This requires a long distance defence from their serpentine enemies, like spitting. The timing of the evolution of venom spitting coincides with key dates in the evolution of early human ancestors. The emergence of spitting in African cobras occurred at around the same time as the separation of hominins from the chimpanzees and bonobos lineage, approximately 7 million years ago. The evolution of spitting in Asian cobras occurred alongside the arrival of Homo erectus in Asia around 2.
Read more: Why do snakes produce venom? Not for self-defence, study shows. In addition, fossils of spitting cobra fangs have been found in ancient hominin sites such as the cradle of humanity in Africa. Current evidence is circumstantial, which means we require more proof. However, venom spitting as a response to trampling by herd animals or being preyed on by birds or mammals is far less supported.
Additional fossils might support or refute our hypothesis. In particular, finding the fossilised remains of spitting cobras that predate the divergence between hominins and chimpanzees would refute our hypothesis.
Rather than being a lineage apart, our human ancestors might have had a direct impact on how these animals evolved. However, using venom that slowly destroys cells in order to cause pain may help a cobra for purposes of predation. In those instances, inflicting direct — and thus rapid — pain is paramount. So, the authors investigated the nociceptive activity of cobra venoms.
For this purpose, they applied venom to mammalian trigeminal neurons. These are sensory neurons derived from trigeminal ganglia that innervate the face and eyes. Using calcium imaging to monitor the activity of the trigeminal neurons, the team saw that all the cobra venoms could activate sensory neurons.
The researchers say this is probably because all the venoms disrupt the cell membrane thanks to the cytotoxic activity of the CTXs.
But the spitting cobra venoms activated the neurons more strongly than the non-spitting cobra venoms did — exactly what such creatures would need to more effectively inflict pain. What was in the spitting cobra venom that accounted for this? Fractionating the venom from three representative spitting cobras into its components, the team found that only those fractions containing CTXs could activate sensory neurons; fractions containing only neurotoxins or PLA 2 s were unable to do so. But then a new wrinkle to the story emerged.
The hypothesis turned out to be correct. Consistent with that finding, use of a PLA 2 inhibitor decreased the ability of the CTX fractions to activate the neurons. Spitting cobra venom indeed had more PLA 2 , compared to the venom of non-spitting cobras. Also, proteomics results showed that there was major variation in PLA 2 between spitting and nonspitting cobra lineages, especially when looking at the African species of spitting cobras.
Phylogenetic analysis showed that there was a duplication of the PLA 2 gene at the time when venom spitting emerged in the ancestor of African spitting cobras. Finally, additional experiments in a mouse model of venom lethality would show no greater lethality of spitting cobra venom vs. This suggested that it was the composition of spitting cobra venom that really made the difference, and that the evolutionary purpose of the enhanced pain by the spitting cobra venom was defense against potential enemies, rather than an offensive maneuver against prey species.
So why did cobra venoms evolve in this way — under what threats could these snakes find themselves that would make venom spitting an effective solution?
The Egyptian cobra's venom is extremely toxic. Its bite can cause a quick death, and it is considered by many to be the serpent used by Cleopatra to commit suicide. Cobra home. These mighty snakes live in Africa and Asia, preferring savannas, open woodlands, plains, and rocky hillsides. Eating out. At dawn and dusk, hungry cobras begin to move and look for a good spot to hunt for their meal. They can go for days or even months without eating, depending on how large their last meal was. The snake's slow metabolism makes this possible.
A mouse, rat, ground squirrel, or rabbit are its main prey items, but cobras may also eat amphibians, birds, lizards, other snakes, and eggs. Cobras use their forked tongue to smell prey. The tongue moves in and out, picking up odor particles from the ground and passing them over a special smelling organ in the roof of the mouth, called the Jacobson's organ.
This helps the snake sniff out its next meal. The cobra, like other venomous snakes, is lightning fast when it strikes. But it has somewhat smaller fangs, so it may strike and chew rather than strike and release, or it may strike several times until the venom has done its job. Hooded hatchlings. A cobra female produces a clutch of eggs each year and usually stays nearby to guard her eggs until they hatch.
A baby cobra, like all snakes, is called a hatchling. It is able to take care of itself from the start and can spread its hood and strike on the same day it hatches. A large yolk sac remains in the hatchling's stomach to give it nourishment for up to two weeks before it needs to find food on its own. The king cobra may grow to be It is found throughout India, southern China, and Southeast Asia.
An international team including IMB's Professor Irina Vetter and Dr Sam Robinson , made the discovery by studying the composition of spitting cobra venoms from three groups of snakes — Asian spitting cobras, African spitting cobras and Rinkhals.
Professor Vetter said the snakes had independently evolved the ability to spit their venoms at enemies. The three different groups of venom-spitting snakes had increased production of an enzyme toxin, phospholipase-A2, which works cooperatively with other venom toxins to maximise pain.
Lead author Professor Nick Casewell from the Liverpool School of Tropical Medicine said venom spitting was ideally suited to deterring attacks from humans.
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