Most octopus species live for a year. But the deaths of female octopuses after they reproduce have long been a scientific spectacle.
Why exactly octopus mothers practice a form of self-mutilation that leads to death shortly after breeding remains a mystery.
But a study published today in the journal Current Biology uses the California 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 work, explained that the female of the species goes through three reproductive stages.
After mating, the female produces the eggs and takes care of them carefully. She takes each egg, one by one, and carefully ties them together in long rows. She then glues 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. Begins to spend a lot of time away from eggs. She loses color and muscle tone; her eyes are damaged. Many mothers start to get hurt. Some rub on the gravel of the sea floor, injuring their skin; others use their suction cups to create lesions along their bodies. In some cases, they even eat their own tentacles.
Scientists have known for some time that the octopus’ reproductive behavior, including death, is controlled by the animal’s two optic glands, which function like the pituitary or pituitary gland 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 the litter, starts eating again, grows back. and has a longer life.
The new study describes specific chemical pathways produced by the optic glands that govern this reproductive behavior.
One pathway, they found, generates pregnenolone and progesterone, which is not surprising because these substances are produced by many other animals to support reproduction.
Another produces the bile acid precursors that promote the absorption of dietary fats, and a third produces 7-dehydrocholesterol, or 7-DHC. 7-DHC is also generated in many vertebrates. In humans, it has several functions, including essential roles in the production of cholesterol and vitamin D. But high levels of 7-DHC are toxic and linked to disorders such as Smith-Lemli-Opitz syndrome, a rare hereditary disease characterized severe intellectual, developmental and behavioral problems.
In octopuses, Wang and his colleagues suspect that 7-DHC may be the key factor in triggering the self-mutilation behavior that leads to death.
Roger T. Hanlon, a senior scientist at the Woods Hole Marine Biology Laboratory in Massachusetts, who was not involved in the study, said, “This is an elegant and original study that addresses an age-old question linked to reproduction and programmed death in most of octopuses”.
Wang said, “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 the shared use of the same molecules in animals that are very far apart.”
The molecules may be the same, but death is different, she said. We generally see human death as a failure of organ systems or functions. “But in an octopus that’s not true,” Wang said. “The system itself would be causing it.”
Translated by Luiz Roberto M. Gonçalves.
