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Octopuses, and Maybe Squid, Can Sense Light With Their Skin

Octopuses, squid, and cuttlefish, the animals collectively known as cephalopods, are capable of the most incredible feats of camouflage. At a whim, they can change the colour, pattern, and texture of their skins to blend into the background, baffle their prey, or communicate with each other.

As if that wasn’t amazing enough, Lydia Mäthger and Roger Hanlon recently discovered that the common cuttlefish has light-sensitive proteins called opsins all over its skin. Opsins are the engines of sight. Even though animal eyes come in a wondrous variety of shapes and structures, all of them use opsins of one kind or another. The discovery of these proteins in cuttlefish skin suggested that these creatures might be able to sense light over their entire surface, giving them a kind of distributed “sight”.

It was a tantalising suggestion, but far from a definitive one. Opsins are used in many other contexts, such as sensing the time of day, which still involve detecting light but have nothing to do with seeing images. To work out what exactly opsins are doing in cephalopod skin, the team needed more evidence.

For example, when opsins are struck by light, they change shape. This triggers a Rube Goldberg-esque chain of further changes in other proteins, which culminates in an electrical signal travelling through a nerve towards the brain. That’s the essence of vision. It’s what happens in a cephalopod’s eye. Does it also happen in their skin?

That’s exactly what Alexandra Kingston from the University of Maryland, Baltimore County decided to find out. Working with Hanlon and vision expert Tom Cronin, Kingston studied the skins of the longfin inshore squid, the common cuttlefish, and the broadclub cuttlefish, looking for proteins that act downstream of opsin.

She found them. Several of them are present in the animals’ skin, and only in the chromatophores—the cells that are primarily responsible for their shifting patterns. Each chromatophore is an elastic sac of pigment, surrounded by a starburst of muscles. If the muscles relax, the sac contracts into a small dot that’s hard to see. When the muscles contract, they yank the sac into a wide disc, revealing the colour it contains. Kingston showed that these living pixels contain the same Rube Goldberg set-up that exists in their owners’ eyes.

Her team couldn’t, however, show that the chromatophores actually respond to light. “All the machinery is there for them to be light-sensitive but we can’t prove that. It’s been very frustrating,” says Cronin. The chromatophores might be detecting local light levels to prime them for either expansion or contraction. They could communicate with each other so that small clumps of chromatophores react to light as a unit. Or they could send signals directly to the brain to provide their owners with more information about light levels in their environment. These possibilities could all be right or wrong; no one knows.

“We don’t know if they contribute to camouflage or are just general light sensors for circadian cycling or are driving hormonal changes. They have a job to do but we don’t know what it is,” says Cronin. “That’s biology!” he adds, resignedly.

Cuttlefish. Credit:  Peter Hellberg
Cuttlefish. Credit: Peter Hellberg

Meanwhile, Desmond Ramirez and Todd Oakley from the University of California, Santa Barbara had better luck with a different cephalopod—the California two-spot octopus. When the duo shone bright light onto isolated patches of skin, they found that the chromatophores would dramatically expand. They called this light-activated chromatophore expansion, or LACE.

Ramirez and Oakley showed that the octopus’s skin also contains opsin, but not in the chromatophores. Instead, its opsins reside in small hair-like structures called cilia. People used to think that the octopus used these cilia as organs of touch; they still could be, but they might also detect light too. And echoing Cronin, Oakley says, “We don’t know yet how this is used, or indeed if it is used, in the living animal.”

ColorLACE(1)Neither study is definitive, but they certainly complement each other. They strengthen the case that these animals really are detecting light with their skins, independently of their brains and eyes.

They also serve as useful reminders that cephalopods are a diverse group of very different animals, with different branches separated by over 280 million years of evolution. It shouldn’t be surprising that octopus skin readily responds to light, but squid and cuttlefish skin doesn’t seem to. Or that, in octopus skin, opsins are found in cilia, while in squid and cuttlefish, they live in chromatophores.

They behave differently, too. “Cuttlefish and squid do seem to display to each other more than octopuses,” says Cronin. “Octopuses do pattern dramatically in response to environmental changes, but we don’t know of displays in octopuses designed for other octopuses.” Perhaps each species uses its skin opsins for different tasks.

Reference: Ramirez & Oakley. 2015. Eye-independent, light-activated chromatophore expansion (LACE) and expression of phototransduction genes in the skin of Octopus bimaculoides. Journal of Experimental Biology http://dx.doi.org/10.1242/jeb.110908

Kingston, Kuzirian, Hanlon & Cronin. 2015. Visual phototransduction components in cephalopod

chromatophores suggest dermal photoreception. Journal of Experimental Biology. http://dx.doi.org/10.1242/jeb.117945

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The Squid Whisperer

It was a delight to profile the wonderful Margaret McFall-Ngai for Nature. She has done some great work on partnerships between a squid and its luminous bacterium, and she’s a powerful force in the world of animal-microbe partnerships. She’s also much-loved in the field; I have never had so many sources practically falling over themselves to sing someone’s praises. McFall-Ngai’s work will feature in my upcoming book, so consider this a little taster.

The aquarium looks empty, but there is something in it. A pair of eyes stick out from the sandy floor, and their owner is easily scooped up into a glass bowl. At first, the creature looks like a hazelnut truffle — small, round and covered in tiny flecks. But with a gentle shake, the flecks of sand fall off to reveal a female Hawaiian bobtail squid (Euprymna scolopes), about the size of a thumb. As she jets furiously around the bowl, discs of pigment bloom and fade over her skin like a living pointillist painting.

There are no other animals in the bowl, but the squid is not alone. Its undersides contain a two-chambered light organ that is full of glowing bacteria called Vibrio fischeri. In the wild, their luminescence is thought to match the moonlight welling down from above and cancel out the squid’s shadow, hiding the animal from predators. From below, the squid is invisible. From above, it is adorable. “They’re just so beautiful,” says Margaret McFall-Ngai, a zoologist at the University of Wisconsin–Madison. “They’re phenomenal lab animals.”

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How Big Are The Biggest Squid, Whales, Sharks, Jellyfish?

A few years ago, Carl Zimmer and I ran a workshop on science writing, where we talked, among other things, about explaining science without talking down to your audience. It apparently left an impression on Craig McClain, a marine biologist and blogger who was in the audience. “I made a comment about how I always wanted to write a post on how giant squid sizes are bullsh*t,” he recalls,” but that those always come off as an arrogant scientist telling the world that it’s wrong. And you said: You should write it, but you just need to find the right tone. That kicked me off.”

Rather than an angry blog post, McClain decided to put together a scientific paper that would accurately answer a simple yet slippery question: How big do the biggest animals in the ocean get?

The oceans are home to giants: blue whales and great white sharks; giant squids and giant clams; elephant seals and Japanese spider crabs. These creatures have no trouble capturing the public imagination, but scientists often have trouble capturing them. Many are rare, elusive, or live in inaccessible parts of the sea. Some are only measured when they wash ashore, after dry land distends or deflates their bodies. Some are so big that they are just plain hard to measure. And so, oceans are also home to exaggeration.

