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I've read that unlike humans, octopuses have eyes "designed" the "right way", i.e. with the nerve fibers behind the retina, thus getting rid of the blind spot we humans have as well as theoretically improving eyesight.
Have there been tests to compare octopus sight with that of humans, and do they indeed have better vision than us?
There are a couple of advantages and disadvantages of possessing the eyes of octopuses.
The first advantage of the octopus eye is that it has no blind spot. This means that octopuses can see everything that is going on in their environment, and are more aware of predators and prey than some vertebrates. Also, they have many more photoreceptors than vertebrates, at roughly 20,000-50,000/mm2 which means that their vision is much better than that of any human.
The disadvantage of the octopus eye is that it can not see in colour. The eyes possess no cones, only the invertebrate equivalent of rods. This means that octopuses can only distinguish between light and dark.
Adding to the answer above, another advantage of cephalopod eyes is the lower risk of retina detachment. (HumanEvolution)
Also, cephalopod eye focus image by moving the lense (like a camera or telescope), not by changing the lense's curvature, as in vertebrate eye (Wiki). Hence, I speculate that cephalopod would not experience either myopia or hyperopia. Cephalopod may still have problem with presbyopia at old age, affecting both near and far vision, however.
Furthermore, this article comparing human and cephalopod eyes might be of interest: QuarkPhysics
Octopuses are amazing survivors. Here are some of the tricks they use to help them stay alive
You're in the ocean, with sharks and other predators wanting to make a tasty snack out of you. How would you avoid death or injury?
Like us humans, soft-bodied octopuses look relatively defenceless — they have no protective hard shells like their snail and clam cousins.
Instead, they've evolved sophisticated strategies to survive and outwit their predators.
And while their alien-like body may seem the stuff of nightmares, their intelligence and beauty is nothing short of awesome.
Octopuses Have Alternating Sleep States Like Humans, Study Finds
(CN) — The rapid color changes of a sleeping octopus indicate two major alternating sleep states, according to a new study published in the journal iScience.
Like humans, octopuses have two stages of sleep: active and quiet, researchers at the Brain Institute of the Federal University of Rio Grande do Norte, Brazil, discovered. It is during the active state that color changes pulse across their skin, signaling the possibility that the most intelligent of the cephalopods may even dream — a characteristic long thought limited to mammals, birds and select reptiles, including the bearded dragon.
“That led us to wonder whether we might see evidence of two sleep states in octopuses, too,” senior author Sidarta Ribeiro said. “Octopuses have the most centralized nervous system of any invertebrate and are known to have a high learning capacity.”
For years, scientists have known that octopuses have a complex nervous system and are among the most intelligent of all invertebrates. The discovery that these soft-bodied shape shifters have sleep cycles could expand human understanding of the evolution of sleep.
To reach this conclusion, researchers made video recordings of four Octopus insularis in a lab. The videos demonstrated that during “quiet sleep,” the octopuses were still and quiet, their skin pale and eye pupils contracted to a slit. However, during “active sleep,” the cephalopods dynamically changed their skin color and texture as they moved their eyes while contracting their suckers and body with muscular twitches.
“What makes it more interesting is that this ‘active sleep’ mostly occurs after a long ‘quiet sleep’ —generally longer than 6 minutes,” Ribeiro said.
The cycle would repeat every 30 minutes or so.
To ensure the octopuses were sleeping, researchers used visual and tactile stimulation tests to measure the animals’ arousal threshold. In both sleep states, the octopuses needed a strong stimulus to evoke a behavioral response, researchers found.
The alternating sleep states seemed similar to human sleep, despite the enormous evolutionary distance between cephalopods and vertebrates, whose lineages diverged around 500 million years ago, according to first author and graduate student Sylvia Medeiros of the Brain Institute of the Federal University of Rio Grande do Norte, Brazil.
