Snake venom did not evolve as self-defense, according to a paper published in the journal Toxins.
The study by Ward-Smith et al doesn’t support the hypothesis that natural selection for antipredator defense played an important role in the origin of snake venom or front-fanged delivery systems in general, although there may be intriguing exceptions to this rule. Image credit: J.E. Nate / CC BY-SA 3.0.
To provide efficient defense from a predator, the snake venom would need to provide sufficient instant pain to deter the predator and enable the snake to escape, much as a bee-sting hurts immediately.
Surprisingly, few venomous snake bites cause immediate pain, implying that the venom make-up has not evolved for a defensive primary purpose.
“We know that snake venom is used primarily for foraging, for overpowering and killing prey,” said Dr. Wolfgang Wüster, a world-renowned expert on snake venom evolution at Bangor University.
“However, we also know that snakes use their venom in self-defense — that’s why so many people get bitten, and sometimes killed, by venomous snakes worldwide.”
“We wanted to investigate whether defense was a driver in venom evolution.”
Dr. Wüster, Bangor University student Harry Ward-Smith and their colleagues used an online survey of snakebite victims to test a key prediction of a defensive function, that envenoming should result in the rapid onset of severe pain.
From the analysis of 584 snakebite reports, involving 192 species of venomous snake, they found that the vast majority of bites do not result in severe early pain.
“Our results suggest little evidence for widespread evolution of venoms driven by their use in defense, though interesting exceptions likely exist such as the defensive use of venom ‘spitting’ in some cobras, and these specific cases deserve further study,” said co-author Dr. Kevin Arbuckle, from Swansea University.
“Even though we might have expected defending your life to be more important than feeding, it turns out that natural selection for diet does seem to be the main driver of venom evolution in snakes,” Dr. Wüster added.
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Harry Ward-Smith et al. 2020. Fangs for the Memories? A Survey of Pain in Snakebite Patients Does Not Support a Strong Role for Defense in the Evolution of Snake Venom Composition. Toxins 12 (3): 201; doi: 10.3390/toxins12030201