Take the giant squid. Umpteen media report claim that this nigh-mythic animal can grow up to 60 feet (18 metres) in length. That’s absurd, McClain thought. The vast majority are less than half that length. Many individuals are measured when they wash ashore, after decomposition loosens their muscles and eager humans stretch their tentacles. One size estimate even came from someone counting his paces next to a beached squid! Shoddy data had been unleashed upon the kraken.

McClain, together with Meghan Balk from the University of New Mexico, went after better sources. They recruited five keen undergraduate students and large team of colleagues, who divided a list of target species between them. They trawled the scientific literature for measurements. They combed through books, newsletters, and newspapers. They asked colleagues at museums to measure specimens in their collections. They contacted networks that rescue stranded turtles. They reeled in eBay records to find the measurements of giant clams and snail shells. And together, they found the best possible estimates for the maximum sizes of 25 ocean giants.

For some species, widely quoted figures were outrageously wrong. The largest verifiable giant squid was 12 metres long—giant, sure, but a damn sight smaller than 18 metres. The biggest known walrus weighed 1,883 kilograms, a far cry from the 2,500 kilogram titan that a hunter supposedly shot, and clearly embellished.

For some species, estimates were outdated—giant clam sizes all date to the 60s and 70s. For others, like the lion’s mane jellyfish and Japanese spider crab, the team found that accurate data just doesn’t exist.

And “some animals may just not be getting as big as they used to get,” says McClain. In 1885, fishermen in the Aleutian Islands caught a Giant Pacific octopus that was 9.8 metres from one arm tip to the next. “The two octopus experts who were with me on this paper say that they just don’t get that big any more,” says McClain. “It could be pollution or climate change.”

Hype and decline aside, the stats from the paper still tell of oceans that are full of impressive leviathans. There are giant barrel sponges, whose bodies are just two layers of cells sandwiching a jelly filling, but can nonetheless grow to 2.5 metres wide. There are 2-metre-wide Nomura’s jellyfish that can weigh 200 kilograms. In the depths, 3-metre-long giant tube worms thrive near hot, belching, volcanically heated vents, and giant isopods—a kind of undersea woodlouse on steroids—can reach 50 centimetres. Seven treacherous metres exist between the tip of a great white shark’s toothy snout and the end of its powerful tail.

The largest mammal, the blue whale, grows up to 33 metres long, and can swallow half a million calories in one mouthful. The longest fish—the star-backed whale shark—gets to 18.8 metres. The longest bony fish—the bizarre, serpentine oarfish—can reach 8 metres. The heaviest bony fish—the ocean sunfish, which looks like the decapitated head of a much larger fish—grows to just 3.3 metres long but weighs up to 2,300 kilograms. That’s much heavier than the biggest turtle (leatherback, 650 kg), a little heavier than the biggest walrus (1,883 kg), and not a patch on the heaviest seal (Southern elephant seal, 5,000 kg).

These measurements are all as accurate as possible; finding them often involved a labyrinth of references and phone calls. For the Australian trumpet—a beachball-sized monster of a snail—McClain found an issue of Hawaiian Shell News, in which a collector named Don Pisor holds up an enormous and supposedly 90-cm shell. But McClain also found a copy of the Registry of World Record Size Shells, which said that the record-holder was just 72 centimetres long. It was also attributed to Don Pisor. Were these the same specimens? Was this guy a charlatan? Or just phenomenally good at catching escargods? There was only one thing to do: McClain tracked down Pisor and asked him. It was just one specimen, he said, and he donated it to the Houston Museum of Natural Science. McClain called the museum. 72 centimetres, they said. Another data point for the list.

In a few cases, the team discovered new things about the giants. Andrew Thaler, who collected the data on giant isopods suddenly realised that males were, on average, much bigger than females. “That’s not something either of us knew before and both of us know everything there is to know about giant isopods,” says McClain.

And for several animals, the team managed to plot out the distribution of their sizes, rather than just the maximum. Scientifically, that’s more useful. People love to know how big animals can get, but that tells us very little about their typical lives. The biggest known giant squid was 12 metres long, but their average length is 7.3 metres, and most individuals are shorter than 9.2. Its archenemy, the sperm whale, has a recorded maximum size of 24 metres, but 95 percent of these whales are shorter than 15 metres.

As McClain—himself a bear of a man at 6’ 2”—points out, “individuals may reach these extraordinary large sizes through developmental or genetic defects.” The tallest human ever, Robert Wadlow, was 8 feet and 11 inches in height; he also needed leg braces to walk and died at 21 from an infection aggravated by an autoimmune disease. The tallest woman, Zeng Jillian, reached her lofty 8 feet and 1 inch because of a tumour in her pituitary gland; she died at 17. We are fascinated by extremes, but life mostly plays out in the middle.

Reference: McClain, Balk, Benfield, Branch, Chen, Cosgrove, Dove, Helm, Hochberg, Gaskins, Lee, Marshall, McMurray, Schanche, Stone & Thaler. 2015. Sizing ocean giants: patterns of intraspecific size variation in marine megafauna. PeerJ http://dx.doi.org/10.7717/peerj.715

More: The students created a website—Story of Size—where they wrote about their work.

Spineless Giants Track Oceanic Revolutions

We’re fascinated by superlative size. That’s why humungous dinosaurs regularly make headlines, and Carboniferous arthropods – dragonflies and millipedes that reached B-movie sizes by dint of higher atmospheric oxygen – are paleo-documentary regulars. And beyond their size, we’re transfixed by why and how such giants could evolve. What’s strange, then, is that we haven’t paid more attention to the giant marine invertebrates of the prehistoric past.

Today’s giant and colossal squids were hardly the first invertebrate giants to inhabit the seas. Squishy and shelly critters with sizes over a foot and a half long have evolved multiple times during the last 500 million years and are well-known among paleontologists who specialize in spineless species. Endoceras giganteum, a 451 million year old cephalopod that lived inside an elonged cone of a shell, could get to be about 15 feet long, and there are rumors of lost specimens 30 feet in length. The 404 million year old sea scorpion Jaekelopterus rhenaniae has been estimated to be over eight feet long, and the 465 million year old trilobite Hungioides stretched nearly three feet long. And that’s just a few of prehistory’s immense invertebrates.


The shell of an immense Endoceras. From Klug et al., 2014.
The shell of an immense Endoceras. From Klug et al., 2014.

But is there any pattern to the origin of these tentacled and joint-legged giants? That’s the question behind a newly-published study by Universität Zürich paleontologist Christian Klug and colleagues in the journal Lethaia. Within a window of 500 to 300 million years ago, Klug and coauthors looked to see if the occurrence of giant cephalopods and arthropods in space and time corresponded to changes in oxygen levels, temperature, and sea level.

There was no simple connection between the environmental factors – all implicated as possible triggers for gigantism – and large body size among the marine invertebrates. Instead, the superlative species seemed to cluster around two times when marine life flourished.

