Study explains why octopus mothers kill themselves after reproduction

Many animals, including octopuses, die after breeding. In most octopus species, the mother stops eating when the eggs are about to hatch.

Scientists have observed that the octopus leaves its protective huddle over its brood and becomes self-destructive. Scientists also report that during this time, the octopus rams itself against rocks and gravel, inflicting wounds on itself that do not heal. Some octopuses over-groom and peel off their skin, while others bite their suckers and consume their own arms.

Scientists have successfully discovered the chemicals that appear to control this deadly behavior. The group explained that after egg-laying, the production and use of cholesterol in their bodies changes. This increases the production of steroid hormones.

Z. Yan Wang, assistant professor of psychology and biology at the University of Washington, explained that some of the changes may bear resemblance to processes that explain longevity in invertebrates.

Wang added that the pathways may be associated with individual differences in the way the animals express their behavior.

Death After Giving Life

Over the years, there have been several theories about why the octopus mother kills herself, including the idea that traumatic death displays keep predators away from the eggs. Other theories suggest that the mother's body releases nutrients into the water that can nourish the eggs.

However, Wang suspects that the mother's death protects the babies from the older generation. She added that octopuses are cannibals and that if old octopuses are still around, they could end up consuming all of their offspring.

The Urge to Self-Destruct

Jerome Wodinsky, a psychologist at Brandeis University, found the mechanism behind self-destruction in the optic glands. His 1977 study found a set of glands near the octopuses' eyes that roughly correspond to the pituitary gland in humans.

Wodinsky discovered that when the nerves to the optic gland are severed, the octopus mother leaves her eggs, begins feeding again, and lives for another 4 to 6 months. The normal life span of the two-spot octopus species is only one year.

However, scientists are still not sure what the optic gland did to control this spate of self-injury among octopus mothers.

The Toxicity

Wang's experimental procedure involved juicing the optic gland and then identifying the components of the extracted juice.

In 2018, the team performed a genetic analysis of the same species, which revealed that after egg laying, there is an overproduction in the optic glands that produce steroid hormones with cholesterol components.

The group found three distinct chemical shifts that occurred around the time the octopus mother laid her eggs. The first shift was an increase in hormones associated with reproduction, namely pregnenolone and progesterone.

The second shift was the production of higher levels of a cholesterol-building block called 7-dehydrocholesterol, or 7-DHC.

Humans produce 7-DHC when they make cholesterol, but they do not keep the substance in their bodies for long because it is toxic. Humans that can't clear seven DHC are more prone to behavioral problems, which include self-injury.

The third shift is the production of the components of bile acids. Wang explained that these same bile acid components have been shown to control the longevity of the worm Caenorhabditis elegans.