Tuesday, October 9, 2012

The deadliest sea snake

 ...is actually two species.

Enhydrina schistosa

Enhydrina schistosa, commonly known as the beaked sea snake, is a highly venomous species of sea snake common throughout the tropical Indo-Pacific.The venom of this species is made up of highly potent neurotoxins and myotoxins. The species is considered responsible for the vast majority of deaths from sea snake bites (up to 90% of all sea snake bites). It primarily inhabits coastal and inshore areas and can be abundant in estuaries and lagoons, where it poses a significant risk to fishermen handling nets. And now the surprise as this ‘species’ actually consists of two distinct lineages in Asia and Australia that are not even closest relatives. A group of researchers from Australia, Indonesia, and Sri Lanka were able to show convergence in the characteristic ‘beaked’ morphology of these species which is probably associated with the wide gape required to accommodate their spiny prey. Consequently they elevated the Australian “E. schistosa” to species status and provisionally referred to E. zweifeli. ("Zweifel" is the German word for doubt).

It would have been great if the authors had decided to include COI in their analysis as well (instead of cyt b for example). Their finds will have important implications for snake bite management as the only sea snake anti-venom available is raised against Malaysian E. schistosa. The inclusion of a DNA Barcode would have shown if it too can discriminate between the two species and would have made it a much better alternative to a multi-locus approach which is impracticable in every day use . In fact their mtDNA tree already shows that the Asian and Australian lineages have independent origins. This study will eventually lead to a description and a revision within the genus. DNA Barcodes of the types would be ideal and a great contribution to the DNA Barcode library. 

Given that snake venom has a strong phylogenetic component it is surprising that current treatment of snake bites seems to be unaffected by this. According to the authors the only thing "that has prevented this misidentification from having catastrophic medical implications, is that all sea snake venoms are very streamlined due to feeding on a single higher taxon (bony fish). Consequently all sea snake venoms tested to-date have been well-neutralised by the only available antivenom."

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