Venomous Australian Mammals

Monotremes are egg-laying mammals that are only found in Australia and New Guinea. The only extant monotremes are the platypus and the four species of echidnas. Playtpi live in fresh water rivers and streams along the East Coast of Australia. They have a spur on their hind legs that delivers the venom. Both males and females are born with these spurs, but females lose them during development. Male platypi use their spurs (and venom) to fight with one another to compete for females. Whilst fighting, the males puncture one another with their spurs and inject each other with venom. During the mating season, the crural glands and testicles increase in size, and the crural glands become highly active, producing venom to be delivered by the spur. Platypus envenomation was first recorded in the early 1800s. Envenomation results in immediate and acute pain and swelling. The only effective treatment is localised anaesthetic, but even then symptoms can last from two weeks to several months. In the venom, there are 88 venom genes, many of which are similar to the venom genes of reptiles, insectivores, fish and invertebrates. The peptides in the venom affect the blood pressure and disrupt ion transport pathways of the victim (Ligabue-Braun, Verli, & Carlini, 2012).

A platypus (Image 1).

A diagram of the venom system of a platypus (Image 2).

Echidnas have a very similar system, but they do not use it in the same way that the platypus does. Both male and females have degenerate spurs, like the female platypus. During the mating season, the male glands undergo change consistent with their levels of sexual hormones. The poor mechanism for locking the spur the the tibia during an attack suggests that the spur is not used as a weapon. Instead, it is thought that glands produce a scent that the male echidnas use to attract a mate (Ligabue-Braun, Verli, & Carlini, 2012).

An echidna (Image 3).

References

Ligabue-Braun, R., Verli, H., & Carlini, C. R. (2012). Venomous Mammals: A Review. Toxicon , 59, 680-695.

Images

Image 1 - http://www.amamoorlodge.com.au/images/platypus-03-swimming.jpg. Accessed on 24/4/14.

Image 2 - http://cf067b.medialib.glogster.com/media/06/060707b4736bd3395eef00ae83734935c283f845ed1ec7a04cd5603b95ba1995/platypus-spur-png.png. Accessed on 22/4/14.

Image 3 - http://answersafrica.com/wp-content/uploads/2013/10/echidna11.jpg. Accessed on 24/4/14.