The saliva of vampire bats is considered to be a subtype of venom. Common vampire bats (Desmodus rotundus), Hairy-legged vampire bats (Diphylla ecaudata) and White-winged vampire bats (Diaemus youngi) are found from Mexico to southern Argentina. They produce saliva with anticoagulant properties to help them feed on the blood of their prey (Ligabue-Braun, Verli, & Carlini, 2012).
A Common Vampire Bat (Image 1).
The purpose of the vampire bat's venom is to thin the blood of its prey and to anaethetise the area, allowing the bat to feed for extended amounts of time (up to several hours) without being noticed. It has been suggested that rather than the venom causing the painless bite, the young bats how to bite without inflicting pain through trial and error. These bats mostly feed on farm animals - such as cattle, horses, goats, pigs and sheep - but they will also feed on poultry, wild prey and humans. To reduce the risk of the bat being injured, it will normally feed when its prey is asleep. Vampire bats have large, sharp upper incisor teeth that produce a crater-like, sharply circumscribed wound that is approximately 4 mm wide. The bite is inflicted on the bare skin, with the victim's hair being combed or parted by the bat. The saliva enters the body and thins the blood, ensuring that it does not clot. The bat then uses its tongue to lap up the blood. There are two classes of anticoagulants in the vampire bat's saliva. The major class is called plasminogen activators and they produce the localised breakdown of proteins in tissue remodelling, wound healing and neuronal plasticity. This class is made up of many proteins and it is used by the bat to degrade blood clots. Besides the blood thinning effects, the vampire bat venom also causes an immune response on preys frequently fed upon (Ligabue-Braun, Verli, & Carlini, 2012).
A vampire bat feeding (Image 2).
A vampire bat's skull (Image 3).
Vampire bats have modified physiology that enables them to use blood as their only source of food and water. Their gastroesophageal-duodenal junction is T-shaped and their stomach is tubular. This allows the ingested blood to first enter the intestine and then overflow into the stomach. The stomach is used to store blood and absorb water. After the blood is ingested, most of the water is eliminated by instant urine production. The highly nitrogenous blood remains are then processed with very little water, so the bats are able to cope with high levels of urea in their urine (equivalent levels are seen in desert mammals). The bats have a reduced metabolism whilst they digest and they lack storage fat tissue, so they must feed daily to survive (Ligabue-Braun, Verli, & Carlini, 2012).
References
Ligabue-Braun,
R., Verli, H., & Carlini, C. (2012). Venomous mammals: A review. Toxicon
, 59, 680-695.
Images
Brilliant! I really didn’t know that vampire bats had venom! I’m curious – if the saliva prevents coagulation, how long does it take for a wound caused by a vampire bat to stop flowing and start clotting? Why do you think that vampire bats show a relatively restricted distribution (i.e. they don’t seem to occur in Europe, Africa, Asia or Australia)? Great information this week!
ReplyDeleteThe vampire bat saliva allows a wound that would normally clot in 15 minutes (like a simple cut) to flow for up to 3 to 8 hours. The paper mentioned that due to the diseases that these bats can carry and transfer (including rabies) they were culled after European settlers reached South America. I think that the introduction of farm animals to the region enabled vampire bats to prey on larger and more abundant animals, but the hunting of the animals prevented them from spreading over great distances. I can't find any information on the evolution of the bats, but there are many carnivorous bats found in these regions. Their specialised diet probably evolved after the Gondwanan continent broke apart, making it difficult for the bat (and therefore this feature) to spread to these regions.
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