New research has found that elevated levels of a cholesterol precursor that drives self-destructive behavior in humans also leads to the programmed suicide of octopus mothers after reproduction.
For all their amazing intelligence and seemingly supernatural abilities to change color and regrow limbs, octopuses often die tragic deaths.
After a mother octopus lays a clutch of eggs, she stops eating and is consumed. When the eggs hatch, she is already dead.
Some captive females even seem to speed up this process intentionally, mutilating themselves and twisting their tentacles into a tangle that inevitably leads to their death.
The source of this strange maternal behavior seems to be the optic glandan organ similar to the pituitary gland present in mammals.
For years, it hasn’t been known how this gland triggers the gruesome death spiral, but a new study by researchers at the University of Chicago, the University of Washington, and the University of Illinois Chicago (UIC) shows that the optic gland in maternal octopuses undergoes a massive change in the cholesterol metabolismcausing dramatic changes in the animal’s steroid hormones that trigger its fatal behavior.
Alterations in cholesterol metabolism in other animals, including humans, can have serious consequences for longevity and behavior.
The study authors believe this reveals important similarities in the functions of these steroids across the animal kingdom, in both soft-bodied cephalopods and vertebrates.
“We know that cholesterol is important from a dietary perspective and also within different signaling systems in the body,” he explains. Z.Yan Wanglead author of the study.
“It’s involved in everything from the flexibility of cell membranes to the production of stress hormones, but it was a big surprise to see that it also played a role in this life cycle process.”
In 1977, Brandeis University psychologist, Jerome Wodinskishowed that if the optic gland was removed from two-spotted Caribbean octopus mothers (Octopus hummelincki), they abandoned their clutch of eggs, returned to feed and lived for months more.
At the time, cephalopod biologists concluded that the optic gland must secrete some kind of “self-destruct” hormone, but what it was and how it worked was unclear.
In 2018, Wang, and Clifton Ragsdalea professor of neurobiology at UChicago, sequenced the RNA transcriptome of the optic gland of several California two-spot octopuses (Octopus bimaculoides) at different stages of development from their maternal decline.
RNA carries instructions from DNA on how to make proteins, so sequencing it is a good way to understand gene activity and what’s going on inside cells at any given time.
As the mother octopuses in this research began to fast and decay, there were higher levels of activity in the genes that metabolize cholesterol and produce steroids. It was the first time that the optic gland had been linked to something other than reproduction.
One more step
In new research, the results of which are published in Current Biology, Wang and Ragsdale took their studies a step further and looked at chemicals produced by the maternal octopus’ optic gland.
Since Wang’s earlier research pointed to increased activity in steroid-producing genes, they focused on cholesterol and related molecules in optic gland tissue.
discovered three different ways involved in the rise of steroid hormones after reproduction. One of them produces pregnenolone and progesterone, two steroids commonly associated with pregnancy.
Another produces maternal cholestanoids or bile acid intermediates, and the third pathway produces elevated levels of 7-dehydrocholesterol (7-DHC), a precursor of cholesterol.
The new research shows that the maternal optic gland undergoes dramatic changes to produce more pregnenolone and progesterone, maternal cholestanoids, and 7-DHC during stages of decline.
While pregnancy hormones are to be expected, this is the first time that bile acid or cholesterol components have been linked to the maternal octopus death spiral.
Some of these same pathways are also used to make cholesterol in mice and other mammals, the researchers note.
“There are two main pathways for cholesterol creation that are known from rodent studies, and there is now evidence from our study that those pathways are probably present in octopuses as well,” Wang said. “It was really exciting to see the similarity.” between such different animals”.
High levels of 7-DHC are toxic to humans. It is the hallmark of a genetic disorder called Down syndrome. Smith-Lemli-Opitz (SLOS)which is caused by a mutation in the enzyme that converts 7-DHC to cholesterol.
Children with this inherited and congenital disorder suffer serious developmental and behavioral consequences, including repetitive self-harm reminiscent of octopus end-of-life behaviors.
The findings suggest that disruption of the cholesterol production process in octopuses has serious consequences, just as it does in other animals.
What Wang and his team have discovered is another step in the octopus’s self-destruct sequence, indicating further changes later that ultimately lead to the strange behavior and death of the mother.
“The amazing thing is that they go through this progression of changes where they seem to go crazy right before they die,” Ragsdale said.
“Maybe it’s two processes, maybe three or four. Now, we have at least three apparently independent pathways to steroid hormones that could explain the multiplicity of effects these animals show.”
The researchers will further this discovery using another species of octopus (chierchiae), also known as the lesser Pacific striped octopus, which is not destroyed after reproduction.
Wang plans to examine the optic glands of this octopus species and compare them to his new results for clues on how to avoid the octopus’s tragic death spiral.
Steroid hormones of the octopus self-destruct system. Z. Yan Wang et al. Current Biology, May 12, 2022. DOI:https://doi.org/10.1016/j.cub.2022.04.043