Within their 200 million year window, Klug and colleagues found, the largest shell-covered cephalopods evolved about 475 million years ago. The largest trilobites weren’t very far behind, at 468-460 million years old, and another group of archaic arthropods – the weird anomalocaridids – counted their largest members in the 488-472 million year range. All three groups independently evolved huge size within a 28 million year window that coincides with the Great Ordovician Biodiversification Event – an evolutionary pulse that not only spun off many new species, but also allowed new, complex marine ecosystems to evolve.

Many of the other species in the study – including large cephalopods, trilobites, and sea scorpions – cluster around another, narrower window. All of these different groups again generated giant species between 400 and 383 million years ago during an event called the Devonian Marine Nekton Revolution. In brief, seafloor and deep water habitats were so saturated with species that competition drove the evolution of more animals capable of living suspended within the water column.

Huge, cone-shelled cephalopods and massive trilobites didn’t evolve because of simple causes such as an abundance of oceanic oxygen or dips in ocean temperature. Giants evolved in cool and warm seas at high and low sea levels and at various oxygen concentrations. Instead, remarkable body size among the marine invertebrates appears to be tied to major diversification events. Whatever allowed the group as a whole to flourish, Klug and colleagues point out, is what gave rise to giants.

Maps showing the distribution of marine invertebrate giants through time, with the oldest at the bottom. The pink swaths are the limits of tropical seas. From Klug et al., 2014.
Maps showing the distribution of marine invertebrate giants through time, with the oldest at the bottom. The pink swaths are the limits of tropical seas. From Klug et al., 2014.

But environmental shifts may explain a different part of the evolutionary picture.

Between 500 and 370 million years ago, most of the giants lived at high latitudes, closer to the poles. But starting at 370 million years ago, their occurrences creep down the latitudes towards the equator. And it was during this time that glaciers were forming in the southern hemisphere, the global sea level sank, temperatures dropped, and oxygen levels rose more than 20%, creating cooler, nutrient-rich seas. Perhaps these cooler, more productive seas created new constraints for where the biggest invertebrates could live.

This could be a coincidence. Klug and coauthors point out that sampling bias – where fossils are and can be collected – might influence this pattern, and note that perhaps continental shifts created rich, productive shelf environments that altered where giant species were likely to evolve. But the fact that all the groups investigated in the study – belonging to distinct lineages different in anatomy and physiology – followed this pattern suggests there’s some as-yet-unknown cause for the global shift. Paleontologists can pick out the biggest of the big, but why marine giants emerged where they did requires the continued imagination and investigation of long-lost seas.


Klug, C., de Baets, K., Kröger, B., Bell, M., Korn, D., Payne, J. 2014. Normal giants? Temporal and latitudinal shifts of Palaeozoic marine invertebrate gigantism and global change. Lethaia. doi: 10.1111/let.12104.

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Adaptive Colour-Changing Sheet Inspired By Octopus Skin

The most amazing skins in the world can be found in the sea, stretched over the bodies of octopuses, squid and cuttlefish. These animals, collectively known as cephalopods, can change the colour, shape and texture of their skin at a whim—just watch the ‘rock’ in the video above suddenly reveal its true nature. Their camouflage is also adaptive. Unlike, say, a stick insect or stonefish, which are limited to one disguise, an octopus’s shifting skin allows it to mimic a multitude of backgrounds. It sees, it becomes.

No man-made technology comes close. But one, at least, is nudging in the right direction.

A team of scientists led by Cunjiang Yu at the University of Houston and John Rogers at the University of Illinois at Urbana–Champaign have developed a flexible pixellated sheet that can detect light falling upon it and change its pattern to match. So far, its large pixels can change from black to white and back again. It’s a far cry from an octopus’s skin, but it does share some of the same qualities. For example, it changes colour automatically and relatively quickly—not cephalopod-quick, but within a second or so.

“This is by no means a deployable camouflage system but it’s a pretty good starting point,” says Rogers. Eventually, his team are working towards adaptive sheets that can wrap around solid objects and alter their appearance. These could be used to make military vehicles that automatically camouflage themselves, or clothes that change colour depending on lighting conditions.

Cephalopod skins have three layers. The top one consists of cells called chromatophores, which are sacs of coloured pigment, controlled by a ring of muscles. If the sac expands, it produces a pixel of colour; if it contracts, the pixel hides. These cells are responsible for hues like red, orange, yellow and black. The middle layer contains iridophores, cells that reflect the colours of the animal’s environment—they’re responsible for cooler colours like blues and greens. The bottom layer consists of leucophores, passive cells that diffuse white light in all directions, and act as a backdrop for the other colours.

The skin also contains light-sensitive molecules called opsins, much like those found in your retina. It’s still unclear what these do, but a reasonable guess is that they help cephalopods to “see” with their skin, and adapt their patterns very quickly without needing instructions from their brains.

The team drew inspiration from these skins when designing their own material. It consists of a 16 by 16 grid of squares, each of which consists of several layers.

  • The top one contains a heat-sensitive dye that reversibly changes colour from black at room temperature to colourless at 47 degrees Celsius, and back again. This is the equivalent of an octopus’s chromatophores.
  • The next layer is a thin piece of silver, which creates a bright white background, like the leucophores.
  • Below that, there’s a diode that heats the overlying dye and controls its colour. This is the equivalent of the muscles that control the chromatophores.
  • Finally, there’s a layer with a light-detector in one corner, a bit like a cephalopod’s skin opsins. All the top-most layers—the dye and the silver—have little notches missing from their corners so that the light-detector always gets a unimpeded view of its surroundings.
  • And the whole thing sits on a flexible base so it can bend and flex without breaking.

So, the light-detectors sense any incoming light, and tell the diodes in the illuminated panels to heat up. This turns the overlying dye from black to transparent. These pixels now reflects light from their silver layer, making them look white. You can see this happening in the videos below.  Here, different patches of light are shining onto the material from below, and it’s responding very quickly.

“There are analogies between layers of our system and those in the cephalopod skin, but all the actual function is achieved in radically different ways,” says Rogers. “The multi-layer architecture works really well, though. Evolution reached the same conclusion.”

“The most exciting thing about this is that it’s all automatic, without any external user input,” he adds.

There are obvious military applications for the device and the work was funded by the Office of Naval Research. But Rogers notes that the sheets are designed to sense and adapt—they don’t necessarily have to blend in. “There are a lot of applications in fashion and interior design,” he says. “You could apply these flexible sheets to any surface and create something that’s visually responsive to ambient lighting conditions. But our goal is not to make adaptable wallpaper; it’s on the fundamentals.”

Obviously, the material will have to be improved. Since it relies on heat to change colour, it’s relatively slow, consumes a lot of power, and only works in a narrow range of temperatures. But the team used a heat-sensitive dye because it was easy; it gave them time to focus on the rest of the system.

Now that this framework is in place, they think they could improve it very easily. Rather than heating diodes, they could use components that use changing electric fields. They could replace the dyes with other substances that offer a full range of colours, beyond just black and white. And they should be able to scale the sheet up easily—Rogers, after all, has a lot of experience in building flexible electronics using commonly used substances like silicon, rather than fancy (and expensive) new materials.

