Population evolution of the Asiatic cobra (Naja naja) species complex
The Asiatic cobras of the genus Naja constitute a group of medically important venomous snakes. Until now, their taxonomy has been extremely confused. This study uses multivariate analysis of morphological characters recorded from museum material in order to elucidate the population systematics of this complex. The Asiatic cobra complex, hitherto considered to be monospecific, was found to consist of eight separate species: the Central Asian cobra, from the Caspian Sea to India; the Indian spectacled cobra, from India, and neighbouring countries; the monocellate cobra, from north-eastern India, Indochina and northern Malaysia; the Chinese/Indochinese spitting cobra, from south-eastern China and Indochina; the equatorial spitting cobra, from the Malayan Peninsula, Sumatra, Borneo and Palawan; the southern Indonesian spitting cobra, from Java and the Lesser Sunda Islands; the southern Philippine spitting cobra, from the south-eastern Philippines; and the northern Philippine cobra, from the northern Philippines. The pattern of geographic variation within these species is investigated. The species are described, and the differences between them outlined, in order to allow the identification of specimens. The results are related to literature data on cobra bites and venom composition. Considerable immunological variation between the venoms of different cobra taxa has been reported, and this study has shown that in some cases, two species whose bites require different antivenoms occur sympatrically over large areas, emphasising the medical importance of venomous snake systematics. Variation in fang structure is also investigated, and related to literature reports on the incidence of spitting behaviour in these snakes. Two species are incapable of spitting, the other six show a varying degree of adaptation to this defensive behaviour. Finally, the biogeographical factors which may account for the present-day distributions of these species are investigated.