Platypus venom

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The venom-delivering spur is found only on the male's hind limbs. Platypus spur.JPG
The venom-delivering spur is found only on the male's hind limbs.

The platypus is one of the few living mammals to produce venom. The venom is made in venom glands that are connected to hollow spurs on their hind legs; it is primarily made during the mating season. [1] While the venom's effects are described as extremely painful, it is not lethal to humans. Many archaic mammal groups possess similar tarsal spurs, so it is thought that, rather than having developed this characteristic uniquely, the platypus simply inherited this characteristic from its antecedents. Rather than being a unique outlier, the platypus is the last demonstration of what was once a common mammalian characteristic, and it can be used as a model for non-therian mammals and their venom delivery and properties. [2]

Contents

Spur and crural gland

The venom is produced in the crural glands of the male, which are kidney-shaped alveolar glands located in the upper thigh, and delivered through a spur, or calcar, on each hind limb. Female platypuses, in common with echidnas, have rudimentary spur buds that do not develop (dropping off before the end of their first year) and lack functional crural glands. [3] The spur is attached to a small bone that allows articulation; the spur can move at a right angle to the limb allowing a greater range of attack than a fixed spur would allow. [4] The spur normally lies flat against the limb but is raised when required. [5]

Venom

The crural gland produces a venom secretion containing at least nineteen peptides and some non-nitrogenous components. [6] Those peptides that have been sequenced and identified fall into three categories: defensin-like peptides (OvDLPs), C-type natriuretic peptides (OvCNPs), and nerve growth factor (OvNGF). [1] The OvDLPs are related to, though distinct from, those involved in reptilian venom production. [7] This appears to be an example of convergent evolution of venom genes from existing immune system genes (defensins). [1] A unique feature of the venom is the presence of a D-amino acid. This is the only known such example in mammalian systems. [8] This venom appears to be related to that of several species that are not part of the platypus's evolutionary lineage, such as certain fish, reptiles, insectivores, and spiders, sea anemones, and starfish. [9]

The different chemicals in the venom have a range of effects from lowering blood pressure to causing pain and increasing blood flow around the wound. [4] Coagulating effects have been seen during experiments on laboratory animals, but this has not been observed consistently. Unlike snake venom, there appears to be no necrotising component in the platypus's venom. While some muscle wastage has been observed in cases of envenomation in humans, it is likely due to the inability to use the limb while the effects of the venom persist. [5] It is unknown whether the pain caused is a result of the associated edema around the wound or the venom has a component that acts directly on the pain receptors.

The platypus venom has a broadly similar range of effects and is known to consist of a similar selection of substances to reptilian venom, and appears to have a different function from those poisons produced by lower vertebrates. The effects are not life-threatening but nevertheless powerful enough to cause serious impairment to the victim, which can lead to temporary paralysis. It is not used as a method of disabling or killing prey, more as a defensive mechanism. Only males produce this venom. Since production rises during the breeding season, it is theorised that the venom is used as an offensive weapon to assert dominance and to control territory during this period. [4] While the platypus may use this characteristic for offensive mating purposes, they may have also adapted it for defensive techniques. Crocodiles, Tasmanian devils and raptors are known local predators to the platypus, all of which can be impacted by the venom. [10] [11]

Effect on humans and other animals

Although powerful enough to paralyse smaller animals, [4] the venom is not lethal to humans. Yet, it produces excruciating pain that may be intense enough to incapacitate a victim. Swelling rapidly develops around the entry wound and gradually spreads outward. Information obtained from case studies shows that the pain develops into a long-lasting hyperalgesia that can persist for months but usually lasts from a few days to a few weeks. [5] [12] A clinical report from 1992 showed that the severe pain was persistent and did not respond to morphine. [13]

In 1991 Keith Payne, a former member of the Australian Army and recipient of the Victoria Cross (Australia's highest award for valour), was struck on the hand by a platypus spur while trying to rescue the stranded animal. He described the pain as worse than being struck by shrapnel. A month later he was still experiencing pain in that hand. In 2006, Payne reported discomfort and stiffness when carrying out some physical activities such as using a hammer. [14]

See also

Related Research Articles

<span class="mw-page-title-main">Platypus</span> Species of mammal

The platypus, sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania. The platypus is the sole living representative or monotypic taxon of its family Ornithorhynchidae and genus Ornithorhynchus, though a number of related species appear in the fossil record.

Peptides are short chains of amino acids linked by peptide bonds. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides which have a molecular mass of 10,000 Da or more are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides.

<span class="mw-page-title-main">Venom</span> Toxin secreted by an animal

Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved venom apparatus, such as fangs or a stinger, in a process called envenomation. Venom is often distinguished from poison, which is a toxin that is passively delivered by being ingested, inhaled, or absorbed through the skin, and toxungen, which is actively transferred to the external surface of another animal via a physical delivery mechanism.

<span class="mw-page-title-main">Ornithorhynchidae</span> Family of monotremes

The Ornithorhynchidae are one of the two extant families in the order Monotremata, and contain the platypus and its extinct relatives. The other family is the Tachyglossidae, or echidnas. Within the Ornithorhynchidae are the genera Monotrematum, Obdurodon, and Ornithorhynchus:

<span class="mw-page-title-main">Stinger</span> Sharp organ capable of injecting venom

A stinger is a sharp organ found in various animals capable of injecting venom, usually by piercing the epidermis of another animal.

<i>Steropodon</i> Extinct genus of monotremes

Steropodon is a genus of prehistoric platypus-like monotreme, or egg-laying mammal. It contains a single species, Steropodon galmani, that lived about 105 to 93.3 million years ago (mya) during the Cretaceous period, from early to middle Cenomanian. It is one of the oldest monotremes discovered, and is one of the oldest Australian mammal discoveries.