But he doubts he’ll ever make something that truly matches a cephalopod’s skin. “As an engineer looking at movies of squid, octopuses, and cuttlefish, you just realise that you’re not going to get close to that level of sophistication,” he says. “We tried to abstract the same principles and do the best we can with what we’ve got.”

Does their artificial skin have any advantages over what an octopus or squid can do?

“Well, it works on dry land!” says Rogers.

Reference: Yu, Li, Zhang, Huang, Malyrchuk, Wang, Shi, Gao, Su, Zhang, Xu, Hanlon, Huang & Rogers. 2014. Adaptive optoelectronic camouflage systems with designs inspired by cephalopod skins. PNAS http://dx.doi.org/10.1073/pnas.1410494111

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Octopus Cares For Her Eggs For 53 Months, Then Dies

In April of 2007, Bruce Robison sent a submersible into a huge underwater canyon in California’s Monterey Bay. At the canyon’s base, 1400 metres below the surface, he spotted a lone female octopus—Graneledone boreopacificacrawling towards a rocky slope.

The team sent the sub to the same site 38 days later and found the same female, easily recognisable through her distinctive scars. She had crawled up the slope itself and was guarding a group of 160 small, milky teardrops cemented to the rock. They were eggs.

For many a female octopus, laying eggs marks the beginning of the end. She needs to cover them and defend them against would-be predators. She needs to gently waft currents over them so they get a constant supply of fresh, oxygenated water. And she does this continuously, never leaving and never eating.

When the eggs hatch, she dies, starving and exhausted. As biologist Jim Cosgrove says, “No mother could give more”. You can watch a giant Pacific octopus going through this surprisingly moving sacrifice in the clip below from the BBC’s wonderful series Life.

Biologists rarely get a chance to measure how long these brooding periods last; at Monterey Bay, Robison’s team had a rare opportunity. For four and a half years, they returned to the same spot and found the same octopus, “clinging to the vertical rock face, arms curled, covering her eggs”.

She never left, and it’s possible that she didn’t eat for the whole time. Tasty crabs and shrimps crawled around her and she merely nudged them aside if they got too close. The team offered pieces of crab to her using a robot arm on their submersible; she turned them down. She may have occasionally grabbed nearby food or even eaten some of her own eggs, but the team found no evidence of this.

As the years went by, her condition deteriorated. When the team first saw her, her skin was textured and purple, but it soon turned pale, ghostly, and slack. Her eyes became cloudy. She shrank. And all the while, her eggs grew bigger, suggesting that they were indeed the same clutch.

The female octopus brooding her eggs in April 2007 (a), May 2007 (b), May 2009 (c), October 2009 (d), December 2010 (e) and September 2011 (f). The black circle and white arrows show distinctive scars on her arms. Image copyright Robison et al, 2014. MBARI. CC BY 3.0
The female octopus brooding her eggs in April 2007 (a), May 2007 (b), May 2009 (c), October 2009 (d), December 2010 (e) and September 2011 (f). The black circle and white arrows show distinctive scars on her arms. Image copyright Robison et al, 2014. MBARI. CC BY 3.0

The team last saw her in September 2011. When they returned in October, she was gone. Her eggs had hatched and the babies within had swum off to parts unknown, leaving nothing but tattered and empty capsules still attached to the rock. Her body was nowhere to be seen.

This epic brooding period—53 months in total—is the longest known for any animal. The famous emperor penguin—a model of parental sacrifice—incubates its egg for just 2 months. The record-holder among octopuses was a captive Bathypolypus arcticus who guarded her eggs for 14 months. Among animals that raise their young internally, elephants do so for 21 months, frilled sharks for 42, and alpine salamanders for 48. The female G.boreopacifica that Robison observed beat them all.

How did the octopus survive for so long? Her inactivity and the near-freezing water certainly helped. Sitting mostly still at just 3 degrees Celsius, her metabolism would have slowed to a crawl.

This marathon of maternal care makes sense for a deep-sea octopus. The longer she keeps it up, the bigger her young can grow and the greater their odds for survival when they hatch. And since she dies after brooding is over, she might as well keep at it for as long as possible.

Indeed, G.boreopacifica lays unusually large eggs that give rise to unusually large hatchlings. The clutches are also very small—for comparison, the giant Pacific octopus lays clutches of around 100,000). These are all signs of a reproductive strategy called K-selection, where mothers invest more effort into raising fewer offspring.

It’s clearly a successful strategy since G.boreopacifica is a very common species. Perhaps a 53-month brooding period is exceptional only because we have never had a chance to measure these periods before. As the team wrote, “These results only seem extraordinary when compared with well-studied shallow-water species; which indicates how little we really know about the deep sea.”

Reference: Robison, Seibel & Drazen. 2014. Deep-Sea Octopus (Graneledone boreopacifica) Conducts the Longest-Known Egg-Brooding Period of Any Animal. PLoS ONE 9(7): e103437. http://dx.doi.org/10.1371/journal.pone.0103437



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Why Octopus Arms Don’t Get Tangled

If you cut off an octopus’s arm, the severed limb will still move about for at least an hour. That’s because each arm has its own control system—a network of around 400,000 neurons that can guide its movements without any command from the creature’s brain.

The hundreds of suckers along each arm can also behave independently. If a sucker touches an object, it will change its shape to form a tight seal, and contract its muscles to create a powerful suction. It grabs and sucks, by reflex.

This setup allows the octopus to control its astonishing appendages without overly taxing its brain. Your arm has a small number of joints and can bend in a limited number of ways. But an octopus’s arm can create as many joints as it wants, in any direction, anywhere along its length. It can also extend, contract, and reshape itself. To control such infinitely flexible limbs, it needs to outsource control to the limbs themselves.

But what happens if one arm brushes past another? If the suckers grab objects on reflex, why aren’t octopuses constantly grabbing themselves by mistake?

To find out, octopus arm expert Benny Hochner teamed up with octopus sucker expert Frank Grasso.“Octopus suckers are undervalued in terms of their complexity,” says Grasso. “I’m one of their proponents. They’re really exquisite manipulation devices.”

Together with Nir Nesher and Guy Levy, the duo noticed that the suckers on a freshly amputated arm will never attach to another arm. Sure, they’ll grab skinned parts of an amputated arm or the bare flesh at the point of amputation, but not the arm itself. They’ll grab Petri dishes, but not those that are covered with octopus skin.

Common octopus. Credit: Pseudopanax.
Common octopus. Credit: Pseudopanax.

Octopuses clearly have some kind of sucker-proof coating on their own skin.  The team confirmed this idea by extracting chemicals from the skins of both fishes and octopuses, and applying these cocktails onto Petri dishes. They found that the octopus extract could block a sucker’s grabbing reflex but the fish extract could not.

“We all knew that octopuses are very dependent on chemical sensing but we haven’t done much research on this,” says Jennifer Mather from the University of Lethbridge, who studies octopus behaviour. “This paper will probably kick start it.”

Whatever the mystery chemical, it’s clear that octopuses can override its influence. The team showed that that living animals will occasionally grab amputated arms, even by the skin. Their brains can veto the reflexes of their suckers.

