Not many people are very fond of spiders, they are
usually seen as horrid vermin and always an uninvited guest in thousands of
homes around Australia. However spider are very effective, deadly predators.
They are the pioneers of trapping and ambushing prey which in some cases can be
ten time the size and weight of the spider. Arachnids have been around for the
last 300 million years. They come in all shames and sizes from species the size
of a pin head to the goliath bird eater (Theraphosa blondi) growing up to 30cm across. Australia has its fair share of
spiders with over 2,500 species but there is one in particular which is most notorious
throughout the country; the Sydney funnel web (Atrax robustus).
M Gray © Australian Museum
Atrax robustus
M Gray © Australian Museum
Photo by M.Gray at the Australian Museum
M Gray © Australian Museum
This extremely
dangerous spider is considered one of the most toxic in the arachnid kingdom
and has resulted in 14 human fatalities prior to the production of anti-venom
in 1981. There are two lethal neurotoxins which have been isolated from the
venom of this spider they are a robustoxin and the versutoxin. The effects from
a bite can become very server in a short amount of time (Szeto et.al 2000).
Photo by Sam Rutty
Generally people come into contact with male spiders
as they travel across the landscape in search of a female. It is the male which
carries the most toxic venom possibly due to a defensive evolutionary responses
as the male are vulnerable to other predators during this time. Females do not
leave their burrows and therefor face less chance of predation. Female bites
are still extremely painful and can lead to some unpleasant effects but are not
fatal. This is due to the lower levels robustoxin in the female’s venom (Graham
et.al 1997). Robustoxin effects the neuromuscular junction, immediately disturbing respiration, blood pressure and causing server hypotension (Mylecharane et.al 1989).
Male (left) and Memale (right)
Photograph courtesy of Australian Venom Research Unit
Whatever your view of these beautiful spiders, it is
impossible to deny the chemical wonders that reside in their little exoskeletons.
The potential pharmaceutical benefits of their venom is still being explored however
research continues in the hope that in the near future we will harness the
power of venom.
References:
Mylecharane, E. J., Spence, I., Sheumack, D. D.,
Claassens, R., & Howden, M. E. (1989). Actions of robustoxin, a neurotoxic
polypeptide from the venom of the male funnel-web spider (Atrax robustus), in
anaesthetized monkeys. Toxicon, 27(4), 481-492.
Nicholson, G. M., Walsh, R., Little, M. J., &
Tyler, M. I. (1998). Characterisation of the effects of robustoxin, the lethal
neurotoxin from the Sydney funnel-web spider Atrax robustus, on sodium channel
activation and inactivation. Pflügers Archiv, 436(1), 117-126.
Szeto, T. H., Wang, X. H., Smith, R., Connor, M.,
Christie, M. J., Nicholson, G. M., & King, G. F. (2000). Isolation of a
funnel-web spider polypeptide with homology to mamba intestinal toxin 1 and the
embryonic head inducer Dickkopf-1. Toxicon, 38(3), 429-442.
An interesting post (and reference to a terribly filmed, but funny film)! I find it intriguing that female funnel webs are less toxic. While the males are subject to higher predation pressure, why are they incredibly toxic (when compared to other spiders)? Is their venom toxic to other individuals (i.e. will funnel webs die if bitten by other funnel webs)? You mentioned the function of robustoxin, but what about the effects of versutoxin? Cool post!
ReplyDeleteHaha it was a dodgy movie. According to a few accounts funnel webs are very aggressive feeders which will very often take larger vertebrates. This is more likely the reason they are so toxic. Female eating males after mating it has not been frequently recorded in this species. I had some trouble finding any literature on their immunity to their own venom. The lack of evidence is probably correlated with the lack of cannibalistic behaviours. The versutoxin is another neurotoxin which is found in a wide range of spider venoms, it is less potent than the robustoxin. I have looked at some other papers and from what I can see only Atrax robustus venom contains the robustoxin and other Antrax species contain the versutoxin.
DeleteIt's interesting that male funnel webs are so much more toxic than females. I know in some cases female spiders kill the males. Do you know if this is the case for funnel webs, and if it is, could the more toxic venom protect the males from their mates?
ReplyDelete