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

Abstract

Aim The biogeography of Southeast Asia has been greatly affected by Pleistocene sea‐level changes and the consequent alteration of coastline and land mass configurations. We investigated the effect of these Pleistocene events on genetic divergence in Cerberus rynchops, the Bockdam, an Asian water snake (Homalopsinae) associated with tidal mudflats and coastal mangrove forests in Southeast Asia. Location Localities for the Cerberus included the Andaman sea coast of Thailand, Sumatra, and Borneo (Sunda Shelf localities), the Philippines and Sulawesi, and from northern Australia (Sahul Shelf). Methods We analysed mtDNA sequences (12 s, 16 s, and cyt b) from seven C. rynchops populations (twenty‐six specimens), from two specimens of Cerberus microlepis (a freshwater species known only from Lake Buhi in the Philippines), and from one Enhydris enhyris (Schneider), another homalopsine used as an outgroup. Results We found a strong correlation between genetic divergence and geographical 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 genetically similar (mean divergence = 2.1%, range = 0.7–2.8%) compared to the C. rynchops population from northern Australia (mean divergence from all other Cerberus populations = 6.6%, range = 6.0–7.3%). This divergence was comparable to that observed between the E. enhydris outgroup and all Cerberus populations (mean distance = 7.3%, range = 6.8–8.6%). Main conclusions These findings suggest a relatively high degree of movement 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 ecology. We discuss how the dispersal of the coastal, saltwater tolerant C. rynchops would have been affected by changing configurations of Pleistocene coastlines and the implications of these results for the systematics of Cerberus.

Conservation status of the White-Bellied Sea-Eagle Haliaeetus leucogaster in Australia determined using mtDNA control region sequence data

“…160,000 years BP, during the late Pleistocene, sea-levels were at their lowest, approximately 150 m below current levels, which effectively joined the islands of the Sunda shelf to the Asian mainland and exposed the Sahul shelf (Chappell 1983;Hewitt 2000;Karns et al 2000). Although deep-water barriers separated the two shelves (Karns et al 2000), distances between islands were relatively small and unlikely to pose a significant barrier to the movement of birds or the rapid expansion of H. leucogaster through Malaysia to Australia (Keast 1981a;McManus 1985;Karns et al 2000). The timing of low sea-levels is remarkably consistent with the genetically based estimate of 160,000 years since expansion into Australia.…”

“…Both Timor and New Guinea are known to have functioned as an entry route to Australia (Keast 1981a;McManus 1985;Ericson et al 2002). Until only 8000 years BP, exposure of the Sahul shelf reduced the distance between Timor and Australia to less than 100 kilometers (Keast 1981a;Karns et al 2000). The retention of a Clade 1-1 haplotype in Western Australia is suggestive of colonisation via this route.…”

Phylogeny and biogeography of Philippine bent-toed geckos (Gekkonidae: Cyrtodactylus) contradict a prevailing model of Pleistocene diversification

“…In addition to the geological processes that created the island arc system, Pleistocene sea-level fluctuations have caused repeated and dramatic changes in the size and connectivity of islands (Heaney, 1986;Hall, 1996Hall, , 1998Hall, , 2001Rohling et al, 1998;Karns et al, 2000;Siddall et al, 2003). During periods of lower sea levels (100-140 m below current levels), nearby islands became connected into island platforms known as Pleistocene Aggregate Island Complexes (PAICs: Diesmos, 2002, 2009).…”

The biogeographical relations of the frogs and snakes of Sundaland

“…Four are distributed in coastal areas from India to Java and Borneo, and these plus two that are known from Burma and Indo‐China to Borneo and Java probably have been able to disperse through Sundaland during much of the Pleistocene when sea level was at least 30 m BPL, or about 50% of the last 250,000 years (Voris, 2000). One homalopsine species, Cerberus rynchops (Schneider), is particularly abundant in mangrove swamps and tidal mud flats, and probably spread as fast as mud flats and associated vegetation developed in new areas (Karns et al. , 2000).…”