They can even tell if an amputated arm belonged to them or to another octopus. If they sensed another individual’s severed arm, they would often explore it, grab it, and hold it in their beaks in an unusual posture that the team called “spaghetti holding”. (Common octopuses will cannibalise their own kind, so a floating arm is fair game.) But when they sense their own severed limbs, they typically avoided it, and only rarely treated it like food.

“This gives us some idea of how octopuses might generate a sense of self—not by vision, which would be hopeless given their changeable appearance, but by chemical cues,” says Mather.

The octopus’s self-avoiding arms are a great example of embodied cognition—the idea that an animal’s body can influence its behaviour independently of its brain. As Andrew Wilson and Sabrina Golonka explain, “the brain is not the sole resource we have available to us to solve problems. Our bodies… do much of the work required to achieve our goals.”

The octopus… well… embodies this idea. Its brain governs many of its decisions and exerts control upon its arms, but the arms can do their own thing, including getting out of each others’ way. The animal doesn’t need to know the location of each of its arms to avoid embarrassing entanglements. It can let its arms do the work of evading each other.

This concept might be useful for designing robots. A typical robot, like Honda’s ASIMO, relies on top-down programs that control his every action. He can pull off pre-programmed feats like dancing or running, but he trips over even minor obstacles. He’s inflexible and inefficient. By contrast, Boston Dynamics’ Big Dog relies on embodied cognition. His springy legs are designed to react to rough terrain without needing new instructions from his central processor. (Thanks again to Wilson and Golonka for the examples.)

By studying the arms of octopuses, scientists may one day be able to design soft versions of Big Dog, pairing its flexible movements with an equally flexible chassis. Big Octopus, perhaps.

Reference: Nesher, Levy, Grasso & Hochner. 2014. Self-Recognition Mechanism between Skin and Suckers Prevents Octopus Arms from Interfering with Each Other. Current Biology. http://dx.doi.org/10.1016/j.cub.2014.04.024

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Cuttlefish Remember What, Where and When They Ate

You and I both have the ability to travel back in time… at least in our minds. For example, I can remember that last Monday, I was at my desk, writing a post about stomachless animals. You too have a seemingly endless catalogue of the whats, wheres and whens of your life.

This ability to remember the what, where and when of our past experiences is known as “episodic memory”. The term was first coined in the 1970s by Canadian psychologist Endel Tulving, who thought that such memories depended on language and were unique to humans.

He was wrong. In 1998, Nicky Clayton from the University of Cambridge published the first of many seminal experiments with western scrub-jays, showing that they can remember where they had stored food and which hoards were freshest. In other words, these bird brains also have episodic-like memories. We say “episodic-like” since we can’t really know if the animals store their what-where-when information into single coherent memories in the way that we do. Still, it’s clear that the components are there.

Since then, the episodic-like memory club has grown to include the great apes, rats, hummingbirds, and pigeons. But these are all mammals and birds. Christelle Jozet-Alves from Normandie University wanted to know if the same skills existed in animals that are very different to these usual suspects. She turned to the common cuttlefish (Sepia officinalis).

Like octopuses and squid, cuttlefish are cephalopods—a group of animals known for their amazing colour-changing skin and sophisticated intelligence. Cuttlefish are separated from birds and mammals by almost a billion years of evolution. But Jozet-Alves, together with Clayton and Marion Bertin, has shown that they too can “keep track of what they have eaten, and where and how long ago they ate”.

They are also soft-bodied and nutritious, which puts them on the menu of virtually every major group of ocean predator. Cuttlefish deal with these manifold threats through camouflage, defensive ink, and just plain-old hiding. They spend more than 95 percent of their time hiding in safe places. When they do venture out to search for food, it pays them to be quick about it. “Cuttlefish live fast and die young. They live less than two years, but their size drastically increases between hatching and old age,” says Jozet-Alves. “They definitely need to be very efficient when foraging if they want to grow as fast as possible.”

First, the team trained three cuttlefish to approach a black-and-white symbol to get a morsel of food—either crab, which they were fine with, or shrimp, which they vastly preferred. The cuttlefish also learned that the shrimp supply took a while to refill. If they approached the symbols within 3 hours of their last meal, they got nothing.

Next, Jozet-Alves presented them with two of the same symbols at different positions in their tank. The cuttlefish randomly approached one of the symbols, and Jozet-Alves dropped shrimp in front of one, and crab in front of the other.

She tested them an hour later. At this time, it would have been pointless to approach the shrimp symbol, since it wouldn’t have replenished. And the cuttlefish knew that—they almost always approached the crab symbol the second time around. But if Jozet-Alves tested them three hours later, they almost always approached the shrimp symbol instead. They knew that their favourite morsel would have replenished and that it was worth trying for it.

Schematic of cuttlefish experiment. Credit: Jozet-Alves et al, 2013. Current Biology.
Schematic of cuttlefish experiment. Credit: Jozet-Alves et al, 2013. Current Biology.

Their behaviour shows that they remember what (shrimp or crab), where (which symbol was associated with which food) and when (the time since they last ate). Admittedly, the team only tested three individuals but all of them behaved in the same consistent way. Like scrub-jays, chimps and hummingbirds, they have episodic-like memory.

But cuttlefish, being invertebrates, are very distantly related to these other members of the club. The only other invertebrates with a hint of the same abilities are honeybees, and they were only trained to go to the same place at the same time every day. That’s not quite the same as encoding information about specific events. Still, it’s clear that contrary to Tulving’s claims, the ability to encode what, where and when isn’t a uniquely human trait. It’s probably not even a uniquely vertebrate one.

Jennifer Mather from the University of Lethbridge, who studies cephalopod smarts, isn’t surprised. Years ago, she noticed that octopuses are “win-switch foragers”. That is, if they find food somewhere, they don’t visit it for a few days. “This paper isn’t the first behavioral evidence of episodic-like memory in an invertebrate, but it’s certainly the first experimental evidence of this capacity,” she says. “It underlines the tremendous flexibility and cognitive capacity of these very interesting animals.”

Jozet-Alves agrees. “Everyone who had the chance to work with cuttlefish have seen how amazing and fascinating they are,” she says. “At the same time, working with them is a real challenge to your patience. They are so shy that just making a cuttlefish eat in front of you can take sometimes days or even weeks. But once a cuttlefish gives you its trust, you just enjoy working with them and totally forget the hours waiting that they move out of their shelter!”

Reference: Jozet-Alves, Bertin & Clayton. 2013. Evidence of episodic-like memory in cuttlefish. Current Biology http://dx.doi.org/10.1016/j.cub.2013.10.021

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Squid With Feeble Tentacles Might Use Them As Fishing Lures

Most squid snatch their prey with a pair of extendable tentacles, which can shoot out at high speed. These muscular limbs are longer than the other eight arms, and end in a bulbous “club” that’s covered in suckers or hooks. Once they latch onto something, they rapidly contract and bring the prey in towards the squid’s sharp beak.

But one deep-sea squid—Grimalditeuthis bonplandi—is very different. Its tentacles are thin and fragile, and almost always break off when it’s captured. For ages, people thought it lacked tentacles altogether until a full specimen was found in the stomach of a fish. Weirder still, its clubs have neither suckers nor hooks. Instead, they are flanked by a pair of leaf-shaped membranes. Why?

