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.

Put a Ring On It

The blue ringed octopus (Octopus maculosa) is one of the most striking species in the ocean and quite possibly one of the most venomous organisms on the planet. O.maculosa only grow up to  20cm from tentacle to tentacle and weigh a mere 100g however these tiny molluscs are considered one of the most venomous creatures on earth.  

  Their diets mainly consist of small crustaceans such as crabs and shrimps which they kill using their venom and strong beak to open tough shells. There are two ways in which the octopus can deliver venom to its victim. The first is by releasing a cloud of toxin on to the animal which is then absorbed though the gills, within seconds the animal becomes paralysed and is then safe to consume. The other tactic is to grab onto the animal and inject the venom though the beak directly into the victim.

Octopus maculosa

(http://www.oceanwideimages.com/categories.asp?cID=66)

(311/14 -18.15)

  The venom produced by this octopus is known as a Maculotoxin (MXT). It is a cocktail of neurotoxins which effects the brain blocking signals to voluntary muscle systems causing the diaphragm to shut down and breathing to cease. Complete paralysis can occur within minutes with death soon to follow if untreated. The impressive aspect of this venom is that it is extremely stable at a molecular level, retaining its toxicity at 50oC in a hydrochloric acid solution. A single octopus weighing 25g contains enough toxin to paralyse ten humans weighing 75kg each. Even with this toxicity, O.maculosa are completely immune to their own venom.

  This is a very powerful punch for such a small creature. Its sinister beauty exposes it to every animal in the ecosystem which is unlike other octopus species which have evolved incredible mimicry techniques to evade predators. If threatened O.maculosa with flash its blue rings not only does the venom serve as a powerful as effective prey capture technique but also a strong deterrent to attackers.

Octopus maculosa

(http://www.oceanwideimages.com/categories.asp?cID=66)

(311/14 -18.1)

References:

M, S, Bonnet 1999, "The toxicology of Octopus maculosa: the blue ringed octopus", British Homeopathic Journal, vol.88, pp.166-171.

Not Quite So Cuddly

This post will move away from the obvious venomous animals such as reptiles, arachnids and various sea life and on to the furry little creatures that are considered cute and cuddly.The literature surrounding venomous mammals is an active battlefield so I will try my best not to ruffle any feathers or fur. The definition used to describe a venomous animal is a secretion produced by an animal in a specialised gland and delivered to the target thought infliction of a wound. The secretion must contain a molecule which disrupts the victims physiological process Fry et al (2009). The few mammals described as venomous where done so using the following definition.

  There are currently only 4 orders of mammals considered to be venomous they are the Insetivora (Shrews and Solendons), Monotremata (Platypus), Chiroptera (Vampire bats) and arguably Primates which are the pygmy and slow lorises. Lorises are a spanner in the works of toxicology labelling as they lack any delivery apparatus. The toxin is produced in a gland located on the elbow, licked and spread onto the teeth. Due to this lorises are considered as indirectly venomous.

Slow loris (Nycticebus coucang)

http://www.bbc.co.uk/nature/life/Slow_loris 

1.35pm 21/03/14

  The concept of a venomous mammal has been around since the mid 1900s however any symptoms following a bite ware discarded as a bacterial infection.It was not until 1992 that the idea was taken seriously after extensive research. It was also proposed by Dufton (1992) that although venom is a rare feature in extant mammals it would be widespread in more primitive species. There was very little fossil evidence to support this until 2005 when a fossil shrew dating back 6 million years was found to have distinct grooves the canine teeth which was an indication of a venom delivery system. Since then there has been multiple discoveries of insectivore fossils found to have grooved teeth and other mammals with crural spurs similar to the platypus. This evidence strongly supported the hypothesis that venom in early primitive mammals was widespread.

   The evolutionary history of the venomous mammals is still unclear and has only recently been investigated. Interestingly  Solendons produce their venom in the submaxillary gland which are also found in the Gila monster and Mexican beaded Lizard. The effects of the venoms are also similar but are made up of two different protein structures. This is an excellent example of convergent evolution at a molecular level between reptile and mammal venom and delivery systems.

