The Hearts Inside

It’s a science fiction trope… A few soldiers walking down a dimly-lit spaceship, weapons drawn, as unsettling splatters of blood cover the walls—only some of it red. The blood that circulates in our bodies has a cultural significance that is difficult to overstate, its deep scarlet hue being used to imply everything from rage to romance to power. Perhaps this is why differently colored blood is used to show that the very essence of alien beings is completely foreign to the human experience. What you may not know, however, is that these aliens walk—and swim—among us.

Photo credit    Leslie Sherlin

Photo credit Leslie Sherlin

Many invertebrate animals have blue blood, and octopuses are no exception. Our blood is red due to the protein hemoglobin, more specifically the iron contained within hemoglobin, which binds to oxygen and carries it throughout our body to each of our cells. The octopus blue blood, on the other hand, uses copper instead of iron to carry oxygen. This comes with the added benefit of remaining functional in a wide variety of temperatures, which is particularly useful for ectothermic organisms. This is part of why octopuses have been found everywhere from the Caribbean to the Arctic circle. Hemocyanin does not, however, come without its costs. For one, it is highly sensitive to changes in pH. This means that if octopuses do not adapt quickly, they may be negatively impacted by the acidification of our oceans from the mass emission of carbon dioxide. In addition, hemocyanin is not as efficient as hemoglobin.

This, along with their sophisticated brain, astronomical growth rate, and relatively active lifestyle, causes octopuses to have a massive metabolism, and consequently, require a lot of oxygen. In fact, while most other mollusks, as well as fish, require a 3% oxygen saturation in their blood, octopuses demand a hefty 11%. This has also influenced their evolution. To compensate for this gluttonous oxygen demand, their cephalopodan ancestors developed a closed circulatory system, while other mollusks maintained an open system. In other words, the blood of an octopus travels through capillaries to perfuse its tissues while snail blood simply mixes with the extracellular fluid. If this sounds too familiar, don’t worry, for they have not one, nor two, but THREE hearts. One brachial heart is paired with each gill and a third systemic heart pumps the blood throughout the rest of the body. As strange as this may be, we vertebrates had to optimize blood flow to keep pace with our energy demands as well. While we divided our hearts into chambers, keeping the oxygen-rich blood on the right side for maximum concentration, octopuses and their relatives developed entire separate organs for this same purpose.

The blue blood of an octopus, along with its bizarre cardial anatomy, may evoke images of extra-terrestrials, and while this may be technically inaccurate, it is perhaps not far from the truth. After all, you would expect any organism that diverged from our lineage hundreds of millions of years ago to be drastically different from humans. But even stranger is that, despite all their differences, they still seem so eerily similar to ourselves.

Further Reading:

https://cardiovasculardreamteam.weebly.com/octopus.html

https://sciencing.com/an-octopus-breathe-4566479.html

http://www.jstor.org/stable/30158158

https://ocean.si.edu/ocean-life/invertebrates/cephalopods

https://www.smithsonianmag.com/science-nature/ten-curious-facts-about-octopuses-7625828/

A Blind Rainbow - What Do Octopuses See, Anyway?

Few things are more captivating than watching an octopus moving along the seafloor constantly changing its own appearance to match its environment. What biological mechanisms could possibly make those brilliant colors flash so quickly?  This mystery becomes even more compelling when we know that octopuses cannot see the colors themselves!

Photo by    Vlad Tchompalov

The human eye possesses two types of specialized cells in the retina: rods and cones. Rod cells are the most sensitive and are specifically adapted to operate in low-level light. The downside of this is that they cannot differentiate between different wavelengths of light—that is, they detect only “grayscale” images. This is compensated for by the cone cells, which detect only particular wavelengths, thus enabling color vision. An octopus eye, however, lacks these cone cells. But wait—then their color changing should be impossible, right? Surely, they must have some way to detect colored light! This is a question we still cannot answer definitively, though there are a few guesses. One is that the eye lens accomplishes this for them through refraction, just like a rainbow. Rainbows are formed by raindrops in the air on a sunny day, which causes the light to bend differently as it passes through, separating it into the brilliant bands we see streak across the sky. It would be as if this rainbow were cast directly onto the retina, enabling octopuses to see colors, and by extension, construct equally dazzling displays on their own skin.

Another possibility is that while their eyes are truly colorblind, perhaps the skin itself can see. This actually isn’t as crazy as it sounds; even jellyfish can detect some light (though this is not “sight” as we think of it, because they do not create an image). Some researchers have found that the chromatophores, the color changing cells, of an octopus’s skin actually do respond to some wavelengths of light due to the presence of a protein called opsin. This opsin is the same protein that detects the light in our eyes. So maybe the octopus isn’t even aware of the show it is putting on, or the beauty it possesses. Like Beethoven near the end of his life, the octopuses themselves may be the only ones unable to appreciate their own artistry. But hey, at least it keeps the eels away.

Further Reading:

https://www.theguardian.com/science/neurophilosophy/2015/may/20/octopus-skin-contains-light-sensors

http://www.ucmp.berkeley.edu/cnidaria/scyphozoamm.html

http://news.berkeley.edu/2016/07/05/weird-pupils-let-octopuses-see-their-colorful-gardens/

Beauty Skin Deep - How Do Octopuses Change Color?

After watching octopuses rapidly change their color several times each second, everyone has the same question: how do they do it? How dynamic is their skin? Can I get some octo skin for myself? Okay, that may be more than one question, but the amazement and wonder regarding their pixelated displays is surely genuine. As far as how they do it, there are actually a few different layers of their skin that all come together to make them even more incredible than we can sense.

