Most octopus species live for one year. But the death of mother octopuses after they reproduce has long been a scientific spectacle.
Why exactly mother octopuses engage in a form of self-harm that leads to death right after breeding remains a mystery. But a study published Thursday in the journal Current Biology uses the California two-spotted octopus as a model to help explain the physiology of this strange behavior.
Z. Yan Wang, assistant professor of psychology and biology at the University of Washington and author of the study, explained that the female of the species goes through three stages of reproduction.
After mating, the mother produces her eggs and handles them with care. She takes each egg, one at a time, carefully threading them into long strands. Then she cements them to the wall of her den and stays there, blowing water over the eggs to keep them oxygenated and fiercely protecting them from predators.
But then she stops eating. She begins to spend a lot of time away from the eggs. She loses color and muscle tone; his eyes are damaged. Many mothers start hurting themselves. Some rub against the gravel of the seabed, scarring their skin; others use their suction cups to create lesions along their body. In some cases, they even eat their own arms.
Scientists have known for some time that octopus reproductive behavior, including death, is controlled by the animal’s two optic glands, which function like the pituitary in vertebrates, secreting hormones and other products. that control various bodily processes. (The glands are called “optic” because of their location between the animal’s eyes. They have nothing to do with vision.) If both glands are surgically removed, the female abandons her brood, resumes eating , grows and has an extended lifespan. .
The new study describes the specific chemical pathways produced by the optic glands that govern this reproductive behavior.
One pathway, they discovered, generates pregnenolone and progesterone, which is not surprising since these substances are produced by many other animals to aid reproduction.
Another produces the bile acid precursors that promote the absorption of dietary fat, and a third produces 7-dehydrocholesterol, or 7-DHC. 7-DHC is also generated in many vertebrates. In humans, it has a variety of functions, including essential roles in the production of cholesterol and vitamin D. But high levels of 7-DHC are toxic and are linked to disorders like Smith-Lemli-Opitz syndrome, a rare inherited disease characterized by severe intellectual, developmental and behavioral problems. In octopuses, Dr. Wang and his colleagues suspect that 7-DHC may be the key factor in triggering the self-harming behavior that leads to death.
Roger T. Hanlon, senior scientist at the Marine Biological Laboratory in Woods Hole, Massachusetts, who was not involved in the study, said that “this is an elegant and original study that addresses a long-standing question. date in the reproduction and scheduled deaths of most octopuses.
Dr Wang said that “for us, what was most exciting was seeing this parallel between octopuses, other invertebrates and even humans.” She added that it was “remarkable to see this shared use of the same molecules in animals far apart from each other”.
The molecules may be the same, but death, she says, is very different. We generally view human death as a failure of organ systems or function.
“But in an octopus, that’s not true,” Dr. Wang said. “The system is supposed to do that.”