Most octopus species live for one year. But the death of octopus mothers after reproducing has long been a scientific spectacle.
Why exactly octopus mothers engage in a form of self-harm that leads to death right after reproducing remains a mystery. But a study published Thursday in the journal Current Biology uses the California two-spot octopus as a model to help explain the physiology of this strange behavior.
Z. Yan Wang, an assistant professor of psychology and biology at the University of Washington and an author of the study, explained that the female of the species goes through three reproductive stages.
After mating, the mother produces her eggs and handles them carefully. She takes each egg, one by one, carefully threading them into long strands. She then cements them to the wall of her den and she stays there, blowing water on the eggs to keep them oxygenated and fiercely protecting them from predators.
But then he stops eating. She begins to spend a lot of time away from the eggs. She loses color and muscle tone; her eyes are damaged. Many mothers begin to injure themselves. Some rub against the gravel of the seabed, leaving scars on their skin; others use their suckers to create lesions throughout their bodies. In some cases, they even eat their own arms.
Scientists have known for some time that reproductive behavior in the octopus, 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 body 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 young, she begins to eat again, grows, and lives a long life. .
The new study describes specific chemical pathways produced by the optic glands that govern this reproductive behavior.
They found that one pathway generates pregnenolone and progesterone, which is not surprising, because these substances are produced by many other animals to support reproduction.
Another produces 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 roles, including essential roles in cholesterol and vitamin D production. But elevated levels of 7-DHC are toxic and linked to disorders such as Smith-Lemli-Opitz syndrome, a rare inherited disease characterized by severe intellectual, developmental, and behavioral problems. In octopuses, Dr. Wang and her colleagues suspect that 7-DHC may be the essential factor in triggering self-injurious 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, “This is an elegant and original study that addresses a long-standing question in the reproduction and programmed deaths of most octopuses.
Dr Wang said that “for us, the most exciting thing was seeing this parallel between octopuses, other invertebrates and even humans.” He added that it was “remarkable to see this sharing of the same molecules in animals that are very distant from each other.”
The molecules may be the same, but death, he said, is very different. We generally see human death as a failure, of organ systems or of function.
“But in an octopus that’s not true,” Dr. Wang said. “The system is supposed to be doing this.”