Many animal species die after reproduction. But in octopus mothers, this decline is particularly alarming: in most species, when a mother octopus’ eggs approach hatching, she stops eating. She then leaves her protective platoon on her offspring and leans on self-destruction. She could fight against a rock, tear her skin, even eat pieces of her own arms.
Now researchers have discovered the chemicals that seem to control this deadly frenzy. After an octopus lays eggs, it experiences changes in the production and use of cholesterol in its body, which in turn increases its production of steroid hormones – a biochemical change that will doom it. Some of the changes may hint at processes that explain invertebrate longevity more generally, said Z. Yan Wang, assistant professor of psychology and biology at the University of Washington.
“Now that we have these pathways, we’re really interested in linking them to individual behaviors, or even individual differences in how animals express these behaviors,” Wang told Live Science.
programmed to die
Even as an undergrad studying English, Wang was intrigued by female reproduction, she said. When she made the transition to graduate school in science, she retained that interest and was struck by the dramatic deaths of mother octopuses after laying their eggs. No one knows the purpose of the behavior. Theories include the idea that dramatic death displays keep predators away from the eggs or that the mother’s body releases nutrients into the water that nourish the eggs. Most likely, Wang said, death protects babies of the older generation. Octopuses are cannibals, she said, and if older octopuses stayed, they could end up eating all of the other’s young.
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A 1977 study by Brandeis University psychologist Jerome Wodinsky found that the mechanism behind this self-destruction lay in the optic glands, a set of glands near the octopus’s eyes that is roughly equivalent to the pituitary gland. in man. If the nerves to the optic gland were severed, Wodinsky found, the mother octopus would abandon her eggs, start eating again, and live another four to six months. That’s an impressive life extension for creatures that only live about a year.
But no one knew what the optic gland was doing to control this cascade of self-harm.
“Early on, I was really keen to do the experiments we described in the paper we just published, which basically involves extracting the juice from the optic gland and then identifying the components of that juice,” Wang said.
Wang and his colleagues analyzed the chemicals produced in the optic glands of California two-spotted octopuses (bimaculoid octopus) after laying eggs. In 2018, a genetic analysis of the same species showed that after spawning, the genes in the optic glands that produce steroid hormones (which are built, in part, with components of cholesterol) started to go into overdrive. With this study as a guide, the scientists focused on the steroids and related chemicals produced by the optic glands of two-spotted octopuses.
Fatal Changes
They found three distinct chemical changes that happened around the time the octopus’ mother laid her eggs. The first was an increase in pregnenolone and progesterone, two hormones associated with reproduction in a host of creatures (in humans, progesterone rises for ovulation and during early pregnancy). The second shifts were more surprising. Octopus mothers started producing higher levels of a cholesterol building block called 7-dehydrocholesterol or 7-DHC. Humans produce 7-DHC during manufacturing cholesterol too, but they don’t keep it in their systems for long; the compound is toxic. In fact, infants born with the genetic condition of Smith-Lemli-Opitz syndrome cannot eliminate 7-DHC. The result is intellectual disability, behavioral problems including self-harm, and physical abnormalities like extra fingers and toes and cleft palate.
Finally, the optic glands also began 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 type of bile acids as mammals, but they apparently make up the building blocks of those bile acids.
“This suggests that this is an entirely new class of signaling molecules in the octopus,” Wang said.
The components of bile acids are intriguing, Wang said, because a similar set of acids has been shown to control worm lifespan. Caenorhabditis elegans, which is commonly used in scientific research due to its simplicity. Bile acid components may be important in controlling the longevity of invertebrate species, Wang said.
Octopuses are difficult to study in captivity because they need lots of space and perfect conditions to reach sexual maturity and reproduce. Wang and other octopus researchers have now found a way to keep the lesser Pacific striped octopus (octopus chierchiae) living and reproducing in the laboratory. Unlike most other octopus species, Pacific striped octopuses can mate multiple times and incubate multiple clutches of eggs. They do not self-destruct as their eggs prepare to hatch, making them perfect specimens to study the origin of the morbid behavior.
“I’m really, really excited to study optic gland dynamics in this species,” Wang said.
The researchers published their findings May 12 in the journal Current biology.
Originally posted on Live Science.
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