Mamba
Mamba | |
---|---|
Black mamba | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Order: | Squamata |
Suborder: | Serpentes |
Family: | Elapidae |
Subfamily: | Elapinae
|
Genus: | Dendroaspis Schlegel, 1848[1] |
Species | |
| |
D. polylepis
D. angusticeps
D. viridis
|
Mambas are fast-moving, highly
Behaviour
The three green species of mambas are
Stories of black mambas that chase and attack humans are common, but in fact the snakes generally avoid contact with humans.[5] The black mamba (Dendroaspis polylepis) is a highly venomous snake species native to various parts of sub-Saharan Africa. Black mambas are fast-moving, nervous snakes that will strike when threatened. According to findings by Branch (2016), their venom comprises neurotoxins and cardiotoxins that can rapidly induce symptoms, including dizziness, extreme fatigue, vision problems, foaming at the mouth, paralysis, convulsions, and eventual death from respiratory or cardiac failure if untreated. Although black mamba venom is highly toxic, antivenom is available and can treat envenomation promptly.
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
All mambas have
There are multiple components in dendrotoxins with different targets:
- 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).[10])
- Dendrotoxin 3, which inhibits M4 receptors.[11]
- Dendrotoxin 7, commonly referred to as M1 receptors.[11]
- Dendrotoxin K, structurally homologous to Kunitz-type proteinase inhibitors[12] with activity as a selective blocker of voltage-gated potassium channels[13]
Toxicity alone does not determine severity of envenomation; other factors include the snake's temperament, venom yields, proximity of wounds to the CNS and depth of punctures.[14] Bites by all members of this genus are capable of causing rapid onsets of symptoms, but it is the black mamba whose bite has the worst prognosis, possibly as a result of its more terrestrial nature (having more potential for human contact), high defensiveness (having a higher possibility to deliver fatal bites instead of dry bites), large size (giving it a higher strike position proximal to the victim's brain), and higher average venom yields and potential toxicity (based on experimental results).[15][16] A lethality rate of near 100% for untreated black mamba bites has been circulating between various sources,[16] which is probably based on a single medical record made in a single district between 1957 and 1963 when specific antivenom had yet to be introduced. Seven out of seven victims of this species who received non-specific polyvalent antivenom, that had no effect on the species' toxins, succumbed to its bites.[5] However, another snakebite survey in South Africa reported a death rate of approximately 43% among those who received ineffective treatments (15 fatal cases out of 35 patients).[17] A mamba-specific antivenom was introduced in 1962, followed by a fully polyvalent antivenom in 1971; over this period, 5 out of 38 people in South Africa bitten by black mambas who received the antivenom died, according to the same report.[17] Since then, the number has significantly dropped with the widespread use of specific antivenom.[18][17]
Despite their fearsome reputation and often exaggerated notoriety, mamba envenomation occurs far less frequently than some other snakes', for instance the
Taxonomy
Dendroaspis, is derived from Ancient Greek déndron (δένδρον), meaning "tree",[19] and aspis (ασπίς), which is understood to mean "shield",[20] but also denotes "cobra" or simply "snake", in particular "snake with hood (shield)". Via Latin aspis, it is the source of the English word "asp". In ancient texts, aspis or asp often referred to the Egyptian cobra (Naja haje), in reference to its shield-like hood.[21] The genus was first described by the German naturalist Hermann Schlegel in 1848,[22] with Elaps jamesonii as the type species. It was misspelt as Dendraspis by Dumeril in 1856, and generally uncorrected by subsequent authors. In 1936, Dutch herpetologist Leo Brongersma pointed out that the correct spelling was Dendroaspis but added that the name was invalid as Fitzinger had coined Dendraspis in 1843 for the king cobra and hence had priority.[23] However, in 1962 German herpetologist Robert Mertens proposed that the 1843 description of Dendraspis by Fitzinger be suppressed due to its similarity to Dendroaspis, and the confusion it would cause by its use.[24]
Range and characteristics
Black mambas live in the savannas and rocky hills of southern and eastern Africa. They are Africa's longest venomous snake, reaching up to 14 feet in length, although 8.2 feet is more the average. They are also among the fastest snakes in the world, slithering at speeds of up to 12.5 miles per hour.[2][6]
* Including the nominate subspecies.
T Type species.
Phylogeny
A 2018 analysis of the venom of the mambas, as well as a 2016 genetic analysis, found the following cladogram representative of the relationship between the species.[26][27]
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Notes
- ^ Snakes of medical importance include those with highly dangerous venom resulting in high rates of morbidity and mortality, or those that are common agents in snakebite.[9]
- ^ A binomial authority in parentheses indicates that the species was originally described in a genus other than Dendroaspis.
References
- ^ "Dendroaspis". Integrated Taxonomic Information System. Retrieved 30 October 2012.
- ^ a b c d "National Geographic (Black Mamba, Dendroaspis polylepis)". National Geographic Society. 10 September 2010. Archived from the original on May 30, 2017. Retrieved 17 October 2020.
African myths exaggerate their capabilities to legendary proportions; Black mambas are shy and will almost always seek to escape when confronted.
- ISBN 90-04-07455-4.
- ^ Alfred Burdon Ellis (1887). South African Sketches. Chapman and Hall, Limited. also at: [1]
- ^ 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
- ^ a b The new encyclopedia of Reptiles (Serpent). Time Book Ltd. 2002.
- ^ "Neurotoxins in Snake Venom". Retrieved 2019-12-26.
- PMID 11990104.
- ^ a b WHO Expert Committee on Biological Standardization. "Guidelines for the production, control and regulation of snake antivenom immunoglobulins" (PDF). WHO Technical Report Series, No. 964. pp. 224–226. Retrieved 1 January 2019.
- PMID 1815606.
- ^ ISBN 0-443-07145-4.
- PMID 8254670.
- PMID 15579000.
- ISBN 9781351443142.
- ^ Séan Thomas & Eugene Griessel – Dec 1999. "LD50 (Archived)". Archived from the original on 1 February 2012.
{{cite web}}
: CS1 maint: numeric names: authors list (link) - ^ a b c Branch, W (January 1979). "The venomous snakes of Southern Africa Part 2. Elapidae and Hydrophidae". The Snake. 11 (2): 199–225. Retrieved 1 July 2021.
- ^ PMID 7244896.
- S2CID 40171925.
- ^ "dendro-". Collins English Dictionary - Complete & Unabridged 10th Edition. HarperCollins Publishers. Retrieved 4 March 2014.
- ^ "Definition of "aspis" - Collins English Dictionary". collinsdictionary.com. Retrieved 15 February 2015.
- ^ "aspis, asp". Dictionary.com Unabridged. Random House. Retrieved 4 March 2014.
- ^ "Dendroaspis". Integrated Taxonomic Information System. Retrieved 9 December 2013.
- ^ Brongersma, Leo Daniel (1936). "Herpetological note XIII". Zoo. Mededeel. 19: 135.
- ^ Mertens, Robert (1962). "Dendraspis Fitzinger, 1843 (Reptilia, Serpentes); Proposed Suppression under the Plenary Powers. Z.N. (S.) 1500" (PDF). Bulletin of Zoological Nomenclature. 19: 189–190.
- ^ a b c "Dendroaspis". Integrated Taxonomic Information System. Archived from the original on 12 March 2009. Retrieved 5 July 2013.
- S2CID 217018550.
- PMID 27603205.
- ISSN 0041-0101.