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Why do octopuses eat their own bodies after mating?

A research team at the University of Washington has discovered that certain chemicals may be linked to maternal octopus suicide.

California two-spotted octopus near the end of life.  Photo: Z Yan Wang

California two-spotted octopus near the end of life. Image: Z Yan Wang

Many animals die after spawning. But for the mother octopus, the trend is especially alarming. In most species, when the mother octopus’s eggs are about to hatch, it stops eating. It then began to self-destruct by smashing its body against rocks, ripping its own skin, and even eating its own arm.

Now, researchers have discovered the chemicals driving this deadly tendency. After an octopus lays eggs, it undergoes changes in cholesterol production and utilization, leading to increased secretion of steroid hormones. It was the biochemical change that caused it to commit suicide, according to Z. Yan Wang, an assistant professor of psychology and biology at the University of Washington. Wang and colleagues published their findings on May 12 in the journal Current Biology.

Previously, no one knew clearly the purpose of the mother octopus’s suicidal behavior. Theories include death attracting predators away from the nest or the mother octopus’s body releasing nutrients into the water to nourish the eggs. However, according to Wang, it is more likely that the death of the mother octopus will protect the young from the older generation. Octopus has a habit of eating cannibals. If there are older octopuses around, they can eat all of each other’s young.

Wang et al analyzed chemicals produced in the eye glands of the California two-spotted octopus (Octopus bimaculoides) after they lay eggs. In 2018, a genetic analysis of the same species showed that after laying eggs, the gene responsible for steroid hormone secretion in the eye gland begins to accelerate. Therefore, Wang’s research group focused on steroids and related chemicals produced by the eye glands of the two-spotted octopus.

They found three distinct chemical changes occur around the time the mother octopus lays eggs. The first is an increase in pregnenolone and progesterone, two hormones involved in reproduction in a variety of animals. Second, the mother octopus began to produce more 7-dehydrocholesterol (7-DHC). Finally, the eye gland also secretes more bile acid components. Octopuses do not have the same type of bile acids as mammals, but components in this compound may play an important role in controlling the lifespan of invertebrates.

Octopuses are difficult to study in captivity because of the large space required and the perfect conditions for them to grow to maturity and reproduce. Wang and other researchers are looking for ways to feed the Pacific striped octopus (Octopus chierchiae) and mating in the laboratory. Unlike most octopuses, the Pacific striped octopus can mate multiple times and raise multiple eggs. They do not destroy themselves when the eggs are about to hatch, so this is the perfect specimen to study the source of suicidal behavior.

An Khang (According to Live Science)

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