Why do octopuses eat eggs and gnaw their hands?

Many animals die soon after spawning, while the mother octopus eats her eggs when she is about to hatch, then bites herself, eats her arm… Why is that?

The California two-spotted octopus has blue eye circles on the sides.

When the eggs of the octopus are close to hatching, the mother will stop eating her eggs and tend to self-destruct such as throwing herself on rocks, scratching her own skin, even eating her arms.

Now, researchers have discovered chemicals that can control this frenzy of the mother octopus. After an octopus lays eggs, the mother undergoes changes in the production and use of cholesterol in her body, thereby increasing the production of steroid hormones - a biochemical change that will destroy the mother octopus.

Z. Yan Wang, an associate professor of psychology and biology at the University of Washington in the US, said some changes could hint at how to explain longevity in invertebrates in general.

Programming to die

Ever since he was a university student majoring in English, Wang was intrigued by the reproduction of the mother octopus. As she transitioned to graduate school in science, she further studied the death of the mother octopus after laying eggs. Because so far no one knows the purpose of this behavior. Theories suggest that this death is intended to 'distract' predators away from its eggs, or that the mother's body secretes nutrients into the water to nourish the eggs.

Wang thinks, most likely, this death to protect the baby octopus from the old generation. Because octopuses are cannibals, and if old octopuses get stuck around, they can eat the young.

A 1977 study by psychologist Jerome Wodinsky of Brandeis University found the mechanism behind this self-destruction lies in the visual glands, a set of glands near the octopus' eyes (similar to the pituitary gland). in humans). Wodinsky found that if the nerves to the optic gland were cut, the mother octopus would give up her eggs, start eating the eggs, and live another four to six months. That's an impressive lifespan extension for creatures that live only about a year.

In 2018, a genetic analysis of the same species showed that, after laying eggs, the genes in the visual glands that produce steroid hormones (in part built with cholesterol components) begin to develop. exceed. They focused on steroids and related chemicals produced by the visual glands in two-spotted octopuses.

Serious changes

The researchers found three distinct chemical changes that occur around the time the mother octopus lays eggs. The first is an increase in Pregnenolone and progesterone, two hormones involved in reproduction in many organisms.

More surprisingly, the mother octopuses began to produce higher levels of a cholesterol called 7-dehydrocholesterol, or 7-DHC, the toxic compound. In humans, if the mother produces a lot of 7-DHC compounds, the baby will have a child with the genetic disorder Smith-Lemli-Opitz syndrome, which causes the child to have intellectual disability, behavioral problems and physical abnormalities such as extra fingers and toes, and cleft palate.

Finally, the visual glands also begin to produce more components for bile acids, which are acids made by the liver in humans and other animals. Octopuses don't have the same bile acids as mammals, but they do seem to make the building blocks for those bile acids.

The bile acid composition is important for controlling the lifespan of invertebrates, Wang said.