References

Braun, R, Veril, H, Carlini, C 2012, Venomous mammals: a review, Toxicon, vol. 59, iss. 7-8, pp.680-695.

Fry, B, Roelants, K, Champagne, D, Scheib, H, Tyndall, J, King, G, Nevalainen, T, Norman, J, Lewis, R, Norton, R, Renjifo, C, Vega, R 2009, The toxicogenomic multiverse: convergent recruitment of protiens into animal venoms, Annual Reviews, vol.10, pp.483-511.

Venomous Lizard Kings

There has long been a debate on the  Komodo dragon (Varanus komodoensis) currently the largest living monitor lizard and its methods of bringing down large prey such as wild boar and even buffalo. It has been wildly excepted for many years that the nasty bacteria lurking the the jaws of the Komodo has been the secret to its hunting success.
   Komodo Dragons hunting has been widely documented in the wild and has shown that prey which has endured the gruesome bite from the giant lizard usually die from rapid shock and extreme blood loss. There is a very long painful death process for the prey species which may take up to several hours or even over a day for larger animals The deep wounds of a large animal may also become infected during this time. It would seem a logical thought that the source of the infection came from the mouth of the Komodo Dragon due it their lack of dental hygiene and constant drooling. However it seems this theory lacks vital evidence and does not factor in all of the surrounding variables.
  As i mentioned in my last post there is evidence to suggest the complex venom systems found in snakes originated from ancient lizards such as Iguanas and Varanids. Looking back over evolutionary history of V.komodoensis, is it possible that this species is using venom as a technique to bring down large prey? Fossil evidence suggest that these large monitors are the descendants of something even larger. Megalania (Varanus prisca) is the largest monitor in the fossil record and it lived right here in Australia. Close examination of the teeth of V.prisca shows a groove which runs from the base of the tooth to the tip.This groove indicates a primitive venom delivery system commonly seen in other lizard species. From this evidence it is entirely possible that V.komodoensis has inherited the venomous bite from Megalania. This groove however is not present in the  komodoensis tooth which may why this theory has been overlooked in the past.

Image from B.G.Fry et al. 2009 Comparing the V.komodoensis tooth to that of V.prisca.

A central role for venom in predation by Varanus komodoensis (Komodo Dragon) and the extinct giant Varanus (Megalania) 

A central role for venom in predation by Varanus komodoensis (Komodo Dragon) and the extinct giant Varanus (Megalania) 

  There is evidence to suggest that the amount of blood loss which follows a bite is not only because of the deep lacerations but also due to an anticoagulant property found in the venom of not just the Komodo dragon but most Varanidae species. This venom was extracted from the glands found in the bottom jaw which also compelling evidence that there is a much more sophisticated mechanism at work.
  This evidence answers my question from my last post. It seems that lizards have indeed evolved complex venom systems not only for defence but also for prey capture. with these recent discoveries there is no doubt that more reptilian species will be put under the microscope and there ancient secrets revealed.

   Photograph by Theo Allofs/Corbis

http://www.theguardian.com/world/2009/mar/24/man-mauled-death-komodo-dragon

11.15am  18/03/13

Ref:
B.G.Fry et al 2009 "A central role for venom in predation for Varanus komodoensis (komodo dragon) and the extinct giant Varanus (megalania) priscus", PNAS, vol.106, pp.8969-8974.
   
 

Origins of venomous snakes

Interesting paper which talks about the evolutionary path of snakes. Firstly thought to be closely related to Varanus species due to similarities in teeth and tongue structure. Surprisingly it is lizards like the iguanas which are the ancient ancestors to the venomous snake species of today. The evidence for this hypothesis is the presence of libial glads located in the upper and lower jaw at the base of the teeth. If these ancient lizards did indeed evolve the very first primitive venoms and apparatus for venom delivery then why did it not develop in modern lizard species?. There are only a handful of lizard species considered venomous but none of which are as advanced as the venomous snake species found today.

Kochva E, 1986, The origin of snakes and evolution of the venom apparatus, Toxicon, vol.25, no.1, pp.65-106.