“If in fact two different sleep states evolved twice independently in vertebrates and invertebrates, what are the essential evolutionary pressures shaping this physiological process?” Medeiros said. “The independent evolution in cephalopods of an ‘active sleep’ analogous to vertebrate REM sleep may reflect an emerging property common to centralized nervous systems that reach a certain complexity.”
Intriguingly, the findings raise the possibility that octopuses experience something similar to dreaming.
“It is not possible to affirm that they are dreaming because they cannot tell us that, but our results suggest that during ‘active sleep’ the octopus might experience a state analogous to REM sleep, which is the state during which humans dream the most,” explains Medeiros.
If octopuses dream, it is unlikely that they experience complex symbolic plots like humans do, Medeiros points out. Considering that the “active sleep” stage typically lasts no longer than a minute, their dreams are more likely similar to short videoclips or even GIFs.
In future studies, researchers hope to record neural data from cephalopods to better understand what happens when they sleep. They also intend to probe the role of sleep in the octopuses’ metabolisms, thinking and learning while answering such questions as whether octopuses have nightmares and if their dreams are inscribed on their dynamic skin patterns.
“It is tempting to speculate that, just like in humans, dreaming in the octopus may help to adapt to environmental challenges and promote learning,” Ribeiro says.
How is an Octopus Smarter than a Fifth Grader?
Octopuses, along with many other marine-living animals like dolphins and whales, have been studied and compared to humans. Their behaviours and skills are often observed and tested extensively in order to understand the true nature of these creatures. The impressive abilities of an octopus includes its behavioural patterns, morphological innovations, and cognitive abilities.
With regards to their behavioural patterns, octopuses are relatively anti-social creatures, spending their short five year life span learning how to find food, avoid predators, and react to their environment independently, versus a fifth grader, presumably of ages ten to eleven, who are still in full reliance of a parent or guardian. In this sense, an octopus’ ability to receive, process, and respond to information is much faster than a fifth grader, promoting the fact that they are indeed more intelligent.
Morphologically, octopuses have exceptional eye sight. They cannot see in colour like humans can however, they have no blind spot and can see a full 360 degrees, which makes them have more advanced eyesight than humans do (Byrne et al. 2006). This allows octopuses to choose which arm is closest to the object they want to grasp instead of choosing a limb on the other side of their body (Byrne et al. 2006).
http://biol1210.trubox.ca/wp-content/uploads/sites/84/2016/04/Octopus-Red-Arm.jpg. 2016. [accessed 2016 Apr 4]
When it comes to movement and coordination, the motor skills of an octopus tend to be better than that of a developing fifth grader. In order for their eight limbs to not become entwined, octopuses have many neurons, a total of 500 million large neurons throughout the body the majority of which are found in their arms. Furthermore, octopuses can and have shown limb preferences, which is something that not many animals that have multiple limb pairs usually exhibit (Byrne et al. 2006). Having limb preference is believed to be partially linked to octopus’ vision abilities (Byrne et al. 2006). Octopuses can move in any direction, and they have an overall higher self/physical awareness then a child who is still developing and growing into their own body.
Similar to humans, an octopus can move in a point to point motion by temporarily turning their arms into quasi-jointed structures, which means creating three different bends to act as joints, thus reducing the degrees of freedom problem (Sumbre 2005). This creates some stiffness which allows them to have better control over their arms. Octopuses have suction cups all over their arms which is what they use to grasp their food. They create a pincer grasp between any two suckers on their arms, which is the same motion humans do with their thumb and fingers (Borrell 2009). An octopus is able to dynamically change the organization of their quasi-jointed structure depending on where their sucker is positioned (Sumbre 2005). It is amazing how an octopus can adapt in this way without the help of many mechanisms we have as humans.
https://www.google.ca/search?q=octopus&rls=com.microsoft:en-CA:IE-Address&source=lnms&tbm=isch&sa=X&ved=0ahUKEwj5oM3XgvTLAhXIsIMKHQe3BIIQ_AUIBygB&biw=1699&bih=851#tbm=isch&q=octopus+sucker&imgrc=JUxmjHDvGxApPM%3A. 2016. [accessed 2016 Apr 4]
Along with their morphological advantages, octopuses have impressive cognitive abilities. Scientists and researchers alike have been able to condition and teach octopuses how to solve simple puzzles and mazes, according to the journal of Jennifer A. Mather, under the title of the Cephalopod Specialities. They discovered areas of their brains that allow for more complex functions, by storing away “learned information”, such as simple puzzle solving skills. The neutral substrate generates the consciousness octopus need in order to develop and apply these skills (Mather et al 2013). As a result, octopus have the ability to problem solve and plan.
