New research by a Swansea University scientist has examined why cobras have evolved to be the only snakes to spit deadly venom and how this is linked to other cobra behaviour, which may help to address the snakebite crisis in parts of Africa and Asia.
Dr Kevin Arbuckle at the College of Science worked with an international team of collaborators and published in the journal ‘Toxins’ a study on cobras, a group of snakes that have evolved multiple times to ‘spit’ a tissue-destroying, or ‘cytotoxic’, venom. This type of venom is unusual amongst the wider group of snakes cobras belong to, which more typically attacks the nervous system to paralyse their prey.
The study found that the way in which cobras warn predators by rising up to face the threat and spreading its hood was important in driving the evolution of cytotoxic venom and the ability to ‘spit’ this into the eyes of predators.
The results of the study suggest that cytotoxicity of a cobra’s venom evolved primarily as a defense mechanism and that this co-evolved twice alongside hooding behavior: once in the ring-necked spitting cobraand ‘true’ cobras and again, independently, in king cobras.
The researchers also found that the evolution of cytotoxic venom combined with hooding displays provided the selection pressure for spitting behavior. Although unique to cobras amongst venomous snakes, they found that spitting evolved independently three times within cobras – in the ring-necked spitting cobra and also in both the African and Asian ‘true’ cobras.
The researchers also suggest that the bold and distinctive hood pattern of cobras such as the famous spectacled cobra of India might act as an additional defensive warning that is associated with painful cytotoxic venom.
Dr Kevin Arbuckle, a lead author on the study, said: “It is known that in the developing world, snakebites affect the poor, and young males in particular are at risk. Suffering a snakebite can result in lifelong disabilities from tissue-destroying venoms and render victims unable to carry out manual work, and this represents a considerable socio-economic burden.
“Our research seeks to understand the evolutionary pressure that shapes the activity of snake venoms and could help to address the snakebite crisis in sub-Saharan Africa and southern Asia by providing insights into snake behaviour and toxicity. For instance, clinicians should not expect tissue damage only from spitters when treating cobra bites, and antivenom developers should also bear this variation in mind.”
Read the research here
King Cobra by Kevin Messenger
Red necked black spitting cobra by Randy Ciuros
- Wednesday 3 May 2017 12.59 BST
- Monday 13 March 2017 16.08 GMT
- Swansea University