“Their life is not that complicated,” explains the neuroscientist. “So maybe they survive just long enough to do what they have to do. »
And even if they developed these pathologies, no one knew about it. “There is no behavioral scale for muskox. We cannot therefore say whether they are losing their memory a little or not, ”she adds.
Ackermans now wants to study different species of woodpeckers to see if the headbutts they give cause them brain trauma. The only other study to look at the brains of birds found traces of tau protein, but “not really in any specific logic,” she says.
COUPLE UNTIL DEATH
To some likely, the muskox represents an interesting parallel to certain marsupials, says Diana Fisher, a mammalian ecologist at the School of Biological Sciences at the University of Queensland, Australia.
Small and carnivorous, antechinus are a genus of marsupials native to mainland Australia and Tasmania. In recent years, they have made headlines for the way males practice semelparity, that is, one big reproductive cycle followed by an expected death. Females can live two to three years or more, but males rarely last longer than eleven months.
“They have a very frenetic mating season,” Fisher says. Matings can last for twelve to fourteen hours, and thereafter the male tries to mate with as many other females as possible, leading to his death.
“The collagen in their skin is breaking down, their intestines are breaking down, and they are bleeding internally,” says Fisher. “They become very susceptible to parasites and diseases, and their immune system breaks down. In a matter of weeks they will be dead.
“All of this is rather unusual for mammals,” says Fisher, because mammals tend to survive long enough to experience multiple mating seasons.
Suicidal breeding is more common in insects, fish, plants and arachnids: when another species native to Australia, the red-backed black widow, mates, the male places himself in its mouth after the act.
“This discourages the female from continuing to mate, as she is busy eating,” adds Fisher.
In large colonies of social insects, a similar but slightly different dynamic occurs.
When a European bee stings a soft-skinned aggressor, such as a bear, it dies when its stinger becomes lodged in the victim’s skin. An explosive ant may tear its abdomen in two to defend its nest against attackers. And in some species of termites, the older ones can turn into suicide bombers.
But what explains such a willingness to kill oneself, from the point of view of evolution?
“It’s quite simple,” replies Thomas Seeley, a biologist at Cornell University and author of The life of bees, in an email. “Workers complete genetic (evolutionary) success not by reproducing themselves, but by helping their mother, the queen of the colony, to do so. This aid can notably aim to defend the colony,” he explains.
“Some researchers call it a ‘superorganism,'” says Alice Laciny, an entomologist who works on explosive ants at the Museum of Natural History in Vienna, via email. “Thus, a colony of ants or a hive of bees is more like a single large animal, of which the queen represents the reproductive organs. Workers are numerous and only need small amounts of resources to grow, so they are similar to cells in a body, in a way. »
As with muskoxen, what strikes us as violent, self-destructive behavior on the part of worker ants seems worthwhile, as long as it leads to reproduction.
“In this system, it is by protecting its queen and its sisters, going so far as to sacrifice itself if necessary, that a worker ant can protect and transmit its genes”, explains Laciny.
THE ULTIMATE MATERNAL SACRIFICE
The distance some mothers are willing to go to give their young a chance represents another form of sacrifice found in the animal kingdom.
After birth, some species of amphibians, legless, literally eat the top layer of their mother’s skin as their first meal. African social spiders Stegodyphus dumicola go even further: some females allow their young to practice matriphagy, that is, she lets them kill and eat her.
Giant Pacific octopuses are perhaps the most self-sacrificing mothers. Females can watch over their eggs for an impressive four years during which they don’t even eat.
“Inevitably, females exhaust all their body reserves and die while guarding their eggs,” says Fisher.
“It takes pain for them, but that’s how many species achieve the greatest success in ensuring the survival of the next generation. »