Their memories can be extensive as well. A study entitled Learning and memory in Octopus vulgaris by I. Zarella et al, talks and compares their memory to that of a human. Octopus can store and recall memory like humans. They also have the ability remember both short and long term memory. Their memory ability aids in helping them learn how to problem-solve and plan. Their long-term memory tends to be activity dependent. Once they have been taught then it is easy for them to remember. It is not so different from average school-aged children, who must go through the motions and learning in order to store it away for later.
Through behavioural patterns, morphological innovations, and cognitive abilities, our research suggests that octopuses contain abilities equal to and greater than that of a fifth grader. They know how to respond to their environment, hunt for food, and survive. Physically, they can grasp things with their “hands” and see with their camera-like eyes (Albertin et al 2015), both of which do not come with ease for humans until a little after birth. Octopuses, like your average fifth-grader, can be taught. They pick up on skills and can store them away for future reference. If they continue to adapt and grow this way, octopuses have the potential to become even smarter than a fifth-grader.
Octopuses have two alternating sleep states, study shows
An octopus in active sleep. Credit: Sylvia L. S. Madeiros
Octopuses are known to sleep and to change color while they do it. Now, a study publishing March 25 in the journal iScience finds that these color changes are characteristic of two major alternating sleep states: an "active sleep" stage and a "quiet sleep" stage. The researchers say that the findings have implications for the evolution of sleep and might indicate that it's possible for octopuses to experience something akin to dreams.
Scientists used to think that only mammals and birds had two sleep states. More recently, it was shown that some reptiles also show non-REM and REM sleep. A REM-like sleep state was reported also in cuttlefish, a cephalopod relative of the octopus.
"That led us to wonder whether we might see evidence of two sleep states in octopuses, too," says senior author Sidarta Ribeiro of the Brain Institute of the Federal University of Rio Grande do Norte, Brazil. "Octopuses have the most centralized nervous system of any invertebrate and are known to have a high learning capacity."
To find out, the researchers captured video recordings of octopuses in the lab. They found that during 'quiet sleep' the animals were still and quiet, with pale skin and eye pupils contracted to a slit. During 'active sleep,' it was a different story. The animals dynamically changed their skin color and texture. They also moved their eyes while contracting their suckers and body with muscular twitches.
"What makes it more interesting is that this 'active sleep' mostly occurs after a long 'quiet sleep'—generally longer than 6 minutes—and that it has a characteristic periodicity," Ribeiro says.
The cycle would repeat at about 30- to 40-minute intervals. To establish that these states indeed represented sleep, the researchers measured the octopuses' arousal threshold using visual and tactile stimulation tests. The results of those tests showed that in both 'active' and 'quiet sleep' states, the octopuses needed a strong stimulus to evoke a behavioral response in comparison with the alert state. In other words, they were sleeping.
An octopus in quiet sleep and active sleep. Credit: Sylvia S L Madeiros
The findings have interesting implications for octopuses and for the evolution of sleep. They also raise intriguing new questions.
"The alternation of sleep states observed in the Octopus insularis seems quite similar to ours, despite the enormous evolutionary distance between cephalopods and vertebrates, with an early divergence of lineages around 500 million years ago," says first author and graduate student Sylvia Medeiros of the Brain Institute of the Federal University of Rio Grande do Norte, Brazil.