Now, after observing a live individual off the coast of California, Hendrik-Jan Hoving from the Monterey Bay Aquarium Research Institute (MBARI) in California thinks he knows what how the squid uses its feeble tentacles. They’re not grasping limbs, but fishing lures. By waving the membranes, the squid uses its clubs to mimic the movements small animals and attract its prey.

For around 25 years, MBARI has been using remotely controlled subs to explore the waters around California’s Monterey Bay. Hoving frequently pilots these vehicles and he sees a lot of squid. But on 22 September 2005, he stumbled across his first specimen of Grimalditeuthis bonplandi. It was the first time that anyone had seen the creature alive in its natural environment.  

G.bonplandi lives all over the world, but this particular one was floating in a deep underwater canyon off the coast of California, 1000 metres or so below the surface. Its 14-centimetre body was largely transparent but flashed with neon pulses of red and violet. It hung there in the darkness at a slight tilt, beating its heart-shaped tail fins, arms splayed apart and tentacles outstretched.

“When we zoomed in for a close-up of the tentacle club, we saw it wiggling and undulating by flapping its membranes,” says Hoving. “We were really excited. It so strikingly resembled the movements of a small marine organism.”

G.bonplandi jetting away. It's arms are at the top-right and its mantle is point towards the bottom-left. Credit: MBARI
G.bonplandi jetting away. It’s arms are at the top-right and its mantle is point towards the bottom-left. Credit: MBARI

The team collected and dissected the Monterey specimen, and confirmed that its tentacle muscles were extremely thin and poorly developed compared to those of a related squid. There’s no way the animal could have used these limbs to handle prey. Indeed, when the squid wanted to bring its club towards its head, it seemed to swim towards the club rather than contracting the tentacle muscles.

Over the next five years, Hoving’s team observed six more of these squid in the Gulf of Mexico, and all of them behaved in the same way. Their clubs tips all gently undulated like some small swimming animal.

Judging by their stomach contents, we know that G.bonplandi eats shrimp, other small crustaceans, and even other small squid. Hoving thinks that the squid could use its undulating clubs to lure in these victims in three possible ways: by disturbing glowing creatures in the water and creating temporary flashes; by creating attractive low-frequency vibrations; or by creating waves of moving water that mimic small swimming animals. Of course, how the squid then grabs any incoming prey is an open question.

Many predators use lures to attract their victims. Anglerfish, viperfish and dragonfish have lures projecting from their heads. Alligator snapping turtles wriggle their pink tongues like wriggling worms. Many vipers do the same with their tails, and one even has a tail that looks like a spider. The assassin bug (Stenolemus bituberus) kills spiders by strumming their webs in the style of a trapped and struggling insect. In a fit of perverse irony, the cookie-cutter shark uses a glowing collar to lure in larger predators, which it then eats.

It’s entirely plausible that some squids use similar tactics. The stubby squid buried itself in sand but wiggles one outstretched arm. The deep-sea squid Chiroteuthis calyx has glowing organs on its tentacles, which might help to attract fish. Another squid, Octopoteuthis deletron might use the glowing tips of its (freakishly detachable) arms in a similar way. None of these possible examples of luring have been proved, and the same goes for G.bonplandi.

Edith Widder, a marine biologist and deep-sea explorer, says the idea is plausible. “I wish they had had some way to check for the amount of bioluminescence in the water column where they observed the squid,” she says. “I also think the idea that it could produce a hydrodynamic signal has merit.  If you think about the enormous challenge these animals face, locating food and mates in such vast volumes of darkness you have to believe they must have come up with some pretty clever solutions.”

“We are very far from doing experimental work on these animals as we encounter them so rarely,” admits Hoving. “We had moments of good fortune which allowed a peek into the lives and behaviour of this poorly known species. Hopefully, with increasing application of underwater technology and exploration of the water column, we will be able to learn more about Grimalditeuthis and other inhabitants of the world’s largest ecosystem.”

Reference: Hoving, Zeidberg, Benfield, Bush, Robison & Vecchione. 2013. First in situ observations of the deep-sea squid Grimalditeuthis bonplandi reveal unique use of tentacles. Proc Roy Soc B http://dx.doi.org/10.1098/rspb.2013.1463

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How To Terraform A Squid

Terraforming—the act of transforming an inhospitable world into one that we can live on—has been a staple of science-fiction for decades. But some living things have been carrying out their own version of the practice for far longer.

The bacterium Vibrio fischeri is a squid terraformer. Although it can live independently in seawater, it also colonises the body of the adorable Hawaiian bobtail squid. The squid nourishes the bacteria with nutrients and the bacteria, in turn, act as an invisibility cloak. They produce a dim light that matches the moonlight shining down from above, masking the squid’s silhouette from predators watching from below. With its light-emitting microbes, the squid becomes less visible.

Margaret McFall-Ngai from the University of Wisconsin has been studying this partnership for almost 25 years and her team, led by postdoc Natacha Kremer, have now uncovered its very first moments. They’ve shown how the incoming bacteria activate the squid’s genes to create a world that’s more suitable for their kind. And remarkably, it takes just five of these microbial pioneers to start the terraforming (teuthoforming?) process.

Inside its egg, an embryonic squid is sheltered in a sterile bubble. When it hatches, it starts pumping seawater into its body, bringing a flood of bacteria into contact with a special light organ. Among these teeming hordes is V.fischeri. It gathers in the layer of mucus on the light organ’s surface, squeezes through six tiny pores, and multiplies to fill the various nooks and crannies within.

To understand the first moments of this partnership, Kremer raised baby squid in either normal Hawaiian seawater, or water that contained all the usual bacteria except for V.fischeri. By comparing the two groups, she could “eavesdrop into the very first conversations of an animal host with its coevolved partner”.

She found that the light organs can sense the presence of just five V.fischeri cells among millions of other bacteria. These microbes touch just two or three of the squid’s own cells at most, but that’s enough to change the activity of 84 genes across the whole light organ.

Several of these genes are involved in the squid’s immune system. The team suspects that they may activate antimicrobial chemicals in the mucus, to create an environment that’s inhospitable for other bacteria besides V.fischeri. This might explain why the light organ is exposed to hundreds of bacterial species, but only V.fischeri can colonise it.

Kremer also showed that V.fischeri switches on a squid gene that breaks down chitin, a large molecule found in the mucus around the light organ. The chitin is converted into a smaller molecule called chitobiose, which the bacteria can sense. And once they detect chitobiose, they become attracted to it.

So, when V.fischeri reaches the light organ, it starts destroying chitin and making chitobiose. Chitin is especially abundant near the pores and internal ducts, so these areas eventually teem with chitobiose. And that produces an alluring signal that draws other V.fischeri towards the pores and into the light organ itself. The first few bacteria that go down this route lay down a chemical trail that many more follow.

All of this happens in the hours after hatching. By tweaking the genome of their hosts, a few bacteria can make the squid more attractive to their peers and less conducive to their competitors.

