WuXi AppTec Content Team Editor
Octopuses can be regarded as one of the solitary creatures, and after they are born, they are destined to face the dangerous environment alone.
First, female octopuses gradually stop eating and self-mutilate after spawning, peeling off their skin and biting off the tips of their tentacles. By the time the baby octopus was born, its mother had already died. The missing father also dies months after mating is complete.
Therefore, it is basically impossible for the tadpole to find its mother in the octopus.
▲The special post-reproductive behavior of octopuses has always fascinated scientists | Reference [2], credit: Tom Kleindinst, Marine Biological Laboratory
The amazing post-reproductive suicidal behavior of octopuses has also fascinated many biologists. Initially, the researchers speculated that the mating process triggers a self-destruction mechanism in octopuses. Of course, this is all speculation.
Recently, decades after hypotheses, some scientists have finally found evidence of a partial self-destruct mechanism. Researchers at the University of Chicago found that some cholesterol-related signaling pathways are altered when octopuses mate, which can affect the levels of various hormones.
▲Research paper published in the open access journal Current Biology
Cholesterol itself is an important part of the diet, and it is involved in many cellular functions, from the toughness of cell membranes to the production of stress hormones.
However, excessive levels of cholesterol precursors are cytotoxic, so hyperactive cholesterol metabolism can also cause serious developmental and behavioral problems, such as repetitive Self-harm or feeding disorder. This seems to be very similar to the behavior of female octopuses after spawning.
▲Cholesterol metabolism and related hormones may influence female octopus suicidal behavior | Reference [2]
With this question in mind, Dr. Z. Yan Wang, a molecular biologist at the University of Chicago, decided to look for a possible cholesterol mechanism.
Here I have to mention a special organ in octopuses called optic gland, which was discovered in 1977, and some follow-up studies have found that the function of the optic gland is somewhat Similar to the human pituitary gland and is able to influence the sexual development and aging process of octopuses.
If the optic glands are removed from the female octopus before mating, they can survive for several months after spawning. This suggests that the presence of optic glands likely influenced post-mating behavior.
▲The optic gland is likely to play a key role in suicidal behavior | Source: Reference [2]
The authors have previously found that genes that control sex hormone and cholesterol metabolism are more active when octopuses are dying. So they removed the optic glands before and after the octopus mating for a detailed analysis, and found that once the mating behavior occurs, the optic glands begin to secrete a large amount of sex hormones and cholesterol precursors, as well as insulin-like hormones.
Photocholesterol precursors do enough damage, and the combination of the three molecules helps initiate a cascade of death signals. As the optic glands continue to secrete three kinds of molecules, the self-destruction signal received by the octopus continues to strengthen, and finally begins to choose self-termination after reaching the threshold.
Although scientists already knew that the optic gland was involved in octopus sex hormone secretion, it is the first time that two other molecules, as well as the optic gland’s link to suicidal behavior, have been shown.
Clifton Ragsdale, a neurobiologist at the University of Chicago, said: “Octopuses seem to be dysfunctional before they die, and these processes they go through lead to this result.” There may be other , but it is now certain that cholesterol and related derived molecules play a role in it.
References
[1] Octopuses Tragically Destroy Themselves After Mating. We May Finally Know Why. Retrieved May 13th, 2022 from https:https://www.sciencealert.com/scientists-close-in-on-why-octopuses-tragically-destroy-themselves-after-mating
[2] Steroid hormones of the octopus self-destruct system. Current Biology (2022). DOI:10.1016/j.cub.2022.04.043
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