"If in fact two different sleep states evolved twice independently in vertebrates and invertebrates, what are the essential evolutionary pressures shaping this physiological process?" she asks. "The independent evolution in cephalopods of an 'active sleep' analogous to vertebrate REM sleep may reflect an emerging property common to centralized nervous systems that reach a certain complexity."
Medeiros also says that the findings raise the possibility that octopuses experience something similar to dreaming. "It is not possible to affirm that they are dreaming because they cannot tell us that, but our results suggest that during 'active sleep' the octopus might experience a state analogous to REM sleep, which is the state during which humans dream the most," she says. "If octopuses indeed dream, it is unlikely that they experience complex symbolic plots like we do. 'Active sleep' in the octopus has a very short duration—typically from a few seconds to one minute. If during this state there is any dreaming going on, it should be more like small videoclips, or even gifs."
In future studies, the researchers would like to record neural data from cephalopods to better understand what happens when they sleep. They're also curious about the role of sleep in the animals' metabolisms, thinking, and learning.
"It is tempting to speculate that, just like in humans, dreaming in the octopus may help to adapt to environmental challenges and promote learning," Ribeiro says. "Do octopuses have nightmares? Could octopuses' dreams be inscribed on their dynamic skin patterns? Could we learn to read their dreams by quantifying these changes?"
How do octopus change color?
Octopuses have specialized cells below their skin surface known as chromatophores. Each chromatophore has a stretchy sac called the cytoelastic sacculus at its center. Each of these sacs is filled with pigments of different colors&mdashred, yellow, black or brown.
Thus, when an octopus tightens its muscles, the pigment sac is pulled wider. This makes the pigments more visible on the skin of the octopus. When the muscles are relaxed, the pigment sac shrinks back to its normal size and the pigments are less noticeable, so the octopus returns to its original, unchanged color.
Can you spot the octopus in this photograph? (Photo Credit: marketa1982/Shutterstock)
Each of the chromatophore cells in an octopus is attached to a nerve. The tightening and relaxation of the cells are controlled by the octopus&rsquo nervous system. Thus, when an octopus wants to camouflage itself, its brain signals the chromatophores to expand in an instant!
Visual Fields and Eye Movements
The eyes of octopus are placed laterally and can be moved independently, with the eye axes occasionally deviating by up to 180 degrees (Heidermanns, 1928). To date, no measurements of visual field size are available for this species. From the eye placement of octopus, one could assume that octopus possesses a small binocular visual field, to the front and possibly to the back however, Budelmann et al. (1997) dispute the existence of a binocular field in octopods. In any case, octopus certainly has large monocular visual fields, the space in which objects can be seen with one eye. This is consistent with the animals watching or tracking objects preferable with one eye (Heidermanns, 1928 Muntz, 1963 Byrne et al., 2002, 2004). The size of the monocular visual field is likely similar to that of Sepia officinalis. Model calculations in Sepia revealed that the visual field is limited by pupil size and that it is much smaller (Schaeffel et al., 1989) than the 177 degrees estimated by Messenger (1968b) for the horizontal plane.
The octopus can modify the space it can oversee by retracting and bulging out its eyes, or by rotational eye movements. The rotational eye movements that can turn the eye up to 80 degrees sideways in either direction (Budelmann and Young, 1984) are mediated by four oblique muscles that pass halfway around the eyeball. In total, each octopus eye has seven extra-ocular muscles, each innervated by a separate nerve (Glockauer, 1915 Budelmann and Young, 1984). In contrast, decapod cephalopods have up to 14 eye muscles that are innervated by only four nerves (Glockauer, 1915 Budelmann and Young, 1993).
Octopus also shows reflexive eye movements. When stimulated by a large field vertical grating rotating on an optokinetic drum, the animals perform compensatory eye, head, and body movements (Packard, 1969).
Future studies of the visual fields of octopus are highly desirable, particularly those that provide measurements of the putative binocular visual field and evaluate its implications for binocular depth perception, the monocular visual field, and the dynamic visual field, taking eye movements into account. Regarding eye movements, it remains to be determined whether the octopus can also turn its eyes upwards and downwards, and if so, to what degree.