Studies like this aren’t just relevant to squid. We are also colonised by trillions of bacteria in our first moments of life. The squid gets its bacteria from the surrounding water, and we get ours from our mothers—from her vagina if we’re born naturally, or from her skin if we’re born through C-section. Our microbes might not glow or hide us like the squid’s partners, but they do change the properties of our guts, help to control our immune system, and might even shape our behaviour as we grow up. Perhaps by studying the squid, we’ll learn more about how our own terraformers shape our bodies to their needs.

Reference: Kremer, Philipp, Carpentier, Brennan, Kraemer, Altura, Augustin, Hasler, Heath-Heckman, Peyer, Schwartzman, Rader, Ruby, Rosenstiel & McFall-Ngai. 2013. Initial Symbiont Contact Orchestrates Host-Organ-wide Transcriptional Changes that Prime Tissue Colonization. Cell Host and Microbe http://dx.doi.org/10.1016/j.chom.2013.07.006

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The Global Kraken

Earlier this year, the Discovery Channel released the first ever footage of the legendary giant squid in its natural environment. But did the crew manage to film the giant squid, or one of the giant squids?

The giant was first described by the Danish naturalist Japetus Steenstrup in 1857, who named it Architeuthis dux. As Craig McClain writes, the name “translates to ‘most important squid leader’.  That is scientifically an awesome name.” Since then, biologists have slapped the Architeuthis brand on no fewer than 21 potential species. Some of these over-eager taxonomists were just going on fragments of flesh, like beaks or arms that sperm whales had coughed up. Others reasoned that squid remains in far-off corners of the world must belong to different species. After all, giant squids are everywhere—they’ve turned up in all oceans except the waters around Antarctica.

How many of these species are valid? “All of them” seems unlikely as an answer. Some people think that there are just three, which live in the North Atlantic, North Pacific, and Southern Ocean respectively. Others insist that there’s just the single globe-spanning species, caressing the world in its tentacles.

The distribution of giant squid around the world. Image created by NASA, from Wikipedia.
The distribution of giant squid around the world. Image created by NASA, from Wikipedia.

Now, a team of scientists from eight countries, led by Inger Winkelmann from the University of Copenhagen, has tried to settle the debate by looking at the kraken’s genes. Together, they amassed tissue samples from 43 giant squids caught all over the animal’s range, from Florida to South Africa to New Zealand. They sequenced each sample to piece together its mitochondrial genome—a small secondary set of DNA, which sits outside the main genome in tiny bean-shaped batteries.

The team found that the giant squid’s genetic diversity is incredibly low. Even though the individuals hailed from opposite corners of the world, they differed at less than 1 in every 100 DNA letters. For comparison, that’s 44 times less diverse than the Humboldt squid, which only lives in the eastern Pacific. In fact, the giant squid seems to be genetically narrower than any other sea-going species that scientists have tested, with the sole exception of the basking shark.

This strongly suggests that the 21 proposed species of giant squid can indeed be collapsed into one. There’s just the one global kraken—Architeuthis dux, the one-and-only original. What’s more, the population seems to have very little structure—in other words, squids that hail from nearby waters aren’t going to be genetically closer than distant individuals. The mitochondrial DNA of a Japanese squid is basically the same as that of a Floridian squid.

Why? It’s possible that the adults are wandering nomads that swim over large areas, but that seems unlikely. Chemical analyses of their beaks suggest that they stick within a relatively contained patch of ocean.  The alternative is that they go a-wanderin’ as larvae and youngsters. Young marine animals are certainly capable of passively drifting over tens of thousands of kilometres on ocean currents, so it’s entirely possible that the squids do the same. These young nomads would feed on plankton and other small creatures until they became big, whereupon they’d settle down and sink to the nutrient-rich waters of the deep ocean.

“I am not in the least surprised by their findings,” says giant squid expert Steve O’Shea. “They support what has been said many times earlier by some, contradicted by others and debated by a few, to what end I will never know.” O’Shea himself has suggested that larval giants drift over considerable distances and, on another Discovery Channel-sponsored research trip, he has captured 17 of these larvae at the surface of the ocean.

Craig McClain from the National Evolutionary Synthesis Center is more enthusiastic. “This is the research project I dreamed of conducting, and the results are even more interesting than I would have imagined,” he says. “The finding of just one species is not unexpected, but the study finally provides the molecular evidence that was so sorely missing.  What is amazing is the total lack of genetic structure among ocean basins. I know of few animals that have the long range dispersal ability or behavior to ensure genetic exchange over such great distances.”

But why does the squid have such low genetic diversity? Winkelmann couldn’t find any signs that its mitochondrial DNA evolves at a slower pace than that of other animals. Instead, it’s possible that the giant squid—like the basking shark—went through a population bottleneck at some time in its past, and today’s individuals descended from that narrow stock of ancestors. Maybe they used to be restricted to a specific part of the world but were released by some ancient event, like a change in climate, or the death of a competitor.

This is all just guesswork. As Winkelmann writes, “We cannot offer a satisfactory explanation for the low diversity.”

And there’s one last, important caveat—the team’s conclusions are based on the mitochondrial genome alone. That’s useful for looking at things like diversity and ancestry, but the team still need to analyse the giant squid’s nuclear genome, which contains the vast majority of its DNA. Nuclear genomes have a habit of complicating the stories told by mitochondrial ones. Who knows what they will do for the giant squid?

“It is clear that there is much that remains an enigma about these ocean giants,” says McClain.

Reference: Winkelmann, Campos, Strugnell, Cherel, Smith, Kubodera, Allcock, Kampmann, Schroeder, Guerra, Norman, Finn, Ingrao, Clarke & Gilbert. 2013. Mitochondrial genome diversity and population structure of the giant squid Architeuthis: genetics sheds new light on one of the most enigmatic marine species. Proc Roy Soc B http://dx.doi.org/10.1098/rspb.2013.0273

Flight of the Squid

This morning, I received a strange letter. The envelope carried the subtle scent of the sea, and the immaculate lettering on the front was clearly and carefully written in actual ink. The note inside read:

Dear Brian,

I am but a lowly squid, dashing through the water, and nomming what I can, even my own kind. While I have the freedom of the water, I have always wanted to fly! I see the flying fish and I get so jealous! Can you help?

In hope,

Sad Sea Squid

PS: Do you think the girls would think it was cool if I flew?

I hadn’t expected to start fielding pleas for advice from disconcerted marine life. But who am I to refuse a cephalopod’s aeronautic dream? Since the letter contained no return address – and my efforts to get the post office to send a letter to the middle of the Pacific proved fruitless – I can only hope that the somber squid is able to read my response here.


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Giant Squids Have Huge Eyes to See Shiny Charging Whales

Discovery Channel viewers have been able to look into the eye of the giant squid, in the first ever footage of this elusive predator in its natural environment. In honour of this achievement, I’m republishing this story from last year, about why the squid’s eyes are so ridiculously big, even for its already huge body.


The giant squid sees the world with eyes the size of soccer balls. They’re at least 25 centimetres (10 inches) across, making them the largest eyes on the planet.

