We’ve all heard stories of snakes, jellyfish, or scorpions with deadly poison. However, why are these animals so poisonous when these poisons seem to be of little use to them?
I was dreaming about walking in the beautiful Corcovado National Park in Costa Rica when I suddenly felt the guide’s arm hit my chest. “Stop!” – he exclaimed, pointing to something hiding in the sand: “Sea snakes”.
Watching the yellow-bellied sea serpent vigilantly, a little puzzle popped into my mind. “Sea snakes”, – I remembered young, “- is the most dangerous snake. You have to be very careful. “Although this proposition is a bit of an exaggeration, it is true that some sea snakes are extremely poisonous. Several species of land poisonous snakes are equally poisonous, for example a bite of the house snake taipan contains enough poison to kill 250,000 rats And it’s not just snakes that have this “power.” One drop of poison from the cone can kill up to 20 people. A sting from a canned jellyfish can cause cardiac arrest and death within minutes.
All this raises a question: why do these animals possess such powerful weapons that they can kill dozens of prey when they are only used in individual situations, again when they never deliberately hunt large prey like the human?
It reminded me of an oral story about a spider, where they had the most powerful poison known to humans, but did nothing because they had no way of transmitting the poison. While this is just gossip (many believe it, but MythBusters broke it), it’s not that it doesn’t make sense. The most potent toxins seem to make no sense in evolution.
Pelamis platura (Pelamis platura)
The reason why an animal possesses a poisonous weapon is very simple. Toxins are a means of manipulating prey without risking a fight. In addition, the use of poison is also an effective defense tactic.
However, the strange thing is the excessive level of toxins found in nature. Why is a snake capable of killing hundreds of thousands of rats with each bite? It becomes even more confusing when we think of the “price” of a weapon as poison. The venom often contains a mixture of protein-based toxins, with the ability to coordinate to destroy internal organs. One type of snake venom may contain an ingredient that prevents blood from clotting, and another has the ability to destroy vỡ mạch máu. Kết quả của sự phối hợp này thế nào thì chắc bạn đã có thể đoán được.
Protein synthesis consumes considerable energy, but this is not enough to stop the evolution and development of animals containing thousands of peptides and proteins, even when this consumption is quite large. to these poisonous animals.
To some extent, some poisonous animals calculate these losses. It is difficult to experiment directly, but it seems that some species of snakes know how to regulate their toxic secretions according to the size of their prey, in order to avoid wasting poison. Additionally, an experiment performed on cave snakes showed an 11% increase in metabolic activity after toxic secretion. This indicates a relationship between physical exertion and the production of the toxin.
A steppe rattlesnake (Crotalus viridis)
However, from the classical point of view of natural selection, it can be seen that such “expensive” (biologically) properties would be rejected unless absolutely necessary. The same has happened to some species: after returning to the main egg menu, marble sea snakes lost their ability to produce toxins.
However, there is the fact that there are many species of animals on Earth that contain expensive compounds of toxins in the fangs, barbs or thorns that appear much stronger than necessary. Why is that?
From a traditional perspective, the high levels of toxins resulting from evolution have compensated for the shortcomings of these animals in other ways. Any desert dweller can tell you this: when it comes to scorpions, they’re not the big and fierce ones, beware of the smaller ones, like insects. Deathstalker – the most dangerous species of scorpion in the world.
“The box jellyfish is also a good example,” said Yehu Moran, a researcher at the Jewish University of Jerusalem. Recently, he and his colleague Kartik Sunagar jointly produced a statistic of natural selections that work with toxins in poisonous animals. “They are very fragile and the fish with their muscles can cause the canned jellyfish to break from the inside while the jellyfish try to eat the fish,” he continued. Therefore, the poison must be 100% effective and cause rapid death. ”
In the wild, whether the predator is small, weak, or slow, it is essential that the poison has the ability to neutralize the prey almost immediately to prevent the prey from escaping or fighting. meet. In such cases, it is understandable that a high content of toxins is the optimal choice.
Poisonous canned jellyfish (Carukia barnesi) digests two fish
It doesn’t seem relevant, but there is an economic problem somewhere. The interior taipan snake lives in the arid desert of central Australia, and the reason why the poison causes immediate and certain death is easy to understand. In the desert, having to eat today for tomorrow, the snake does not have enough to allow a prey to escape.
