Octopuses are fantastic animals. They demonstrate phenomenal puzzle-solving skills and are adored by the Internet. They are also very mysterious creatures but scientists are slowly managing to unravel their secrets.
An important characteristic that has been investigated has to do with the end of an octopus' life. Octopuses are semelparous animals, meaning that they reproduce once and then die. This death is particularly dramatic for female octopuses, and they have been seen harming themselves in captivity to speed up the process.
In the 70s this behavior was linked to the optic gland and now researchers have discovered several distinct chemical signals that control four separate phases of maternal behavior and then lead to the animal's demise. The research is published in the Journal of Experimental Biology.
"We're bringing cephalopod research into the 21st century, and what better way to do that than have this unveiling of an organ that has historically fascinated cephalopod biologists for a long, long time," lead author Z. Yan Wang, from the University of Chicago, said in a statement.
"These behaviors are so distinct and so stereotyped when you actually see them. It's really exciting because it's the first time we can pinpoint any molecular mechanism to such dramatic behaviors, which to me is the entire purpose of studying neuroscience."
The team studied female two-spot octopuses at different times during their reproductive cycle. Mature non-mated females are active predators spending little time in their dens. But after they lay their eggs their behavior changes dramatically. For the first three or four days, they stay near their eggs and continue to eat, grabbing crabs that get too close. Then they stop eating altogether for about eight to 10 days. In the final phase, they hit themselves against the sides of their tanks (if in captivity), and lose muscle tone and color thanks to a lack of nutrition.
"This is troubling to even witness in the lab because from a human perspective they look like they're self-mutilating. It's just very, very strange behavior," Wang stated.
The researchers collected samples from the optic glands of octopuses at each stage of the process and worked out what proteins were being produced at the time. Before reproducing, they have a high level of neuropeptides, proteins used by nerve cells to communicate. These are linked to feeding behavior in many animals. After they lay their eggs, these proteins drop off. Different molecules are produced after reproduction but how they cause the change in behavior is not exactly clear.
It’s also not certain why this fate evolved in octopuses. It could be to prevent mothers eating their young or to reduce competition for resources. It might seem grim to us but it seems to work for them.