After a female octopus lays a clutch of eggs, she’ll watch over them, protecting them from predators and keeping them oxygenated by routinely dousing them with water. But there’s a dark side to this story. Expectant octopus mothers also stop eating after laying the eggs, and often start to self-mutilate – tearing off their skin or eating their own arms. They'll typically die before the eggs hatch. But why?
In a 2022 study published in Current Biology, researchers found changes in a series of biochemical pathways that may be responsible for the animal’s self-destruction. One of these changes leads to an increase in 7-dehydrocholesterol (7-DHC), a hormonal precursor to cholesterol. The study found three chemical pathways that increase steroid hormones after reproduction. The first produces pregnancy hormones. The other two produce 7-DHC, and bile acid intermediates, neither of which were previously known.
The sad, strange fate of octopus mothers:
- Scientists already knew that the octopus’ optic glands are responsible for this behavior. In previous experiments, scientists have removed the glands, and the octopuses resume eating and live months longer. But the trigger for the behavior was not known.
- In humans, higher-than-normal levels of 7-DHC are toxic, and a sign of a genetic disorder called Smith-Lemli-Opitz syndrome. A mutation in the enzyme that converts 7-DHC to cholesterol causes the disorder, and can lead to self-injurious behavior in children.
- Theories about why this behavior occurs range from drawing predators away from the eggs, the mother's dead body releasing nutrients into the water, and protecting younger octopuses from cannibalistic older ones.