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Author Topic: QotW - 09.03.29 - Why are Australian snakes so toxic? (Elapids vs Vipers)  (Read 7484 times)

Offline DodgeyDamo

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I'd like to know 'Why are Australian snakes SO Toxic?"
 
If we assume that the LD50 tests on mice would have similar outcomes for humans, then what makes Australian Elapid snakes so toxic in comparison to Vipers/Colurbids?

Would it be fair to say that the toxins and venom delivery systems (fangs) of Vipers are more "efficient" that that of Elapids and therefor from a Evo-Bio-Geographical view, has the absence of Vipers from Australia (an effect of Wallace's line?) "saved" our lovely Elapids from being "outcompeted? The main problem with this, that I can see, is that Elapids and Vipers happily(?)coexist in Asia and Africa......

I also thought it may be due to climate...Australia has undergone major climate change since it separated from Gondwana, and has dried out considerably since....so I thought maybe Australian snakes evolved a kind of

'envenomate that prey item so much, it dies then and there, therefor Taipan doesn't have to spend energy looking for where its final resting place may be" which I thought may have had some kind of selection pressure for our Joe Blakes, but America and Africa have also undergone massive climate change over the past few million years....

Or is it that Australia extant/extinct Fauna take/took more venom to kill?

Thanks Guys
DodgeyDamo [O8)]
« Last Edit: 22/03/2009 21:57:30 by chris »


 

Offline Chemistry4me

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Offline DoctorBeaver

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As stated in that article, co-evolutionary factors may play a part. However, Australila is mostly desert and consequently prey is comparitively rare compared to other regions on Earth. The snake would need to ensure that if it bit the bite would kill.

Sidewinders that live in deserts also have highly effective venom.

It is not true in all cases, but I think it may be 1 of the factors involved.
 

Offline Chemistry4me

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It's just as well that they can't swim across the ditch!
 

Offline DoctorBeaver

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But they could hitch a lift with a boatload of illegal immigrant Bruces.
 

Offline Chemistry4me

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Nah, they'll all be dead by the time they've arrived. [xx(]
 

Offline DoctorBeaver

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They'd probably get lost & arrive at Norfolk Island.
 

Offline Madidus_Scientia

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And maybe by concentrating the venom more, they waste less water
 

Offline DodgeyDamo

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Chemistry4me thanks for the link...but I didn't agree with much of what was posted there...

Doctor Beaver and Madidus_Scientia thanks for your replies.

Madidus_Scientia >> The water/cost is a point I hadn't thought about...interesting....but many(?) vipers also live in desert regions...with "less concentrated(?)" venom. And also some Elapids not only produce a more toxic venom but they also produce more of it when envenoming their prey....so any water saved by concentrating the venom would be lost by over production....     

Doctor Beaver >> prey is comparatively rare in Australia's desert...but up to 50 species of small terrestrial (bite sized) mammals went extinct from these areas due to the introduction of Cats/Foxes/Rabbits and the eradication of Dingoes and Aboriginal people. Rabbits obviously not a direct threat to mammals but huge numbers provided prey base for foxes which ate everything as they spread through the continent....Dingoes and Australian Aboriginal peoples killed and ate cats thus keeping their numbers to a minimum...untill they themselves were killed by white pastoralists... and also it has only been in the last million years or so that Australia has had any deserts...historically its pretty much always been hotter and wetter....Wouldn't this equate to more prey availability thus negating selection for higher venom toxicity?

But on the other hand, most Australian snakes diets contain a relatively high proportion of skinks and amphibians.....both abundant in arid Australia (Yes we have desert frogs...)  so the absence of presence/absence of mammals shouldn't matter too much anyway.....!

I think Current distributions of prey density in Australia are very skewed away from what what would have been the norm for much of the time elapidae was evolving in Australia...so I don't think that lower prey density could have been a driving force for the evolution of such a high proportion of highly toxic serpentines in Australia... 

Does anyone know of any studies into the efficiency/costs of elapidae vs viperdae venom?

 [O8)]
 

Offline DoctorBeaver

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Quote
...but up to 50 species of small terrestrial (bite sized) mammals went extinct from these areas due to the introduction of Cats/Foxes/Rabbits and the eradication of Dingoes and Aboriginal people. Rabbits obviously not a direct threat to mammals but huge numbers provided prey base for foxes which ate everything as they spread through the continent....Dingoes and Australian Aboriginal peoples killed and ate cats thus keeping their numbers to a minimum...untill they themselves were killed by white pastoralists... and also it has only been in the last million years or so that Australia has had any deserts...historically its pretty much always been hotter and wetter

Facts of which I was unaware. Thank you for enlightening me.
 

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