Scientists conclude Octopus DNA is out of this world
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A new study has led researchers to conclude that Octopuses (NOT Octopi) have Alien DNA. Their genome shows a never-before-seen level of complexity with a staggering 33,000 protein-coding genes identified, more than in a human being.
The oceans of our planet hide countless mysteries that could perhaps help answer numerous mysteries of life itself. During the last couple of decades, marine biologists have made small but steady progress towards a deeper understanding of nature and life.
A group of researchers decided to do some science and chose the cephalopods in order to try and break down their DNA code, hoping to understand them better.
The octopus, squid, and cuttlefish are integrated into the coleoid sub-class of the molluscs. They have an evolutionary history that goes back over 500 million years, a period long before plants moved onto land. These creatures inhabit nearly every single ocean at almost any depth.
They are mainly characterized by a vast range of incredible morphological wrinkles: camera-like eyes, really flexible bodies, and ‘sophisticated’ chameleonic response. All of this is ruled by the larger nervous system found among invertebrates, which makes these beings the rulers of the oceans.
They possess highly developed brains and are considered as the most intelligent invertebrate demonstrating elaborate problem-solving behaviours. And ss if it wasn’t freaky enough for octopuses to open up jam jars, scientists have just concluded that these aquatic creatures are even more mysterious.
Thanks to the first-ever full genome sequence, researchers have found that octopuses (NOT Octopi) are in fact entirely different from any other animals on our planet. Their genome shows a never-before-seen level of complexity with a staggering 33,000 protein-coding genes identified, more than in a human being.
US researcher Dr. Clifton Ragsdale, from the University of Chicago, said: The octopus appears to be utterly different from all other animals, even other molluscs, with its eight prehensile arms, its large brain, and its clever problem-solving abilities.
“The late British zoologist Martin Wells said the octopus is an alien. In this sense, then, our paper describes the first sequenced genome from an alien.”
One of the mains reasons why researchers decided to investigate the molecular basis of cephalopod brain, was its ability to adapt instantly its neural network properties which result in a great impact in memory and learning capacity. These specific capabilities offer an explanation within the genome that incorporates biological mechanisms that allow tissues to rapidly change proteins in order to alter their function.
According to researchers from the University of Chicago, the octopus genome is enriched in transposons, commonly referred to as “jumping genes,” which can rearrange themselves on the genome. Even though their role in octopuses is unclear, researchers found elevated transposon expression in neural tissues. Transposons are known to have the ability to affect the regulation of gene expression and are believed to play major roles in shaping genome structure. (Source)
“With a few notable exceptions, the octopus basically has a typical invertebrate genome that’s just been completely rearranged, like it’s been put into a blender and mixed,” said Caroline Albertin, co-lead author and graduate student in Organismal Biology and Anatomy at the University of Chicago. “This leads to genes being placed in new genomic environments with different regulatory elements, and was an entirely unexpected finding.” (Source)
Octopuses have an alien genetic baggage. The scientific report mainly concluded that Octopuses share ‘Alien’ genes.This has been a ground shaking claim in the scientific community which caused an upheaval among marine biologists who seemed to be shocked and intrigued at the same time.
It turns out that apparently, we’ve had under our nose a link to humanity’s mysteries, and many of life’s greatest enigmas can be solved if we only decide to pay more attention to our ocean and everything inside of it.
This Is Why Mother Octopuses Grimly Starve Themselves to Death
Clever and strange, octopuses are fascinating creatures with incredible problem-solving skills and breathtaking camouflage. But overall, they are short-lived, typically around for just one to two years.
That's because they're semelparous, which means they reproduce just once before they die. With female octopuses, once she's laid her eggs, that's it.
In fact, the mother even stops feeding - she'll stay and watch over her eggs until they hatch, slowly starving to death. In captivity, towards the end, sometimes she'll tear off her own skin, and eat the tips of her own tentacles.
