Animals that defy death with their ability to ingest poison from other species

First there were the microbes, which used chemicals to eliminate their competitors or attack host cells they had invaded; Then animals to hunt prey or scare away predators; And plants to defend themselves against herbivores.

Many animals responded by developing mechanisms to survive with these toxins. Sometimes they store it to use against their opponents.

Scientists are beginning to uncover these ingenious anti-venom defenses, and from this research they hope to identify better treatments for poisoning in humans.

More importantly, they are discovering a force that has quietly helped shape biological societies, says evolutionary biologist Rebecca Tarvin of the University of California, Berkeley, who oversaw the snake experiment and wrote about these strategies in the 2023 issue of the journal. Annual review of ecology, evolution, and systematics.

“Just a milligram of one compound can change all the interactions in an ecosystem,” Tarvin explains.

Species become toxic in different ways.

Some produce their own toxins.

For example, bufonid frogs produce molecules called cardiac glycosides that prevent a protein called the sodium-potassium pump from moving ions in and out of cells.

This transport is essential for maintaining cell volume, muscle contraction, and transmission of nerve impulses.

Other animals have toxin-producing bacteria in their bodies. This is the case of puffer fish, whose flesh, which contains tetrodotoxin, can be fatal if consumed.

Many others get their toxins through food. This is what happens with poison dart frogs, which devour insects and mites that contain toxins. Among these frogs is the type that was used to feed ground snakes.

As some animals evolved to become venomous, they also modified their bodies to avoid poisoning. The same thing happens with the creatures you eat or those you feed on.

The best-studied adaptations involve changes to proteins that are normally inactivated by toxins, such that they become resistant.

For example, insects that grow and feed on glycoside-rich milkweed plants have evolved sodium and potassium pumps to which the glycoside cannot bind.

But modifying a biomolecule can cause complications for the organism, says molecular biologist Susanne Doppler of the University of Hamburg in Germany.

In his studies of the milkweed insect, which feeds on milkweed seeds, he discovered that the more resistant the sodium and potassium pump was to glycosides, the less efficient it was.

This presents a problem in neurons, where the pump is particularly critical.

Bedbugs seem to have evolved a way around this problem. In a 2023 study, Doppler and his colleagues analyzed toxin resistance in three versions of the bomb produced by this organism.

They discovered that the most functional part of the brain is also the most sensitive to toxins. Doppler explains that the milkweed must have evolved other ways to protect the brain from glycosides.

The scientist suspects that proteins called ABCB transporters are found in cell membranes and remove waste and other unwanted products from cells.

Doppler discovered that some sphinx moths use ABCB transport proteins, found around their nervous tissue, to move cardiac glycosides out of cells. Maybe milkweed does something similar.

The researcher is also testing the hypothesis that many insects have ABCB transporters in their gut membranes, which prevent the body from absorbing toxic substances.

This could explain how the red lily beetle, which feeds on glycoside-rich lily of the valley, appears unaffected by the toxins and simply excretes them. Doppler reported in a 2023 study that the resulting feces have the advantage of repelling predatory ants.

For true wild snakes, the liver seems to be the key. Through cell culture experiments, Tarvin’s team obtained evidence that some components of this snake’s liver extract protect against toxins from three-striped poison frogs.

The team hypothesizes that snakes possess enzymes that convert deadly substances into non-toxic forms, similar to the way the human body converts alcohol and nicotine.

The snake’s liver may also contain proteins that bind to toxins and prevent them from binding to their targets, absorbing them like a sponge.

Scientists have discovered proteins with a ‘poison sponge’-like function in the blood of some poison frogs, allowing these amphibians to resist deadly toxins, including saxitoxin and alkaloids.

Ground squirrels in California appear to use a similar strategy to defend themselves against rattlesnake venom, a mixture of dozens of toxins that destroy blood vessel walls and prevent blood from clotting, among other effects.

Ground squirrel blood contains proteins that block some of these toxins, acting similarly to the proteins that rattlesnakes themselves use to protect themselves in case venom escapes from their specialized venom glands.

The venom cocktail varies between snake populations, and evolutionary biologist Matthew Holding of the University of Michigan has evidence that the ground squirrel’s antivenom is adapted to local snakes.

But these defenses are not infallible. Rattlesnakes are constantly developing new venoms to counter the squirrels’ adaptations, Holding says, and even a rattlesnake can die if injected with enough of its own venom.

This is why animals, even resistant ones, try to avoid toxins as a first defense measure. Hence the behavior of terrestrial snakes of dragging prey and the habit of some turtles to eat only the ventral skin and entrails of poisonous salamanders, and not the dorsal skin, which is fatal.

Even insects such as monarch caterpillars, which are resistant to cardiac glycosides, cut the veins of milkweed plants to drain the toxic fluid before feeding on the plant.

Many animals also find ways to safely store the toxic chemicals they consume for their own purposes.

For example, the iris dogbane beetle obtains cardiac glycosides from its host plants and then, perhaps using ABCB transporters, transfers them to its back for defense.

“When these beetles are disturbed, you can see little droplets on their dorsal surface,” Doppler explains.

Through this type of toxin exploitation, some insects become dependent on their host plants for survival.

The relationship between the monarch butterfly and the milkweed plant is a typical example, and also a clear example of the wide scope these associations can have.

In a 2021 study, evolutionary biologist and geneticist Noah Whitman of the University of California, Berkeley, and one of his colleagues identified four animals that had evolved to tolerate cardiac glycosides, allowing them to feed on monarch butterflies.

One is the black-headed grouse, a bird that feeds on monarch butterflies in the spruce forests of Mexico’s mountains, where the butterflies fly to spend the winter.

Think about it, Whiteman says: The poison made in milkweed plants in Ontario’s prairies helped shape the bird’s biology, so that it could safely forage for food in a forest thousands of kilometers away.

“The journey of this small molecule and its impact on evolution is simply amazing.”

You can view the original note in English and links to scientific studies in it BBC Futureland.

This article was originally published on known It is reproduced here under a Creative Commons license.

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