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Octopus, this cephalopod with extraordinary abilities, is one of the most intelligent creatures in the animal kingdom. However, his very peculiar self-destructive behavior only allows him (with a few exceptions) a short lifespan, and his suicide appears to be precisely programmed after mating. According to the discovery resulting from a new study, the change in cholesterol metabolism, caused by the optic gland of the cephalopod, will be the origin of this tragic phenomenon. This gland in particular will undergo a massive change in the female octopus after successful mating, by producing steroid hormones that induce the octopus to commit suicide. According to the researchers, a similar hormonal change in mammals (including humans) can lead to the same suicidal behavior as in an octopus.
Soft cephalopods such as the octopus have the largest and most complex central nervous systems, as well as the largest brain-to-body mass ratios, of all invertebrates. This gives the octopus particularly impressive faculties, which have long fascinated scientists. For example, it can change its color to blend in perfectly with its environment or imitate the shape of a poisonous animal to deceive its predator. He is even able to use tools and solve complex cognitive puzzles.
He is also able to regenerate severed limbs, these powerful tentacles that he cleverly uses to make him an excellent predator, as well as his hunting arsenal (venom, suction cups, beak, etc.). One might then be tempted to think that there is not much that could outlast this exceptional animal, but strangely enough, its average life span is very short. While some primates and corvids live for decades, shallow-water octopuses, such as the California two-spot octopus (octopus bimaculoidesYou only live one year on average.
Like many other cephalopods, an octopus reproduces only once in its life, after which its life cycle ends. After laying her eggs, the female octopus remarkably begins a process of self-destruction, beginning to fast and mutilating herself, while still being strong enough to incubate her eggs until hatching, before succumbing to her poor health.
According to the new study published in the journal current biologyCaptive-bred females seem to intentionally speed up this process, mutilating themselves and frantically twisting their claws. ” What is remarkable is that they are going through such a progression of change that they seem to have gone insane before they died. Clifton Ragsdahl, a professor of neurobiology at the University of Chicago and one of the study’s authors, said in a press release. Moreover, this “programmed suicide” can also be observed in males, who, when they reach the age of about a year or a year and a half, also stop nursing and end up dying, soon after their females.
Co-led by the University of Washington and Illinois, the new research builds on previous research that showed an octopus’ visual gland was involved in its reproduction and lifespan. This gland is in particular its main neuroendocrine center, whose functional equivalent in vertebrates is the hypothalamus (or pituitary gland). In the female octopus, it was first discovered that after mating, the gland changes in a way that alters cholesterol metabolism, leading to dramatic changes in the steroid hormones produced. Which could explain his suicidal behaviour.
Three biochemical pathways are involved
In 1977, Brandeis University psychologist Jerome Wodensky demonstrated that once the optic glands are removed, the two-pointed Caribbean mother octopuses (priarius octopusThey left their eggs and started feeding again. They then lived several months longer than those still supplied with their glands. Already at that time, scientists realized that the gland probably secretes “self-destructive” hormones, but the metabolic mechanisms that stimulate this phenomenon are not yet fully understood.
To arrive at their findings, the researchers in the new study next sequenced the activated and deactivated genes in the cells of the optic gland of mother octopuses (octopus bimaculoides), in various stages of its decline. Then they noticed that when the cephalopods began to fast, there were higher levels of activity in the genes that metabolize cholesterol and produce steroids.
Cholesterol is already involved in many vital physiological processes in animals, such as cell membrane elasticity and the production of stress hormones.” But it was quite a surprise to see that it also plays a role in this life cycle process Says (referring to octopus self-destruction) Z. Yan Wang, associate professor of psychology and biology at the University of Washington, and lead author of the study.
The research group also discovered three different biochemical pathways related to post-reproductive increases in steroid hormones. The first produces pregnenolone and progesterone, two steroids commonly associated with pregnancy. The other produces maternal cholestanoids or intermediates for making bile acids, and the third results in increased levels of 7-dehydrocholesterol (or 7-DHC), a precursor of cholesterol.
Some of these pathways are also activated for cholesterol production in mice and other mammals. In humans, an elevated level of 7-DHC is toxic. This is a notable phenomenon in Smith-Lemli-Obitz syndrome (a genetic disorder caused by a mutation in the enzyme that converts 7-DHC into cholesterol). Children with this condition have severe developmental and behavioral problems, resulting in frequent self-harm. This behavior is very similar to the behavior seen in octopuses, according to the research group.