Now, scientists have figured figured out why this grim scenario happens. It has to do with the optic gland between the octopus's eyes a gland similar to the pituitary gland in humans.
In 1977, researchers removed this gland and found that the octopus' mothering instincts disappeared. She abandoned her eggs, started feeding again, and went on to live a much longer life.
The maturation of the reproductive organs appears to be driven by secretions from the optic gland. These same secretions, it seems, inactivate the digestive and salivary glands, which leads to the octopus starving to death.
In new research, neurobiologists from the University of Chicago used genetic sequencing tools to describe the precise molecular signals produced by the optic gland of a female California two-spot octopus (Octopus bimaculoides) after reproducing.
They also described four distinct phases of maternal behaviour that they were able to link to these signals, explaining how the optic gland drives her death.
"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," said neurobiologist Z. Yan Wang.
"These behaviours 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 behaviours, which to me is the entire purpose of studying neuroscience."
The first phase is a mature, non-mated female, who is active and an agile and aggressive hunter, spending a lot of time out of her dens.
In the second phase, just after brooding, she will watch over her eggs, stroking them and blowing water over the clutch. She won't actively go out and hunt, but she may snare the occasional unlucky crab that ventures too close. This lasts around 3 to 4 days.
In the third phase, she stops eating entirely, growing more listless. This lasts 8 to 10 days.
Finally, in the fourth phase, she grows agitated. The researchers observed the octopuses slamming themselves against their tanks, grooming themselves ragged, tangling their tentacles and growing pale and emaciated, before dying shortly after the eggs had hatched.
The researchers collected the optic glands from octopuses in each of these four stages, and sequenced the RNA to find out exactly what was occurring.
Before mating, the octopuses produced high levels of neuropeptides, small protein-like molecules that have been linked to feeding behaviour in many animals. After mating, neuropeptide production plummeted.
After mating, the octopuses showed an uptick in the production of catecholamines, steroids that regulate cholesterol metabolism and insulin-like factors - the first time the optic gland has been linked to a function that doesn't have something to do with reproduction.
The finding suggests that the optic gland doesn't produce just a single hormone to regulate reproduction, but uses multiple signalling pathways, possibly to keep the mother octopus watching over her precious eggs.
How these pathways occur is still a puzzle to be unravelled - whether the neurotransmitters that kick in after mating target reproductive tissues that promote maternal instincts, or shut down the digestive functions to keep her closer to her eggs is unknown.
"Before when we only knew about the optic gland, it felt like watching the trailer to a movie," Wang said. "You get the gist of what's going on, but now we're beginning to learn about the main characters, what their roles are and a little bit more about the backstory."
What's also is unknown is why male octopuses tend to die shortly after mating as well, even though they don't have the same parental obligation to care for the eggs. So, there are still plenty of mysteries to be unravelled when it comes to our tentacled friends.
The team has published their paper in the Journal of Experimental Biology.
The grim, final days of a mother octopus
Octopuses are the undisputed darlings of the science internet, and for good reason. They're incredibly intelligent problem-solvers and devious escape artists with large, complex nervous systems. They have near-magical abilities to change colors, skin textures and shapes instantaneously, and they can regenerate missing arms at will.
But the final days of a female octopus after it reproduces are quite grim, at least to human eyes. Octopuses are semelparous animals, which means they reproduce once and then they die. After a female octopus lays a clutch of eggs, she quits eating and wastes away by the time the eggs hatch, she dies. In the later stages, some females in captivity even seem to intentionally speed along the death spiral, banging into the sides of the tank, tearing off pieces of skin or eating the tips of their own tentacles. (If you're wondering, the males don't get off any easier. Females often kill and eat their mates if not, they die a few months later, too).
