Adaptive Evolution Study Of Snake Venom Genes Of Gloydius With Differential Diets

Snake venom functions as a weapon for incapatitating, immobilizing,and digesting their prey,as well as defensing against predators. Sanke venoms present an extraordinarily evolutionary diversity,while the forces that drive the evolutionary diversification of snake venom remain controversial.The traditional predation hypothesis proposes predation as a major force, while the neutral hypothesis proposes that venom diversity largely results from neutral evolutionary processes.In this study,we used seven Asian pitvipers (Gloydius) taxa with different diets as model system to test the evolutionary force underlie the evolution of snake venom genes PLA2,Disintegrin-like, Thrombin-like, respectively.The result showed that,the strong signal of positive selection of PLA2gene was found for Gloydius brevicaudus, and14nucleotide sites of positive selection were detected suggesting an adaptative evolution of the PLA2gene in Gloydius brevicaudus. These positive seletion sites were further found located on the surface of the structure of the PLA2protein,near the catalytic active center suggesting a change of interaction between PLA2proteins and its receptors.For the Disintegrin-like gene, a strong positive selection signal was found Gloydius brevicaudus and G.s.qianshanensis. And8amino acid substitutions were detected in G.s.qianshanensis. One of the8sites is V54,corresponded to the cysteine residues,and the mutation of this site may change the three dimensional structure of this proteins.For the Thrombin-like gene, a strong signal of positive selection was found in Gloydius brevicaudus,and three amino acid substitutions are detected suggesting an adaptive evolution of Thrombin-like gene in Gloydius brevicaudus.The positive selection signal detected in different taxa may suggest an important role of natural selection,possibily diets differentiations,in evolutionary diversification of the three snake venom genes.