For comparison, the largest fish eye is the 9-centimetre orb of the swordfish. It would fit inside the giant squid’s pupil! Even the blue whale – the largest animal that has ever existed – has measly 11-centimetre-wide eyes.

So why the huge leap in size? Why does the giant squid have a champion eye that’s at least twice the size of the runner-up?

Dan-Eric Nilsson and Eric Warrant from Lund University, Sweden, think that the squid must have evolved its eye to cope with some unique challenge that other animals don’t face – to spot one of the world’s biggest predators, the sperm whale.

It’s generally true that bigger eyes can see more light. You’d expect that a big-eyed squid should be able to see further than a small-eyed one, which would be useful for finding mates or prey. But Nilsson and Warrant showed that this intuitive explanation can’t account for the squid’s extreme eye.

Using a mathematical model, they found that in the deep ocean, eyes suffer from a law of diminishing returns. Small eyes can see dramatically further if they grow a bit bigger. But once the pupil passes 2.5 centimetres, these improvements become tinier and tinier. Once the pupil reaches 3.5 centimetres, and the eye itself reaches 9 centimetres, there’s very little point in making it any bigger. And that’s exactly where fish have stopped. Even though the swordfish’s head is capable of holding a much larger eye, it doesn’t.

The giant squid weighs about the same as a swordfish, but its eye is around three times bigger. Why? Using their model, Nilsson and Warrant found that enormous eyes have advantages over eyes that are merely large. Specifically, they’re much better at spotting other large objects that give off their own light, in water deeper than 500 metres. There’s one animal that fits those criteria, and it’s one that giant squids really need to see: the sperm whale.

We know that sperm whales eat the giant squid and its even larger cousin, the colossal squid. The sharp beaks of both species have been found in sperm whale stomachs, and the whales often bear the marks of their battles in their skin – ring-shaped scars caused by the serrated ‘teeth’ on the squids’ suckers.

Hold on – whales don’t glow. In the dark oceans, how could the squids see them? Nilsson and Warrant note that while sperm whales don’t produce their own light, they frequently disturb animals that do. When they dive, they knock tiny animals like jellyfish and crustaceans that flash in response.

These shimmering outlines would be too faint for most animals to see, but not the giant squid. Nilsson and Warrant showed that its huge eyes could pick up this light from 120 metres away, and they can scan a huge sphere of water for those tell-tale flashes.

Sperm whales have a long-range detector too – sonar. They produce extremely loud clicks, and time the rebounding echoes to map the water around them. Their sonar has a range of a few hundred metres, so it should always spot a giant squid before the squid sees it coming.

Still, the squid’s eye would give it enough warning to allow it to flee. Nilsson says, “Squid are generally good at fast bursts, and the few observations that have been done on live giant squid show that they are powerful animals.“ They also have large bodies, which could help them to escape at speed. Perhaps the threat of sperm whales pushed the evolution of both the giant squid’s eyes and its body.

This arms race between giant predators and giant-eyed prey may have played out once before. During the reign of the dinosaurs, reptiles called ichthyosaurs swam in the seas. They looked a bit like dolphins, but they also had massive eyes – similar in size to those of the giant squid. There were no sperm whales around in those days, but there were other massive predators like Kronosaurus and Rhomaleosaurus. Maybe the ichthyosaurs used their large eyes to avoid these giant hunters, just as giant squids use theirs to avoid sperm whales.

For now, Nilsson and Warrant bill their idea as a hypothesis, albeit one with a solid foundation. “To confirm or disprove our theory it would be necessary to make direct observations on how giant and colossal squid evade hunting sperm whales,” says Nilsson. “But because this takes place in the darkness at depths of 600-1000 metres in the sea, such observations are extremely difficult.”

A note on sizes: Very few people have successfully measured the eye of a giant squid. In the few successful attempts, the eyes belonged to dead animals and were distorted. Thankfully, Nilsson and Warrant managed to get a photo of a freshly caught giant squid, captured by a Hawaiian fisherman in 1981. There’s a standard fuel hose running over the eye, and the duo used this to gauge its size – it was at least 27 centimetres wide. They also got access to a colossal squid – the largest one ever caught – which had been frozen in New Zealand’s Te Papa Museum. Its eye was the same size – 27 to 28 centimetres. There are some larger estimates of 40 centimetres or so, but the duo think that these are overblown.

Reference: Nilsson, Warrant, Johnsen, Hanlon & Shashar. 2012. A Unique Advantage for Giant Eyes in Giant Squid. Current Biology http://dx.doi.org/10.1016/j.cub.2012.02.031

Photo: squid by National Geographic, eye by Ernie Choy

Giant Squid – From Sea Monster to Conservation Icon

When I was five years old, shortly after my dinomania hit a fever pitch, my parents took me to New York City’s grand American Museum of Natural History. The towering, tail-dragging Tyrannosaurus and low-slung, wrong-headed “Brontosaurus” were the species I most wanted to see on my fossil safari, but I didn’t only have eyes for the Mesozoic. Anything suitably large and monstrous shocked my imagination, including the dim diorama of a sperm whale tussling with a giant squid.

The life-scale model was artificial – I can’t even imagine how anyone would go about mounting an authentic giant squid – but the fantastic scene drew me in because there was the distinct possibility that such an epic battle was actually taking place at that very moment. The dinosaurs in the upper halls were all gone. They only lived where speculation and science melded together. But the giant squid and sperm whale didn’t need me to try to revive them. That dark, static vision was a three-dimensional snapshot of a living truth.

As a child, I was convinced that the squid had as much a chance of winning the battle as the whale. The toothed cetacean had brute strength, certainly, but I believed that the slippery squid was crafty enough to ensnare and drown its attacker. The giant squid was a real sea monster, after all, and only a foolish predator would trifle with a 50 foot cephalopod. Only later did I face the ugly fact that the squid was not an equal in combat, but prey. Sperm whale stomach contents leave no doubt that giant squid are little more than tasty morsels for the marine mammals. All that’s usually left of the titanic cephalopods are their tough, keratinized beaks.

So if giant squid don’t actually hunt sperm whales, sink ships, or devour rum-soaked pirates, what do they eat? And how do they catch their food? Discovery’s Monster Squid: The Giant Is Real, due to air this Sunday, might offer a few clues through the first video footage of Architeuthis dux in its deep sea haunts, but marine biologists actually know quite a bit about the feeding habits of this elusive cephalopod thanks to stranded specimens and beaks.


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Master of masters of camouflage

Few animals are better at blending into their backgrounds than the cephalopods—the class of marine camouflage experts that includes octopuses, squid and cuttlefish. And few people know more about their tricks than Roger Hanlon.

Ever since the age of 21, when an octopus took him by surprise on a snorkelling trip, Hanlon has been enchanted by their disappearing acts. Within fractions of a second, they can change the colour, texture and shape of their bodies to perfectly match those of their environment. Just look at this incredible octopus video that Hanlon took:

I’ve written about Hanlon’s work, and about the secrets of cephalopod camouflage, for Mental Floss. Head over there to read more about why cephalopods evolved such incredible abilities, how their infinitely varying patterns are actually more constrained that they seem, and how Hanlon is now trying to duplicate squid skin with synthetic materials.