PHYLOGENETIC RELATIONSHIPS OF 20 SNAKE SPECIES BASED ON PARTIAL SEQUENCES OF 12S rRNA GENE

摘要

The conservative morphological characters of snakes complicate the analysis of phylogenetic relationships among these organisms. Recently, some authors have employed DNA sequence analysis to examine phylogenetic relationships among snakes but little work on Chinas snakes has been published to date. The evolutionary history of snakes still remains controversial. In the current investigation, we try to shed light on these relationships via DNA sequence analysis of the mitochondrial 12S rRNA gene in 20 species of snake representing 13 genera from 4 families. About 800 bp of gene fragments from these species were sequenced, of which 494 variable sites were identified after combining and aligning the data with the homologous sequence of Sphenodon punctatus. A phylogenetic tree constructed using the neighbor joining method with Sphenodon punctatus as the outgroup indicates that the snakes examined in this study are clustered in four major clades corresponding to their four families. The first clade includes the 2 Boidae species, Erys tataricus and Python molurus biritattatus, the second is comprised of the 3 Viperidae species, Deinagkistrodon acutus, Trimeresurus stejneger and Vipera ursinii, the third contains the two Elapidae species, Naja naja and Bungarus multicinctus, and finally, the remaining 13 species of Colubridae form a large lineage in the phylogenetic tree. Consistent with the widely accepted opinion that it is the most primitive family among all current snakes, the Biodae branch diverges from the base of the tree. The Colubridae and Elapidae cluster together with a bootstrap value of 93 before they combine with the Viperidae lineage, strongly supporting the assumption that the Elapidae share an ancient ancestor with the Colubridae, rather than the Viperidae. Within the 13 species of the Colubridae, there are two major clades, the Rhabdophis and Sinonatrix clade, and the Zaocys, Ptyas, Dinodon and Elaphe clade, with bootstrap values of 99 and 98 respectively. In the second clade, seven species of Elaphe form a common branch before they cluster with other genera, contrary to Dessauers assumption of the polyphyletic origin of this genus.