In 1977, Brandeis University psychologist Jerome Wodinsky showed that if he removed the optic gland from female Caribbean two-spot octopuses (Octopus hummelincki), something interesting happened. The optic gland is similar to the pituitary gland of most land animals, so-called because it sits between the eyes. Without them, the female octopuses abandoned their eggs, resumed feeding, and some even mated again. At the time, Wodinsky and other cephalopod biologists concluded that the optic gland must secrete some kind of "self-destruct" hormone, but just what it was or how it worked was unclear.
Now, a new study by neurobiologists at the University of Chicago uses modern genetic sequencing tools to describe several distinct molecular signals produced by the optic gland after a female octopus reproduces. The study, published in the Journal of Experimental Biology, also details four separate phases of maternal behavior and links them to these signals, suggesting how the optic gland controls a mother octopus' demise.
"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," said Z. Yan Wang, a graduate student in neurobiology at UChicago who led the research study.
"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," she said.
Mapping the death spiral
In 2015, Clifton Ragsdale, PhD, professor of neurobiology at UChicago, and his team sequenced the genome of the California two-spot octopus (Octopus bimaculoides), the first cephalopod ever to be fully sequenced. Wang was a part of that research team and has continued building on that foundation for her PhD thesis.
In the new study, she used the same California two-spot octopuses to study their odd maternal behaviors. Mature, non-mated females are active predators who spend a lot of time outside their dens and quickly pounce on prey-like fiddler crabs. In the first stage of brooding though, mated females sit with their eggs like a deep-sea hen, stroking them and blowing water over the clutch. For the first three or four days they continue feeding but rarely leave their eggs, snatching the odd unlucky crab only if it happens to get too close.
After four days or so, they stop eating completely. This stage of brooding can last eight to ten more days until they hit the final phase of rapid decline, when things get really ugly. The females become listless, spending more time away from their eggs or slamming themselves against the corners of the tank. They start grooming themselves excessively, running their arms over their mantles until they became a tangled mess. Their skin pales and they lose muscle tone, even beyond what you would expect to see in a starving octopus.
Wang, who has made pets out of some of the octopuses in the lab, said, "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."
Reading the script from the optic gland
Wang collected the optic glands from octopuses at each phase and sequenced the RNA transcriptome of each. RNA carries instructions from DNA about how to produce proteins, so sequencing it is a good way to understand the activity of genes and what's going on inside cells at a given time.
During the non-mated phase when females were actively hunting and eating, they produced high levels of neuropeptides, or small protein molecules used by neurons to communicate with each other that have been linked to feeding behavior in many animals. After mating, these neuropeptides dropped off precipitously.
As the animals began to fast and decline, there was more activity in genes that produce neurotransmitters called catecholamines, steroids that metabolize cholesterol, and insulin-like factors. Wang said finding activity related to metabolism was surprising because it's the first time the optic gland has been linked to something other than reproduction.
Just how these molecular and signaling changes cause the different behavioral changes is unclear though. Females in the early stage of brooding continued to eat but didn't actively seek out food. This could mean that the neuropeptides affect the amount of energy the octopus expends to find prey. Certain muscles may begin to deteriorate so the octopus physically can't hunt or digest food. The increased steroid and insulin production could be targeting reproductive tissues that promote maternal behavior, or they could be directing energy away from digestion and feeding.
"Before when we only knew about the optic gland, it felt like watching the trailer to a movie," Wang said. "You get the gist of what's going on, but now we're beginning to learn about the main characters, what their roles are and a little bit more about the backstory."
Death in the octopus world
The scientific jury is still out as to why these clever, resourceful creatures meet such an ignominious end, but there are several theories. Octopuses are serious cannibals, so a biologically programmed death spiral may be a way to keep mothers from eating their young.
They can also grow pretty much indefinitely, so eliminating hungry adults keeps the octopus ecosystem from being dominated by a few massive, cranky, octopus versions of Baby Boomers. But maybe it's not fair to impose our human perspective on the cephalopod world.
"It's very strange to see as humans because we reproduce more than once and live way past our reproductive age," Wang said. "But if the whole purpose of living is to pass along your genes, maybe it's not so dark."