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Emily: Venoms and poisons, substances that oughta make us
check our shoes for spiders and look sideways at berries
we find in the forest.
The animals and plants that have evolved these unique properties both terrifying and
fascinate us.
No matter how fragile or harmless they may appear, a negative interaction with
a venomous or poisonous creature can range widely from minor
discomfort to death.
The terms venomous and poisonous are often used interchangeably
but they're two very different things.
To start out with both are toxins
substances created by living things that can do harm to other living things. If a toxin is actively
injected into you by a bite or a sting that organism is venomous. If you absorb the
toxin like by eating it, breathing it in or by rubbing it on your skin,
then that organism is poisonous.
Some animals produce substances that are both a venom and a poison.
For example when the spitting cobra sprays you in the eyes
the liquid gets into your body through your skin making it a poison.
But get too close and the cobra will bite you,
injecting that same liquid making it a venom.
Spitting cobras excluded, poisons are pretty passive.
The critter has to sit and wait to be touched or bitten because of
these poisons are generally used to defend against predators
Venom on the other hand is active so it can be used to ward off predators and to hunt prey.
So remember, venoms are injected and poisons are absorbed.
Today we're looking at a few species from a group of animals
well known for its venomous and poisonous
members, the reptiles and the amphibians.
To learn more about how they've evolved these toxins and how they're used.
Emily: Poisons!
Many toxic reptiles hold way more of their death juice than they really need
and it's because of the evolutionary arms race.
(Definitely not that kind of race).
Take the cane toad.
Behind its ear is a gland that produces a poison called Bufo toxin that kills by
interacting with the muscles of the heart making it beat so hard that it eventually stops.
It's fatal to almost any animal that tries to eat it but in its native range of Central and South
America, the cane toad does have natural enemies like the false water cobra.
Over many generations the false water cobra became resistant to the cane
toad's poison and in response the cane toads began producing even more poison,
causing the snake to develop more immunity with the snake currently winning the arms race.
Then back in
1935, on the other side to the planet in Australia,
sugarcane farmers were looking for a solution to a problem.
Sugar cane beetles and their larvae were destroying their sugarcane crops.
But wrongly assuming that the cane toad would be a more natural solution than using pesticides,
humans introduced the cane toads to Australia from Hawaii
hoping that they would eat the scarab beetles and turns out it didn't work.
Instead the cane toads became an incredibly destructive invasive species,
that is still expanding its range across Australia today.
The poisonous nature of the cane toads meant not only
are they killing off the animals that they eat, but also the animals
who are unaware of their poisonous nature and are trying to eat them.
Their introduction caused a massive die-off of many of Australia's
native predators including these adorable lizards
This is a shingle back skink or a bluey, as Australians like to call them, because of their signature blue tongues.
They're omnivorous and will eat almost anything they can fit in their mouths including king toads.
Unlike the false water cobras, blueys didn't evolve alongside
the cane toads and therefore haven't built up a natural immunity to their toxin.
But the lizards did have an unlikely ally in their arms race against
the toads in the form of a poisonous plant called mother of millions,
in an interesting case of cross kingdom convergent evolution,
these plants have evolved a very similar poison to the cane toads.
Before the toads got there
the blueys were eating mother of millions and getting poisoned.
Not all of them died in the ones who survived went on to breed
producing more poison resistant skinks.
So in the area where mother of millions grows the blueys are winning the race,
because they've had a head start on resistance.
But in other areas of Australia, where there are no plants to help them out,
deaths via cane toad poisoning has completely wiped out
populations of our blue tongue friends.
Emily: Venoms!
When it comes to toxin resistance and winning the evolutionary arms race if you compare to the king cobra,
king cobras are ophiophagus, meaning that their diet is almost
entirely made up of other snakes, many of which are venomous.
In addition to producing its own neurotoxin,
the king cobra also needs to be immune to the venom of the snakes that it eats.
So snakes like the common krait which kill up to 80% of the humans that it bites, can bite and attacking cobras
continuously with little effect.
These two snakes are in a two-way arms race,
the cobra must maintain a level of toxicity that can kill the krait
and also maintain its own immunity to the crates powerful venom.
All of this is very expensive for snakes, the energy cost of making more venom varies by the species
but it can be incredibly high.
For example, for a full three days after biting, one sixth of an
australian death adder's energy is put into making more venom.
That is a lot. Pregnant humans put 1/6 of their energy into growing a baby.
This is why many venomous snakes display visual cues
that advertise their toxic nature including warning coloration,
rattles and hoods.
This heads-up messaging communicates that they'd rather not waste their precious venom on something
they can't eat, like a human.
Snakes aren't only in an arms race with their prey and one another,
anthropologist, Dr. Lynne Isbell's research suggests
that humans are in an evolutionary arms race with venomous snakes too.
According to her work humans evolved better color vision and an eye for detail,
while snakes developed more potent venom and better camouflage to avoid detection.
Our bodies react to seeing a snake
before we consciously know that they're there.
Both poisonous and venomous animals terrify some people,
but they also provide us with life-saving medications made from molecules
that would otherwise be deadly.
The best-selling drug of all time is captopril, a heart failure in blood pressure
medication made from Brazilian pit viper venom.
Yew trees produce a poison that has been on the market as a cancer
medication since the 90s.
Aside from any potential
benefits that humans may gain from extracting
the toxins from these animals, they play an important role in their environment,
so let's respect and appreciate not only these toxic animals,
but also the species that are co-evolving alongside them, including ourselves
It still has brains on it