After mating, many female octopuses enter a behavioral spiral that causes them to obsessively brood their eggs, stop eating, and eventually die of starvation before their eggs hatch. A study of California two-spot octopuses (Octopus bimaculoides) published last week (May 12) in Current Biology links the strange maternal behavior to changes in cholesterol metabolism that ramp up the production of certain steroids.
“[T]his is an elegant and original study that addresses a longstanding question in the reproduction and programmed deaths of most octopuses,” Roger Hanlon of the Marine Biological Laboratory in Woods Hole, Massachusetts, tells The New York Times. Hanlon was not involved in the study.
More than 40 years ago, scientists connected this self-harming behavior to two optic glands, which are named for their location between the eyes and are not associated with vision, instead being analogous to pituitary glands in humans and vertebrates. Specifically, the team surgically removed the glands and found that the females abandoned their eggs, continued to eat, and lived for months longer than females with the glands, according to a press release about the new study from the University of Washington. The work begins to answer questions of how, exactly, these glands contribute to the behavior.
The research team used mass spectrometry to monitor what chemicals the optic glands produced. According to the study, the researchers identified three biochemical pathways that increase steroid hormone production after the female octopuses mate.
One pathway produced pregnenolone and progesterone, which the press release notes is commonly associated with pregnancy in other animals. Another pathway produced intermediate compounds called maternal cholestanoids that make bile acids. And the third pathway produced high levels of 7-dehydrocholesterol (7-DHC), a precursor to cholesterol.
In humans, a mutation in an enzyme that converts 7-DHC to cholesterol causes the genetic disorder Smith-Lemli-Opitz syndrome. Children with this syndrome have higher than normal levels of 7-DHC and suffer from physical and intellectual developmental issues that can sometimes lead to self-harming behaviors.
“The findings suggest that disruption of cholesterol production process in octopuses has grave consequences, just as it does in other animals,” the press release reads.
“The important parallel here is that what we see in humans, as well as in octopuses, is that high levels of 7-DHC are associated with lethality and toxicity,” study coauthor Z. Yan Wang, a neuroscientist at the University of Washington, tells New Scientist.