Mamba
| Dendroaspis | |
|---|---|
 |
|
| Black mamba | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Subphylum: | Vertebrata |
| Class: | Reptilia |
| Order: | Squamata |
| Suborder: | Serpentes |
| Family: | Elapidae |
| Genus: | Dendroaspis Schlegel, 1848 [1] |
| Species | |
Mambas are fast-moving venomous snakes of the genus Dendroaspis (which literally means "tree asp") in the family Elapidae. Four extant species are recognised currently; three of those four species are essentially arboreal and green in colour, whereas the so-called black mamba, Dendroaspis polylepis, is largely terrestrial and generally brown or grey in colour. All are native to various regions in sub-Saharan Africa and all are feared throughout their ranges, especially the black mamba. In Africa there are many legends and stories about mambas.[2][3][4]
Behaviour[edit]
The three species of green mambas are arboreal, whereas the black mamba is largely terrestrial. All four species are active diurnal hunters, preying on birds, lizards, and small mammals. At nightfall some species, especially the terrestrial black mamba, shelter in a lair. A mamba may retain the same lair for years.
Mambas and cobras are in the same family: the Elapidae. Like cobras, a mamba may rear and form a hood as part of its threat display, but the mamba's hood is narrower and is longer than the broader hood of some species of cobra, such as say, the spectacled cobras of parts of Asia. In their threat display mambas commonly gape; the black mamba's mouth is black within, which renders the threat more conspicuous. Typically also, a rearing mamba tends to lean well forward, instead of standing erect as a cobra does.
Stories of black mambas that chase and attack humans are common, but in fact the snakes generally avoid contact with humans.[5] Most apparent cases of pursuit probably are examples of where witnesses have mistaken the snake's attempt to retreat to its lair when a human happens to be in the way.[6] The black mamba usually uses its speed to escape from threats, and humans actually are their main predators, rather than prey.[2]
Venom[edit]
All mambas are highly venomous. Their venoms consist mostly of neurotoxins (known as dendrotoxins). Besides the neurotoxins, they also carry cardiotoxins[2][7] and fasciculins.[8][9] 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. Even the weather and altitude can influence toxicity (Ernst and Zug et al. 1996). 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 LD50 studies), and their temperaments generally not as aggressive or as explosive when provoked, and as none of the three injects as much venom as the black mamba, their bites are materially less dangerous.[citation needed]
Prior to the availability of antivenom, envenomations by members of this genus carried a high fatality rate. Untreated black mamba bites have a mortality rate of 100%,[5][10] but presently, fatalities have become much rarer due to wide availability of antivenom.
Mamba toxins[edit]
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).[11])
- Dendrotoxin 3, which inhibits acetylcholine M4 receptors.[12]
- Dendrotoxin 7, commonly referred to as muscarinic toxin 7 (MT7) inhibits acetylcholine M1 receptors.[12]
- Dendrotoxin K, structurally homologous to Kunitz-type proteinase inhibitors [13] with activity as a selective blocker of voltage-gated potassium channels [14]
Species[edit]
- Of the currently recognised mamba species, three are green and the other is the "black mamba", so called in spite of its generally brown or grey body.
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* Including the nominate subspecies.
T Type species.
References[edit]
- ^ "Dendroaspis". Integrated Taxonomic Information System. Retrieved 30 October 2012.
- ^ a b c "National Geographic (Black Mamba, Dendroaspis polylepis)". National Geographic Society. Retrieved 5 July 2013.
African myths exaggerate their capabilities to legendary proportions; Black mambas are shy and will almost always seek to escape when confronted.
- ^ Jan Knappert (1 January 1985). Myths and Legends of Botswana, Lesotho, and Swaziland. Brill Archive. pp. 53–. ISBN 90-04-07455-4.
- ^ Alfred Burdon Ellis (1887). South African Sketches. Chapman and Hall, Limited. also at: [1]
- ^ a b O'Shea, Mark (2005). VENOMOUS SNAKES OF THE WORLD. multiple places: US and Canada: Princeton University Press; Europe: New Holland (UK) Ltd. pp. 78–79. ISBN 978-0-691-15023-9.
...in common with other snakes they prefer to avoid contact;...Of the three species of green mambas...;...from 1957 to 1963...including all seven black mamba bites - a 100 per cent fatality rate
- ^ The new encyclopedia of Reptiles (Serpent). Time Book Ltd. 2002.
- ^ van Aswegen G, van Rooyen JM, Fourie C, Oberholzer G. (May 1996). "Putative cardiotoxicity of the venoms of three mamba species.". Journal of Wilderness and Environmental Medicine. 7 (2): 115–21. doi:10.1580/1080-6032(1996)007[0115:PCOTVO]2.3.CO;2. PMID 11990104.
- ^ Fasciculin
- ^ Neurotoxins in Snake Venom
- ^ Davidson, Terence. "IMMEDIATE FIRST AID". University of California, San Diego. Retrieved 2011-09-22.
- ^ Newitt RA, Houamed KM, Rehm H, Tempel BL. (1991). "[Potassium channels and epilepsy: evidence that the epileptogenic toxin, dendrotoxin, binds to potassium channel proteins.]". Epilepsy Research Supplement. 4: 263–73. PMID 1815606.
- ^ a b Rang, H. P. (2003). Pharmacology. Edinburgh: Churchill Livingstone. p. 139. ISBN 0-443-07145-4.
- ^ Berndt KD, Güntert P, Wüthrich K. (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. doi:10.1006/jmbi.1993.1623. PMID 8254670.
- ^ Harvey AL, Robertson B. (2004). "Dendrotoxins: structure-activity relationships and effects on potassium ion channels.". Curr Med Chem. 23: 3065–72. doi:10.2174/0929867043363820. PMID 15579000.
- ^ a b c "Dendroaspis". Integrated Taxonomic Information System. Retrieved 5 July 2013.
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