SCIENCE OCTOPUS SCHEMES

Short-Lived Motherhood

The trigger that makes an octopus mom self-destruct.

Most octopus species live for one year. But the death of octopus mothers after they reproduce have long been a scientific spectacle. Why exactly octopus mothers engage in a form of self-harm that leads to death just after they reproduce remains something of a mystery.

But a new study uses the California two-spot octopus as a model to help explain the physiology of this strange behaviour.

Scientists have known that reproductive behaviour in the octopus, including death, is controlled by its two-optic glands, which function like the pituitary in vertebrates, secreting hormones and other products that control various bodily processes.

If both glands are surgically removed, the female abandons her brood, begins eating again, grows and has an extended life span.

The new study describes specific chemical pathways produced by the optic glands that govern this reproductive behaviour.

One pathway, they found, generates pregnenolone and progesterone, which is unsurprising, because these substances are produced by many other animals to support reproduction.

Another produces precursors of bile acids that promote absorption of dietary fats, and a third makes 7-dehydrocholesterol, or 7-DHC, which is generated in many vertebrates as well. 

In humans, it has various functions, including roles in the production of cholesterol and vitamin D. But elevated levels of 7-DHC are toxic, and are linked with certain disorders.

In octopuses, researchers suspect that 7-DHC may be the essential factor in triggering the self-harming behaviour that leads to death. [Nicholas Bakalar]