hair follicle, sweat glands, and sebaceous glands. It is also the adaptive evolution of cetaceans to adapt the aquatic environment.Insects are unique among invertebrates for their ability to fly, which raises intriguing questions about how energy metabolism in insects evolved and changed along with flight. Although physiological studies indicated that energy consumption differs between flying and non-flying insects, the evolution of molecular energy metabolism mechanisms in insects remains largely unexplored.Considering that about95%of adenosine triphosphate (ATP) is supplied by mitochondria via oxidative phosphorylation, we examined13mitochondrial protein-encoding genes to test whether adaptive evolution of energy metabolism-related genes occurred in insects. The analyses demonstrated that mitochondrial DNA protein-encoding genes are subject to positive selection from the last common ancestor of Pterygota, which evolved primitive flight ability. Positive selection was also found in insects with flight ability, whereas no significant sign of selection was found in flightless insects where the wings had degenerated. In addition, significant positive selection was also identified in the last common ancestor of Neoptera, which changed its flight mode from direct to indirect. Interestingly, detection of more positively selected genes in indirect flight rather than direct flight insects suggested a stronger selective pressure in insects having higher energy consumption. In conclusion, mitochondrial protein-encoding genes involved in energy metabolism were targets of adaptive evolution in response to increased energy demands that arose during the evolution of flight ability in insects...