<span class="mw-page-title-main">Snake venom</span> Highly modified saliva containing zootoxins

Snake venom is a highly toxic saliva containing zootoxins that facilitates in the immobilization and digestion of prey. This also provides defense against threats. Snake venom is injected by unique fangs during a bite, whereas some species are also able to spit venom.

<span class="mw-page-title-main">Hyperalgesia</span> Abnormally increased sensitivity to pain

Hyperalgesia is an abnormally increased sensitivity to pain, which may be caused by damage to nociceptors or peripheral nerves and can cause hypersensitivity to stimulus. Prostaglandins E and F are largely responsible for sensitizing the nociceptors. Temporary increased sensitivity to pain also occurs as part of sickness behavior, the evolved response to infection.

<span class="mw-page-title-main">Melittin</span> Chemical compound

Melittin is the main component and the major pain-producing substance of honeybee venom. Melittin is a basic peptide consisting of 26 amino acids.

<span class="mw-page-title-main">Defensin</span> Group of antimicrobial peptides

Defensins are small cysteine-rich cationic proteins across cellular life, including vertebrate and invertebrate animals, plants, and fungi. They are host defense peptides, with members displaying either direct antimicrobial activity, immune signaling activities, or both. They are variously active against bacteria, fungi and many enveloped and nonenveloped viruses. They are typically 18-45 amino acids in length, with three or four highly conserved disulphide bonds.

<span class="mw-page-title-main">Spitting cobra</span> Common name for several snakes

A ”spitting” cobra is any of several species of cobra that can intentionally, defensively shoot their venom directly from their fangs. This substance has two functions, with the first being as venom that can be absorbed via the victim’s eyes, mouth, or nose, and secondly as a toxungen, which can be sprayed on the target surface. Their ability to target and shoot venom is utilised in several different ways, self-defense being the most common instance. Studies have shown that the targets are far from random; rather, spitting cobras consciously take aim, directing their spray as close as possible to the eyes and face of an aggressor.

<span class="mw-page-title-main">Venomous mammal</span> Venom-producing animals of the class Mammalia

Venomous mammals are animals of the class Mammalia that produce venom, which they use to kill or disable prey, to defend themselves from predators or conspecifics or in agonistic encounters. Mammalian venoms form a heterogeneous group with different compositions and modes of action, from three orders of mammals: Eulipotyphla, Monotremata, and Chiroptera. It has been proposed that some members of a fourth order, Primates, are venomous. To explain the rarity of venom delivery in Mammalia, Mark Dufton of the University of Strathclyde has suggested that modern mammalian predators do not need venom because they are able to kill quickly with their teeth or claws, whereas venom, no matter how sophisticated, requires time to disable prey.

<i>Akidolestes</i> Extinct genus of mammals

Akidolestes is an extinct genus of mammals of the family Spalacotheriidae, a group of mammals related to therians.

<span class="mw-page-title-main">Myotoxin</span>

Myotoxins are small, basic peptides found in snake venoms and lizard venoms. This involves a non-enzymatic mechanism that leads to severe muscle necrosis. These peptides act very quickly, causing instantaneous paralysis to prevent prey from escaping and eventually death due to diaphragmatic paralysis.

<span class="mw-page-title-main">Beta defensin</span>

Beta defensins are a family of vertebrate defensins. The beta defensins are antimicrobial peptides implicated in the resistance of epithelial surfaces to microbial colonization.

<span class="mw-page-title-main">Plant defensin</span>

Plant defensins are a family of primitive, highly stable, cysteine-rich defensins found in plants that function to defend them against pathogens and parasites. Defensins are integral components of the innate immune system and belong to the ancient superfamily of antimicrobial peptides (AMPs). AMPs are also known as host defense peptides (HDPs), and they are thought to have diverged about 1.4 billion years ago before the evolution of prokaryotes and eukaryotes. They are ubiquitous in almost all plant species, functionally diverse, and their primary structure varies significantly from one species to the next, except for a few cysteine residues, which stabilize the protein structure through disulfide bond formation. Plant defensins usually have a net positive charge due to the abundance of cationic amino acids and are generally divided into two classes. Those in the class II category contain a C-terminal pro-peptide domain of approximately 33 amino acids and are targeted to the vacuole, while the class I defensins lack this domain and mature in the cell wall. Unlike their class I counterparts, class II plant defensins are relatively smaller, and their acidic C-terminal prodomain is hypothesized to contribute to their vacuolar targeting. The first plant defensins were discovered in barley and wheat in 1990 and were initially designated as γ-thionins. In 1995, the name was changed to 'plant defensin' when it was identified that they are evolutionarily unrelated to other thionins and were more similar to defensins from insects and mammals.

<span class="mw-page-title-main">Monotreme</span> Order of egg-laying mammals

Monotremes are mammals of the order Monotremata. They are the only known group of living mammals that lay eggs, rather than bearing live young. The extant monotreme species are the platypus and the four species of echidnas. Monotremes are typified by structural differences in their brains, jaws, digestive tract, reproductive tract, and other body parts, compared to the more common mammalian types. Although they are different from almost all mammals in that they lay eggs, like all mammals, the female monotremes nurse their young with milk.

Ergtoxin is a toxin from the venom of the Mexican scorpion Centruroides noxius. This toxin targets hERG potassium channels.

<small>D</small>-Amino acid Class of chemical compounds

ᴅ-Amino acids are amino acids where the stereogenic carbon alpha to the amino group has the ᴅ-configuration. For most naturally-occurring amino acids, this carbon has the ʟ-configuration. ᴅ-Amino acids are occasionally found in nature as residues in proteins. They are formed from ribosomally-derived ᴅ-amino acid residues.

References

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