Adding It Up

Australia is home to some of the world’s most beautiful and deadly snakes.  There are currently 93 Species of Elapid in Australia. Elapids are classified usually by their short fixed fangs at the front of their mouth. Elapids are a extremely diverse group of snakes. Ranging from the nitrious 5 meter King cobra (Ophiophagus hannah) found in India, to the 40cm Small eyed snake (Rhinoplocephalus nigrescens) found on the east coast of Australia. Most of which are found here in Australia are long, slender, extremely fast moving and very alert snakes. Remaining active during the day moving constantly to find food. However there is a Genus of Elapid which is slightly unique in their appearance and behavior, these are the Acanthophis species or death adders.  There are currently 4 species of death adder in Australia along with a small number of other species found in Papa New Guinea. 

Photo by Ryan Pilgrim

Pilbara Death Adder

Acanthophis wellsi

Death adders belong to the Elapid family however at first glance they would appear to be more at home with the Vipers. They resemble the European adders, Puff adders and other viper species, they are short stout snakes not well adapted for traveling long distances in search of food but instead have evolved to become effective ambush predators. Death adders will bury themselves in the leaf litter or sand and wait patiently for prey to come to them. There have evolved a lure at the end of the tail which they leave exposed and wriggling in order to entice a small animal closer. They possess a lightning fast strike which has been measured at 0.2 of second from a standing ambush position to the target. This tactic of sit and wait in ambush is common throughout the viper family and a number of species which also use this caudal luring technique to attract prey.

Puff Adder

 Bitis arietans

http://www.venomousreptiles.org/classifieds/detail/12133

28/4/14 18:37 

 Photo by Ryan Pilgrim

Common Death Adder

Acanthophis  antarcticus

It is clear that this is an excellent example of convergent evolution at work. There are no vipers in Australia, this indicated the death adders have independently evolved this style of prey capture alongside vipers found all across the globe. Death adders produce a neurotoxic venom which can affect the nervous system and symptoms relate to neuromuscular failure leading to paralysis and breathing failure. This is where the similarities end as vipers possess a haemotoxic venom which attacks red blood cells either causing serious haemorrhaging or clotting of the blood this causes multiple organ failure and commonly necrosis at the bit site.

 Photo by Ryan Pilgrim

Albino Northern Death Adder

 Acanthophis praelongus

 References:

Shine, R 1980, “Ecology of the Australian death adder Acanthophis antarcticus (elapidae): evidence for convergence with the viperidae”, Herpetological, vol. 36, iss. 4, pp.281-289.

Venom Immunity

In my last post about the beautifully deadly blue ringed octopus I mentioned that even though they are toxic enough to kill 10 men they are immune to their own venom. This topic is of immunity has not been extensively explored and there is no clear answer to why this occurs in some species and not others. I was able to observe the effects of death adder (Acanthophis antarcticus) venom on another of the same species. The male was placed in the female’s enclosure for breeding when the female bit him on the head and envenomation occurred. There was local swelling at the bite site and subdued behaviour for two to three days. After this period the male returned to normal, eating and displaying active behaviours. He was reintroduced to the female and successfully mated. This same scenario has been observed with species such as red belly black snakes (Pseudenchis porphyriacus) and Copperheads (Austrelaps superbus) however the outcome of these incidents resulted in the death of the individual bitten.

The immunity between separate species has been a little more deeply explored. One animal that is famous for its ferocity and fearlessness is the honey badger (Mellivora capensis). This carnivorous mammal is found mainly in Africa where it preys on an array of venomous snakes. The most remarkable attribute about the honey badger is its immunity to snake venoms. This is not a unique trait, there are many ophiophagous (venomous snake eating) mammals which also show an immunity to not only snake venoms but also many arachnid venoms.

https://www.youtube.com/watch?v=wPKlryXwmXk

(15/4/2014-3:10pm)

There have been some evolutionary debates on this topic. One main question is why have all mammals developed and immunity to animal toxins in the case of accidental envenomation’s however it has been hypothesised that accidental envenomation leads to strong avoidance behaviours and only prolonged predation on venomous organisms leads to immunity. A debate that has arisen and is currently being examined is whether venomous species are in an arms race with their prey or their predators.

There has been a lot of focus on this topic due to the medical applications that surrounds venom resistance, however it seems that evolutionary biologist have only just scratched the surface to what may be influencing the evolutionary direction of nature’s deadliest venomous animals.

References:

Voss, R, Jansa, S 2012, "Snake-venom resistance as a mammalian tropic adaptation: lessons from didelphid marsupials",Biological Reviews, vol.87, pp. 822-837.