Platypus venom

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. Venom is primarily made during mating season.[1] While the venom's effects are described as excruciatingly 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 character 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]

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

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 connected by a thin-walled duct to a calcaneus 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; superadded by 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]

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 – although some muscle wastage has been observed in cases of envenomation in humans, it is likely that this is 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 whether the venom has a component that acts directly on the pain receptors.

Although platypus venom has a broadly similar range of effects and is known to consist of a similar selection of substances to reptilian venom, it appears to have a different function from those poisons produced by lower vertebrates; its 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 nor killing prey, and although it acts as a defensive mechanism, only males produce venom. Since production rises during the breeding season it is theorised that it is used as an offensive weapon to assert dominance and control territory during this period.[4]

Effect on humans and other animals

Although powerful enough to paralyse smaller animals,[4] the venom is not lethal to humans. However, it produces excruciating pain that may be intense enough to incapacitate the 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][9] A clinical report from 1992 showed that the severe pain was persistent and did not respond to morphine.

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. One 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.[10]

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See also

References
  1. Whittington, C. M.; Papenfuss, A. T.; Bansal, P.; Torres, A. M.; Wong, E. S. W.; Deakin, J. E.; Graves, T.; Alsop, A.; Schatzkamer, K.; Kremitzki, C.; Ponting, C. P.; Temple-Smith, P.; Warren, W. C.; Kuchel, P. W.; Belov, K. (2008). "Defensins and the convergent evolution of platypus and reptile venom genes". Genome Research. 18 (6): 986–94. doi:10.1101/gr.7149808. PMC 2413166. PMID 18463304.
  2. Jørn H. Hurum, Zhe-Xi Luo, and Zofia Kielan-Jaworowska, Were mammals originally venomous?, Acta Palaeontologica Polonica 51 (1), 2006: 1-11
  3. Grant, J. R. "Fauna of Australia chap.16 vol.1b" (PDF). Australian Biological Resources Study (ABRS). Archived from the original (PDF) on 20 October 2013. Retrieved 13 December 2006.
  4. Gerritsen, Vivienne Baillie (December 2002). "Platypus poison". Protein Spotlight (29). Retrieved 13 December 2006.
  5. "The venom of the platypus (Ornithorhynchus anatinus)". kingsnake.com. Archived from the original on 1 February 2012.
  6. De Plater, G.; Martin, R. L.; Milburn, P. J. (1995). "A pharmacological and biochemical investigation of the venom from the platypus (Ornithorhynchus anatinus)". Toxicon. 33 (2): 157–69. doi:10.1016/0041-0101(94)00150-7. PMID 7597719.
  7. Warren, W. C.; Hillier, L. W.; Marshall Graves, J. A.; Birney, E.; Ponting, C. P.; Grützner, F.; Belov, K.; Miller, W.; Clarke, L.; Chinwalla, A. T.; Yang, S. P.; Heger, A.; Locke, D. P.; Miethke, P.; Waters, P. D.; Veyrunes, F. D. R.; Fulton, L.; Fulton, B.; Graves, T.; Wallis, J.; Puente, X. S.; López-Otín, C.; Ordóñez, G. R.; Eichler, E. E.; Chen, L.; Cheng, Z.; Deakin, J. E.; Alsop, A.; Thompson, K.; Kirby, P. (2008). "Genome analysis of the platypus reveals unique signatures of evolution". Nature. 453 (7192): 175–183. doi:10.1038/nature06936. PMC 2803040. PMID 18464734.
  8. Torres, A. M.; Menz, I.; Alewood, P. F.; Bansal, P.; Lahnstein, J.; Gallagher, C. H.; Kuchel, P. W. (2002). "D-Amino acid residue in the C-type natriuretic peptide from the venom of the mammal, Ornithorhynchus anatinus, the Australian platypus". FEBS Letters. 524 (1–3): 172–6. doi:10.1016/S0014-5793(02)03050-8. PMID 12135762.
  9. De Plater, G. M.; Milburn, P. J.; Martin, R. L. (2001). "Venom from the platypus, Ornithorhynchus anatinus, induces a calcium-dependent current in cultured dorsal root ganglion cells" (PDF). Journal of Neurophysiology. 85 (3): 1340–1345. doi:10.1152/jn.2001.85.3.1340. PMID 11248005.
  10. Grant, Tom (2007). Platypus. Melbourne: CSIRO Publishing. pp. 41–42. ISBN 9780643093706.
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