Why do some animals sacrifice themselves in the course of evolution | National Geographic

A male musk ox can weigh about 400 kilograms and reach a speed of about 50 kilometers per hour during an attack. In the mating season, these furry giants from the Arctic Circle turn to each other, trying to strike their opponents with their large, sharp horns.

Over the course of their lifespan of ten to twelve years, male musk oxen suffer as many as 2,100 of these clogs.

You wonder how these animals survive without their brains being bombarded.

“People have long assumed that animals that had their heads blown off, such as musk oxen and bighorn sheep, somehow couldn’t get a head injury,” says neuroscientist Nicole Ackermans of Icahn College of Medicine in Mount Sinai, New York. “It’s like they have magic horns or something.”

But when Ackermans checked the scientific literature, she found that no one had investigated whether these North American herbivores had suffered brain damage from head strikes. So she and her colleagues decided to search for the brains of musk ox and bighorn sheep, obtained through expeditions, gifts from professional hunters, and herds kept in captivity for research.

“We discovered a specific pattern in all of our laboratory animals that is very similar to primary brain trauma in humans,” says Ackermans, lead author of an article about the research findings that appeared recently in the journal. Acta Neuropathology.

The new research could contribute to our understanding of brain injury in humans, Ackermann said, because bovine animals (animals such as bulls and sheep) have folded, twisted brains more similar to humans than, say, mice, which have smooth brains. .

It’s also evidence that species can engage in surprisingly self-destructive behavior over the course of evolution. To be sure, musk oxen are not alone in this regard.

“As long as it doesn’t kill you”

In their research, Ackermans and colleagues applied biomarkers to the brains of three musk oxen and four bighorn sheep. These chemical compounds reveal patterns of traumatic brain injury often associated with conditions such as Alzheimer’s disease or CTE (chronic traumatic encephalopathy) in humans. In this case, the scientists were specifically looking for what is known as the tau protein.

“When neurons are damaged, for example due to age, genetic problems, or mechanical collisions, they rupture and the protein is damaged and begins to form clumps,” Ackermans explains. “When you find a certain pattern, you can tell if the brain is normal or old, or if there’s Alzheimer’s disease or maybe trauma.”

Unfortunately, the biomarker method did not work well in sheep’s brains, although there were signs of a buildup of tau protein there. But the musk-drunk brains looked like a Christmas tree with all that tau glow.

At first glance, it may seem strange that normal behavior such as throwing tampons can cause so much damage. Ackermans says you have to see him in the long run.

“The musk ox gives and gets a lot of heads each year, but if it breeds successfully once, that’s actually enough,” she says. “As long as it doesn’t kill you, that’s all that matters from an evolutionary point of view.”

She believes that male musk ox probably live less than 15 years, while females can live from 15 to 23 years. Although the amount of tau protein builds up during a male’s life, it will likely never reach the level where it can lead to conditions such as Alzheimer’s disease or other forms of dementia.

“Their lives are not that complicated,” Ackermans says. “So they may go on long enough to do what they need to do.”

And even if they did get sick, who would notice? There is no measure of musk ox behavior. So maybe they forget a little.

Ackermann now also wants to study different types of woodpeckers, to see if they have brain damage from knocking their heads. The only other study of bird brains found some evidence of tau protein, but “it wasn’t in a certain pattern,” she says.

Die until you fall

Mammal ecologist Diana Fisher of the University of Queensland’s School of Biological Sciences explains that musk oxen are similar to a certain type of marsupial.

Broad-footed opossums are small carnivores found in inland Australia and Tasmania. They’ve been in the news in recent years because males have near perfect parity: they only reproduce once in their lifetime, and then die. Female broad-footed opossums can live for two to three years, sometimes longer. Males rarely live beyond eleven months.

“Their mating season is very intense,” Fisher said. Mating can last from twelve to fourteen hours and the males try to mate with as many females as possible – eventually their downfall.

“The collagen in their skin breaks down, their intestines are damaged, and they bleed internally,” Fisher says. “They become more susceptible to parasites and diseases and their immune system stops working.” They died a few weeks later.

“This is very special for mammals,” Fisher says. They usually live long enough to experience several mating seasons.

Suicide reproduction is more common in insects, fish, plants, and spiders. For example, another domestic male animal from Australia, the red-back spider, gets into the mouth of the female during mating.

“This prevents her from mating with another male because she is too busy eating,” Fisher says.

self-destructing insects

Similar mechanisms occur in colonies of large social insects.

If a European honey bee stings a soft-skinned attacker, like a bear, the insect dies because its sting remains in the victim’s skin. The bomb ant can rip its abdomen in half while defending its nest from attackers. And in some species of termites, older worker termites can transform themselves into suicide bombers.

But what is the evolutionary use of killing yourself?

Biologist Thomas Seely of Cornell University and author of Simple bee life, in an email. “Workers achieve their genetic (evolutionary) success not by giving birth to themselves, but by enabling their mother, the queen of the colony, to do so.”

“One of the ways they can help is to defend the colony,” he explains.

“Some scientists call this a ‘super being.’ In addition, an ant colony or bee colony is a type of large animal, and the queen is the reproductive organ,” entomologist Alice Lasini, who researches thrush ants at the Naturhistorisches Museum in Vienna says by email. There are countless subordinate workers who only need a little food, so they are like body cells.

As with the musk ox, the behavior we think of as aggressive and self-destructive for worker ants seems to be worth it, as long as it ultimately leads to reproduction.

“In this system, defending the queen and her sisters, if necessary by self-immolation, is the worker ant’s way of protecting and transmitting her genes,” Lacini said.

A mother’s highest sacrifice

Another form of sacrifice in the animal kingdom is what some mothers would do to get their young off to a good start in life.

Certain species of legless amphibians, amphibians, literally eat the top layer of their mother’s skin as their first meal after birth. Certain species of African social spiders take this one step further. They have matrophagia, the young that kill and eat their mother.

The giant squat can be said to be the ultimate self-sacrificing mother. Females sometimes monitor their eggs for up to four years without eating during that time.

“The females irreversibly deplete their reserves, causing them to die while guarding their eggs,” Fisher said.

“This is very sad for them, but in many species this is the most successful for their offspring in the next generation.”

This article was originally published in English at nationalgeographic.com

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