SSSeas Octopus Skin Sherlin 03.jpg

Octopus Skin

Photo credit Leslie Sherlin

The most basal layer of octopus skin includes leucophores, which reflect any wavelength of light. This basically means that they are white, so we’ll skip to the topmost layer, which is responsible for all of the brilliance we actually see: the chromatophores. Essentially, these cells are sacks of pigment attached to some muscles spiking outward like the spokes of a wheel. These muscles control the size of that sack, making them wide and bold or shrink away to a minuscule dot. They can change their color at the speed of thought, which explains the lightning speed with which they disappear into coral or a rocky background. These pigments are generally red, yellow and brown, and provide an assortment of warm, dull colors to their repertoire.

Photo credit  Leslie Sherlin

Photo credit Leslie Sherlin

But wait, you may be thinking, I’ve seen blue rings on an octopus before! This chic hue comes from a far more interesting set of cells, the iridophores. These, like the leucophores, reflect light very well, but only at particular wavelengths, including silvers, golds, and greens. The wavelength they reflect also depends on the angle of the light, meaning that the octopus may be a different color depending on where the viewer, or camera, happens to be. These can also be altered or adjusted, but they are under hormonal control, and are thus much slower.

Further Reading:

https://www.nature.com/scitable/topicpage/cephalopod-camouflage-cells-and-organs-of-the-144048968

http://www.thecephalopodpage.org/cephschool/HowCephalopodsChangeColor.pdf

An Intelligence Divided

How do we assess the intelligence of other species? One way is to search for certain skills and abilities, such as the use of a tool or the modification of an environment. However, the determination of whether an animal is considered proficient at these tasks is often subjective.

And, we need to acknowledge the anthropocentric selection of the behaviors that we consider to be signs of intelligence. Another measure commonly used is brain-to-body mass ratio, though this measure has issues as well— it would predict some rodents and birds to be more intelligent than humans, and few of us would like to believe this assessment. We can adjust depending on the specific animal groups we are trying to evaluate, but it’s still problematic.

Photo credit    Janayara Machado

Photo credit Janayara Machado

For instance, octopuses defy the norm and reshape how we view intelligence in the natural world. This is not to say that octopuses lack an impressive brain—just the opposite. Overall, they boast 500 million neurons. For comparison, common garden snails, a molluscan relative, have only 10,000, and humanity’s best friend the dog just barely beats them at 600 million. Their actual brain, however, has just 50 million neurons, while much of their leftover processing power is distributed throughout their arms, which contain more than a whopping 300 million! So, what all does this mean?

We have come to find out that although octopuses do have a central brain, they do not have a central mind, per se. In fact, when an octopus arm is detached from its body, it will still hunt for food…no, really. Even though the arm is no longer attached to a brain, it will continue responding to stimuli, recoil from pain, and even guide food to where its mouth used to be. Perhaps this is how an octopus knows how to control not only its arms and their complex movements, but also its skin color and all the other complex behaviors their otherworldly anatomy permits.

This division of intelligence has been proposed by many as a means of furthering AI (artificial intelligence)— something that humans may ultimately prove too single-minded to understand.

Further Reading:

https://www.scientificamerican.com/article/does-size-matter-for-brains/

https://www.cell.com/current-biology/pdf/S0960-9822(08)00966-4.pdf

https://blogs.scientificamerican.com/octopus-chronicles/even-severed-octopus-arms-have-smart-moves/

https://www.smithsonianmag.com/smart-news/severed-octopus-arms-have-a-mind-of-their-own-2403303/

http://www.digitaljournal.com/article/357271

https://www.seeker.com/octopus-inspires-ai-robots-on-a-mission-1771111049.html

A Venomous Bite - Are Octopuses Poisonous?

Even regarding octopuses, the old adage holds true: if it’s in Australia, it can kill you. Specifically, the blue-ringed octopus packs enough venom in its bite to take down a person in minutes. What is the dastardly appearance of such a deadly creature? A tiny animal no more than 4 inches long, with a pale, yellow coloring and iridescent rings of blue.

The major component of their defensive venom is a chemical known as tetrodotoxin, also found in some fish, amphibians, and shellfish. Tetrodotoxin binds to certain voltage-gated sodium channels, inhibiting their function. Because the action potentials of the nervous system are themselves generated and propagated by the movement of these ions, this is an extremely potent neurotoxin. Its victims may experience paralysis, nausea, numbness, and convulsions until the respiratory system completely shuts down. And if that isn’t bad enough, their saliva delivers it along with histamine, octopamine, hyaluronidase, and a slew of other fun chemicals to make an encounter with this octopus particularly memorable.

While the blue-ringed beauties are the only octopuses with a bite lethal to humans, all come with a venom in their saliva, though it is mainly used for predatory purposes, and you may have noticed evidence of this yourself. If you walk down a beach and notice a shell with a neat hole in it, that is likely due to the radula, or rasping tongue, of a mollusk, octopuses being included in that group. They then spit their venom into the prey to paralyze it, allowing them to enjoy an easy meal. So, all octopuses have a certain amount of dark alchemy within them, but assuming you aren’t a crab, you don’t have much to worry about from the curious, squishy aliens of the deep.

Further Reading:

https://www.barrierreefaustralia.com/info/reef-dangers/blue-ringed-octopus/

http://marinebio.org/species.asp?id=403

https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/blue-ringed-octopus

https://www.cdc.gov/niosh/ershdb/emergencyresponsecard_29750019.html

https://pubchem.ncbi.nlm.nih.gov/compound/4490623#section=Toxicity

http://www.molluscs.at/cephalopoda/index.html?/cephalopoda/main.html