After mating, female octopuses increase production of a steroid hormone, which may drive them to starve themselves while guarding their eggs
12 May 2022
A steroid hormone may be responsible for making young female octopuses waste away and die soon after laying eggs.
California two-spot octopuses (Octopus bimaculoides) are normally very active predators, but the females starve themselves while guarding their first – and last – clutch of eggs, until they finally die, usually at about 1 year of age.
The octopuses have two optic glands near the optic lobes in their brains, which are considered roughly equivalent to the pituitary gland in humans and other vertebrates. More than four decades ago, researchers discovered that if the octopuses’ optic glands were surgically removed, the animals would abandon their eggs, hunt, eat and even mate again – and this didn’t affect the survival of their offspring.
Scientists have come up with various explanations as to why octopuses have evolved this self-destructive phase in their life cycle. Octopuses frequently cannibalise other octopuses, so one suggestion is that mothers self-destruct to prevent them from eating the younger generation.
It is particularly curious because when creatures have large brains, as octopuses do, they typically have long lifespans, says Z. Yan Wang at the University of Washington in Seattle. “We don’t see that in octopuses, and, in fact, we see something that’s almost aggressively the opposite, because they have this self-destruct system that forcefully ensures they have a short lifespan,” she says.
Wang and her team used mass spectrometry to analyse optic glands and optic lobes in both mated and unmated female octopuses, to better understand the substances that lead to the animals’ early demise.
They found that after mating, the optic glands pump up production of enzymes that convert cholesterol into the steroid 7-dehydrocholesterol (7-DHC).
The glands also produce increased amounts of progesterone – which maintains pregnancy in mammals – and bile acid-like hormones that appear to be unique to octopuses. The precise roles of these substances in the self-destructive processes of octopus mother deaths – and of longevity in general – are unclear, says Wang.
In humans, a genetic condition called Smith-Lemli-Opitz syndrome results in high levels of 7-DHC. The condition is linked to developmental delays and repetitive, self-harming behaviour.
The findings suggest potential links between cholesterol metabolism, neurodegenerative conditions and lifespan, says Wang.
“The important parallel here is that what we see in humans, as well as in octopuses, is that high levels of 7-DHC are associated with lethality and toxicity,” says Wang. “And that, to me, is really interesting, just because of how evolutionarily divergent these two animals are.”
Journal reference: Current Biology, DOI: 10.1016/j.cub.2022.04.043
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