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Dendroaspis

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Dendroaspis
A Jameson's mamba
A Jameson's mamba
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Reptilia
Order: Squamata
Suborder: Serpentes
Family: Elapidae
Subfamily: Elapinae
Genus: Dendroaspis
Schlegel, 1848
Species

Dendroaspis (literally meaning "tree snake"), or more commonly known as mambas is a genus or a group of highly venomous, fast-moving land-dwelling snakes endemic to the continent of Africa. They, like the cobras, kraits, coral snakes, and the Australian elapids, also belong to the family Elapidae. Mambas are feared throughout their ranges in Africa, especially the Black mamba. In Africa, there are many legends and stories describing these snakes.

Behavior

Most of the members of this genus (for example green mambas) are arboreal. However, the black mamba is terrestrial. They are all diurnal. During the day, they actively hunt their prey of small mammals, birds, and lizards, and return to the same lair nightly. Black mambas average around 3.2 m (10.5 ft) in length and may grow up to 4.45 m (14.6 ft), so they can eat larger prey items than can the other mamba species. For example, black mambas can eat chickens and blue duiker (Philantomba monticola).[1]

Mambas are related to the cobras (Elapidae); their threat display, when they stretch a slightly smaller "hood" while gaping their mouth, is similar. This trait is most prominent in the black mamba.

Many people believe that the black mamba will chase and attack humans. However, this is probably misunderstood because of the speed with which this species can move.[2] The black mamba usually uses its speed to escape from threats. Humans are actually their main predators, rather than their prey; mambas generally avoid contact with humans.

Venom

All mambas are highly venomous. Their venoms consist mostly of neurotoxins (known as dendrotoxins). Besides the neurotoxins, they also carry cardiotoxins[3] and fasciculins. Other components may include calcicludine, which is a known component of the eastern green mamba's venom and calciseptine, which is a component of black mamba venom. Toxicity of individual specimens within the same species and subspecies can vary greatly based on several factors, including geographical region. A bite can be fatal to humans without access to proper first aid and subsequent antivenom treatment, as it shuts down the lungs and heart. The western green mamba (D. viridis), eastern green mamba (D. angusticeps), and Jameson's mamba (D. jamesoni) possess venom similar in composition and effects to that of the black mamba's (D. polylepis). However, as their venoms are less toxic (based upon Template:LD50 studies), their temperaments are generally not as aggressive or as explosive when provoked, and none of the three inject as much venom as the black mamba, their bites are materially less dangerous.

Prior to the availability of antivenom, envenomations by members of this genus carried a high fatality rate. An untreated black mamba bite has a mortality rate of 100%,[4][5][6][7] but presently, fatalities have become much rarer due to wide availability of antivenom.

Mamba toxins

Mamba toxin (or dendrotoxin) consists of several components, with different targets. Examples are:

  • Dendrotoxin 1, which inhibits the K+ channels at the pre and post-synaptic level in the intestinal smooth muscle. It also inhibits Ca2+-sensitive K+ channels from rat skeletal muscle‚ incorporated into planar bilayers (Kd = 90 nM in 50 mM KCl).[8])
  • Dendrotoxin 3, which inhibits acetylcholine M4 receptors.[9]
  • Dendrotoxin 7, commonly referred to as muscarinic toxin 7 (MT7) inhibits acetylcholine M1 receptors.[9]
  • Dendrotoxin K, structually homologous to Kunitz-type proteinase inhibitors [10] with activity as a selective blocker of voltage-gated potassium channels [11]

Species

Species[12] Authority[12] Subsp.*[12] Common name Geographic range
Dendroaspis angusticeps (Smith, 1849) 0 Eastern green mamba Found in Kenya, Tanzania, Malawi, Mozambique, Zimbabwe, Swaziland, Namibia, western South Africa, Democratic Republic of the Congo, South Sudan, Sudan, Niger, Central African Republic, Chad
Dendroaspis jamesoni (Traill, 1843) 2 Jameson's mamba Found in Central Africa in Sudan, South Sudan, Gabon, Angola, Zambia, Republic of the Congo, Cameroon, Nigeria, Kenya, Uganda, Rwanda, Central African Republic, Benin, Ghana
Dendroaspis polylepis Günther, 1864 0 Black mamba Found in eastern Africa and southern Africa in northeast Democratic Republic of the Congo, southwestern Sudan to Ethiopia, Eritrea, Somalia, Kenya, eastern Uganda, Tanzania, southwards to Mozambique, Swaziland, Malawi, Zambia, Zimbabwe, Lesotho, Rwanda, Djibouti and Botswana to KwaZulu-Natal in South Africa, and Namibia; then northeasterly through Angola to the southeastern part of the Democratic Republic of Congo
Dendroaspis viridis (Hallowell, 1844) 0 Western green mamba Found only in western Africa in southern Senegal, Gambia, Guinea-Bissau, Guinea, Sierra Leone, Liberia, Côte d’Ivoire, Ghana, Togo, Benin, and southwest Nigeria

* Including the nominate subspecies.


Cited references

  1. Marais, Johan. (2004). A Complete Guide to the Snakes of Southern Africa. Cape Town, South Africa: Struik Nature. 95-97 pp. ISBN 1-86872-932-X.
  2. Halliday, Tim. (2002). Firefly Encyclopedia of Reptiles and Amphibians. Firefly Books. ISBN 1552976130
  3. (May 1996) "Putative cardiotoxicity of the venoms of three mamba species.". Journal of Wilderness and Environmental Medicine 7 (2): 115–21. PMID 11990104.
  4. Mortality Rate at Sean Thomas. Accessed 19 May 2012.
  5. Nature-Black Mamba
  6. Black Mamba Intro
  7. Davidson, Terence. IMMEDIATE FIRST AID. University of California, San Diego. Retrieved on 2011-09-22.
  8. (1991) "[Potassium channels and epilepsy: evidence that the epileptogenic toxin, dendrotoxin, binds to potassium channel proteins.]". Epilepsy Research Supplement 4: 263–73.. PMID 1815606.
  9. 9.0 9.1 Rang, H. P. (2003). Pharamacology. Edinburgh: Churchill Livingstone, 139. ISBN 0-443-07145-4. 
  10. (5 December 1993) "[Nuclear magnetic resonance solution structure of dendrotoxin K from the venom of Dendroaspis polylepis polylepis.]". Journal of Molecular Biology 234 (3): 735–50. PMID 8254670.
  11. (2004) "Dendrotoxins: structure-activity relationships and effects on potassium ion channels.". Curr Med Chem. 23: 3065–72.. PMID 15579000.
  12. 12.0 12.1 12.2 Dendroaspis (TSN 700211) at Integrated Taxonomic Information System. Accessed 19 May 2012.