Octopus’ ‘planned suicide’ after mating finally explained

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The octopus, this cephalopod with extraordinary powers, is one of the most intelligent creatures in the animal kingdom. However, a very odd self-destruct behavior allows him (with a few exceptions) only a short longevity, and his suicide appears to be very precisely programmed after mating. A change in cholesterol metabolism caused by the cephalopod’s optic gland must have been responsible for this tragic event, according to a new study. This gland, in particular, would undergo massive changes in a female octopus after a successful mating, producing steroid hormones that cause her to commit suicide. According to researchers, a similar hormonal change in mammals (including humans) can cause the same suicidal behavior as in octopuses.

Soft-bodied cephalopods such as octopuses have the largest and most complex central nervous system, as well as the largest brain-to-body mass ratio of any invertebrate. In particular, this gives the octopus the impressive abilities that have always fascinated scientists. For example, it can change color to blend in perfectly with its surroundings, or mimic the shape of a venomous animal to fool predators. He can even wield tools and solve complex cognitive puzzles.

He is also able to regenerate his severed limbs, those powerful tentacles that he skillfully wields to make him a superior predator, in addition to his hunting arsenal (venom, suckers, beak, etc.). Then one would think that little could surpass this exceptional animal, but oddly enough, its average lifespan is very short. While some primates and corvids live for decades, shallow-water octopuses such as the California two-spotted octopus (Octopus bimaculoides), live an average of only one year.

Like many other cephalopods, the octopus only reproduces once in its life, after which its life cycle ends. After laying her eggs, the female octopus, in particular, begins a process of self-destruction as she begins to starve and self-mutilate, retaining just enough strength to incubate her eggs to hatch before succumbing to her poor health condition.

According to a new study published in the journal Current biology, captive-bred females even seem to deliberately speed up the process by mutilating themselves and frantically twisting their tentacles. ” What is amazing is that they go through this progression of change where they seem to go insane right before they die. “Clifton Ragsdale, professor of neuroscience at the University of Chicago and one of the authors of the study, said in a press release. Moreover, this “programmed suicide” will also be observed in males, who, after reaching the age of about a year or a year and a half, will also stop feeding and eventually die shortly after their females.

The new study, led by the University of Washington and Illinois, builds on earlier research that demonstrated the role of the octopus’s optic gland in reproduction and longevity. This gland, in particular, is its main neuroendocrine center, the functional equivalent of which in vertebrates is the pituitary (or pituitary). In female octopuses, it was first found that after mating, the glands change in such a way that cholesterol metabolism changes, leading to dramatic changes in the steroid hormones produced. Which could explain his suicidal behavior.

Three biochemical pathways involved

In 1977, Brandeis University psychologist Jerome Wodinsky demonstrated that after the removal of the optic glands, Caribbean two-spotted octopuses become mothers (Briarean octopus) dropped their eggs and began to feed again. They then lived several months longer than those who still had glands. Already at that time, scientists understood that the gland probably secreted “self-destructive” hormones, but the metabolic mechanisms that cause this phenomenon were not yet fully understood.

To reach their conclusions, the researchers in the new study sequenced the activated and deactivated genes in the cells of the optic glands of female octopuses.Octopus bimaculoides), at different stages of their decline. Then they noticed that when the cephalopods began to starve, the level of activity of genes that metabolize cholesterol and produce steroids increased.

Cholesterol is indeed involved in many vital physiological processes in animals, such as cell membrane flexibility and the production of stress hormones.” but it was a big surprise to see that it also plays a role in this life cycle process. says (referring to the self-destruction of the octopus) Z. Yang Wang, assistant professor of psychology and biology at the University of Washington and lead author of the study.

The research team also found three different biochemical pathways associated with increased levels of steroid hormones after reproduction. The former produces pregnenolone and progesterone, two steroids commonly associated with pregnancy. Another produces maternal cholestanoids or intermediates for the formation of bile acids, and the third leads to an increase in the level of 7-dehydrocholesterol (or 7-DHC), a cholesterol precursor.

Some of these pathways are also activated to produce cholesterol in mice and other mammals. For humans, high levels of 7-DHC are toxic. In particular, this phenomenon is observed in Smith-Lemli-Opitz syndrome (a genetic disease caused by a mutation in the enzyme that converts 7-DHC to cholesterol). Children with this disease suffer from severe developmental and behavioral problems, often self-harm. According to the research team, this behavior is very similar to what is seen in octopuses.

Source: Current Biology.

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