Biogeographical implications of mitochondrial DNA variation in the bockadam snake (Cerberus rynchops, Serpentes : Homalopsinae) in Southeast Asia

Aim The biogeography of Southeast Asia has been greatly affected by Pleisto cene sealevel changes and the consequent alteration of coastline and land m ass configurations. We investigated the effect of these Pleistocene events on genetic divergence in Cerberus rynchops, the Bockdam, an Asian water sna ke (Homalopsinae) associated with tidal mudflats and coastal mangrove fores ts in Southeast Asia. Location Localities for the Cerberus included the Andaman sea coast of Thai land, Sumatra, and Borneo (Sunda Shelf localities), the Philippines and Sul awesi, and from northern Australia (Sahul Shelf). Methods We analysed mtDNA sequences (12 s, 16 s, and cyt b) from seven C. r ynchops populations (twenty-six specimens), from two specimens of Cerberus microlepis (a freshwater species known only from Lake Buhi in the Philippin es), and from one Enhydris enhyris (Schneider), another homalopsine used as an outgroup. Results We found a strong correlation between genetic divergence and geogra phical distance (r = 0.922, P < 0.001) and the biogeographic history of the region. Cerberus rynchops populations from the Sunda Shelf localities, the Philippines, Sulawesi and C. microlepis from the Philippines were genetica lly similar (mean divergence = 2.1%, range = 0.7-2.8%) compared to the C. r ynchops population from northern Australia (mean divergence from all other Cerberus populations = 6.6%, range = 6.0-7.3%). This divergence was compara ble to that observed between the E. enhydris outgroup and all Cerberus popu lations (mean distance = 7.3%, range = 6.8-8.6%). Main conclusions These findings suggest a relatively high degree of movemen t and gene flow among Sunda Shelf localities, the Philippines, and Sulawesi (biogeographic region west of Weber's Line) and isolation of the northern Australian (Sunda Shelf) Cerberus. Taxa will be differentially affected by these Pleistocene sea level changes dependent on their physiology and ecolo gy. We discuss how the dispersal of the coastal, saltwater tolerant C. rync hops would have been affected by changing configurations of Pleistocene coa stlines and the implications of these results for the systematics of Cerber us.