Phylogeography of the Russell's viper (Daboia russelii) complex in relation to variation in the colour pattern and symptoms of envenoming

Abstract

The Russell’s viper complex has a patchy (relict) distribution over large areas of Asia from Pakistan to Taiwan and the Lesser Sunda islands. In many areas it is the primary cause of snakebite mortality, and hence a serious medical problem. A multigene mitochondrial gene tree, supported by multivariate morphometry and basic colour pattern, suggests a primary split in the organismal phylogeny giving distinct, diagnosable, eastern and western forms that we recognize as full species: Daboia russelii (west of the Bay of Bengal) and Daboia siamensis (east of the Bay of Bengal). The clinical symptoms of human envenoming show marked geographic variations that are broadly unrelated to the phylogeny. The molecular phylogeny, together with current distribution and fossil record, suggests cycles of extreme expansion and contraction for this complex. Further studies on venom variation, diet and local population phylogeny are required, but the local and regional variation in symptoms may be the result of fixation of venom genes during cyclical bottlenecks which could explain the haphazard, non-phylogenetic pattern of symptoms of envenomation in this species complex.