Octopuses are among the most unique animals on our planet. Their unusual structure is beyond any other physiology throughout the biodiversity. But behind their evolutionary survival mechanisms such as limb regeneration and color adaptation, many of the octopus population die in the saddest way possible.
Why Octopuses Die After Reproduction
MELBOURNE, AUSTRALIA - NOVEMBER 13: An octopus is seen on November 13, 2020 in Melbourne, Australia. Following the Victorian government's easing of COVID-19 restrictions on indoor entertainment venues, SEA LIFE Melbourne Aquarium opened to the public on Friday with capacity restrictions and extra health and safety measures in place. Guests now have allocated time-slots to visit, physical distancing between groups is encouraged while hygiene screens in various areas and extra cleaning processes have been introduced. All visitors aged 12 and above ale also required to wear face masks.
When a mother octopus lays a batch of eggs, it will refrain from consuming nutrition and continue to weaken for the following days. After the eggs hatch, the mother will die. This behavior is common in many environments. It could also happen with octopuses that are in captivity, and it was observed that they intentionally speed up this process.
Among the most bizarre twists of this behavior from octopuses is that, when they want to end their life faster, the animals mutilate themselves and tangle their remaining limbs.
According to a new study, this behavior is caused by a maternal response that is induced by the optic gland. This gland is parallel to the pituitary glands that mammalian species have.
Throughout the decades of biological studies, the reason behind the tragic deaths of octopuses is unknown. Thanks to the analysis from the scholars from the University of Washington, the University of Chicago, and the University of Illinois Chicago (UIC), the research found that the optic glands of the maternal octopuses are triggered by a kind of activity that pushes it to dramatically change the animal's cholesterol metabolism.
This shift allows a massive change in steroid hormones that the tentacled individuals have, resulting in disruption of their common behavior and longevity processes. The consequences of these changes are also evident in many mammals, including the human species.
The authors believe that this phenomenon offers a glimpse of the importance of steroids, giving a further understanding of how the compound's function influences the lives of many groups across the world's biodiversity, particularly in soft-bodied cephalopods and vertebrates.
Steroids, Cholesterol, and Changes in Optic Glands
Washington's psychology and biology specialist Z. Yan Wang, who also served as lead of the study, explained in a PhysOrg report that the specified cholesterol was already established as a dietary component and responsible for other signaling functions across body functions.
Steroids are frequently involved in several cellular activities such as maintenance of cell membranes and regulation of stress hormones, however, the team was surprised about the compound's significant role in the life cycle process, Wang continued.
The first hints of this behavior in octopuses was first observed in 1977 by Brandeis University psychology specialist Jerome Wodinsky. According to the records, Wodinsky analyzed that if the optic glands of the maternal Caribbean two-spot octopus (Octopus hummelincki), they immediately leave their own eggs to hatch, eat regularly, and retain their life for months.
Through this experiment, cephalopod experts theorized that the optic gland might have some compounds that drive a type of 'self-destruct' hormone, but the details of this substance and how it works remained unknown until today.
In the new study, the authors analyzed a separate species, known as the California two-spot octopuses or Octopus bimaculoides. Through RNA and DNA sequencing, it was discovered that the animals fast and decline through intense gene activities that control steroid production and cholesterol metabolism.
It was concluded that the activity increases pregnancy-related steroids such as pregnenolone and progesterone, as well as maternal cholestasis (for bile acids), and precursor of cholesterol known as 7-dehydrocholesterol (7-DHC).
The study was published in the journal Current Biology, titled "Steroid hormones of the octopus self-destruct system."
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