But even so, the poison so powerful it could kill 250,000 rats in one bite still seemed a bit redundant. In response to this figure, Wolfgang Wuster, a snake poison expert at Bangor University, UK, has a fairly simple answer: “It’s because they don’t eat lab rats. Watching the lethal level of the toxin in rats has absolutely nothing to do with the behavior of snakes in the wild. “
PThe main method of assessing the toxicity of snake venom was a test called LD50 (lethal dose of 50% – the amount of poison needed to kill half the group of animals). Although it is widely used, it has its drawbacks. “The mouse model captures standard data,” said Robert Harrison, head of snake research at the Liverpool School of Tropical Medicine. But mammals are not always part of the host’s diet, so mammalian toxicity is simply a standardized measure unrelated to toxicity. amphibians, arthropods or birds. “
An indoor taipan snake (Oxyuranus microlepidotus)
Most poisonous animals have only a narrow specific range of prey, and it is these prey that shape their toxic growth. The consequence has been a co-evolving arms race. The prey develops resistance to the poison, only to be confronted with the more venom that emerges from the predator.
The astonishment at the number of rats that can be killed by a single snake bite is… as absurd as the surprise that a cheetah can easily outrun a turtle. Cheetahs simply did not evolve to hunt turtles, and conversely turtles did not evolve to escape the claws of the cheetah. As Mr. Wuster said, “Nothing is absolutely toxic. If you want to know how toxic something is, the first question I’m going to ask you is, “toxic enough to kill anything?”. “
Of course, testing the toxin on rats was not unreasonable. “This type of test is primarily designed to check mammalian toxicity – or we could say it – for the purpose of creating an antivenom,” Harrison explained. But not all mammals are overly sensitive to toxicity. Palm mangoes, ground squirrels, or even certain types of porcupines are able to survive bites from certain types of snakes – the bites can be life-threatening to humans.
The “super rat” Mr. Wuster mentioned may have developed an ability to resist snakebite because it is a key ingredient in the snake’s diet. Paradoxically, some animals are particularly vulnerable to certain types of poison simply because they are targeted by poisonous predators. For example, poisonous echis-scaly snakes feed primarily on scorpions and produce higher levels of scorpion-specific toxin. A similar syndrome is seen in coral snakes, where they can produce more venom for their preferred prey – fish, rodents or other snakes.
In such cases, it seems that the prey species do not have to undergo evolutionary pressure to survive under the action of a poison, since in their habitat poisonous snakes are not common. If they are faced with attacks from various predators, of which snakes are only a small fraction, then there is little pressure to evolve a specific defense with snakes – especially when it is a consuming process. energy.
The production of many different types of toxins has also been associated with the evolution of venom. The more ingredients are added to the venom, the more difficult it is for a prey to become immune to it. As can be seen, the most complex types of venom are favored by natural selection.
In published research, Sunagar and Moran found that this is exactly what happened to certain groups of animals – like snakes and cones, which became relatively toxic. here evolving. Some other poisonous animals, such as jellyfish, spiders or millipedes, with a longer evolutionary history, produce less poison. They seem to have passed a second evolutionary stage, where there is a “purification” of most of the components of the venom, and instead focuses on obtaining a small amount of the toxic ingredients. high calculation.
Cockles are poisonous and can be fatal
Fortunately, no poisonous animal evolved to drive us humans away, but even then thousands of deaths were recorded after exposure to snakes, jellyfish, scorpions and other poisonous organisms. “Primates do not seem inclined to develop resistance to poison,” Wuster explained. Therefore, it is more likely that an animal that has developed venom poisonous enough to take down a subject with high poison resistance will also be able to defeat a human.
There are also many cases that can also be considered due to … unlucky, maybe for example, the bite of the spider Atrax robustus will result in danger to human death, but it is almost harmless. with rodents. Since the spider did not evolve to hunt humans or rodents, this represents nothing more than an unfortunate match between the spider’s neurotoxin and a receptor in some of their cells. me.
Of course, studying the effect of venom on human physiology is very important. Such studies will allow us to develop antitoxic drugs, as well as a number of other drugs, such as captopril, a blood pressure drug, which are formulated from the poison of the snake. However, in order to truly understand toxins, we need to broaden the scope of research, not only with humans, but also to study how venoms are used in natural environments.
An Atrax robustus spider
What needs to be clarified is that poisons, like many other things useful in the animal kingdom, also come at a cost. Snakes, jellyfish or cockles do not develop extremely powerful poison just for this. Their venom is “specialized”, with the ability to do the right thing – although it is not always obvious to us.
Back in Costa Rica, our guide managed to use two sticks to put the sea serpent back in place, to avoid preventing passersby from stepping on it. I was happy to come out of a horrible death and keep walking.
Later, I learned that I didn’t need to be so worried. It turns out that our sea snake is not the highest ranked species on the poisonous animal list. Additionally, even though its venom was strong enough to kill a bitten person, due to its small jaw and fangs it rarely bites anything larger than a normal fish. And the snake is only interested, because naturally fish are part of their diet, and humans are not.