Out of Office

Hi friends,

I'm very excited to share with you that Inkfish has moved to a new ocean-floor crevice. You can now find me at blogs.discovermagazine.com/inkfish. It's all the same inky goodness, now hosted by Discover.

Since you've been kind enough to read my stories, speculations, and sometime absurdities over here, I hope you'll update your RSS feeds to http://feeds.feedburner.com/ink-fish or use whatever other technological tricks will take you with me to the new site. I'm deeply grateful to everyone who reads and shares these posts. Without you I would just be talking to myself about fake squid testes, and that would be weird.

Thanks also to Field of Science for plucking me from the blogspot muck and giving me a friendly home since 2011. Anchors aweigh!

—Elizabeth

For Diguise, Female Squid Turn On Fake Testes

The best way to stay out of trouble, if you're a shimmery, color-changing little squid, might be to paint on some pretend testes. Scientists have found that certain female squid can switch on and off a body pattern that makes them look male. They use a never-before-seen cell type to do it, and it may be all for the sake of keeping the actual testes owners far away.

The opalescent inshore squid, Doryteuthis opalescens, lives in the Eastern Pacific and is one of the main species caught for food in the United States. So you'd think someone would have noticed its trick before. But the animals shift their colors all the time, and no one seems to have paid much attention to a certain bright stripe particular to females.

Daniel DeMartini, a graduate student at the University of California, Santa Barbara, "observed the female squid rapidly switching the stripe on and off," says his advisor, Daniel Morse. He decided to gather a few hundred D. opalescens squid in laboratory tanks and watch them work.

DeMartini found that females can opt to turn on a bright white stripe on their mantles, highlighted by a line of iridescence on both sides. This happens to look pretty similar to a male squid's testis, which—in his less colorful moments—is visible as a long white shape inside his transparent body.

The authors speculate that female squid might use this stripe as a disguise when they want to avoid harassment by males. "In this species of squid, mating occurs in dense assemblages of animals, with the females subject to repeated bouts of mating by multiple males," Morse says. By switching on her white stripe and mimicking a male, a lady squid might be able to fend off some of these mating attempts, protecting both herself and any fertilized eggs she's carrying.

Morse is less excited about this act of deception, though, than he is about the cells that squid use to pull it off. Within the white stripe region, specialized cells hold proteins called reflectins inside many spherical packages. These proteins start out colorless. Upon receiving a signal from the brain, the packages shrink into dense blobs. The varying sizes of the blobs make them reflect all different wavelengths of light, so that the cells as a whole appear bright white. It's the same way we humans make white paint, Morse says: small, dense particles of titanium dioxide are suspended in the liquid, and the combination of different-sized particles ensures all light waves are reflected at once.

Earlier, the authors found reflectins in the same squid's color-changing cells. Instead of turning from transparent to white, these cells can move between many different colors. In this case, "the reflectins are packed in accordion-like folds or pleats in the cell membrane," Morse says. When the brain tells the proteins to clump together, the accordion folds close up—and depending how far they close, the cells will reflect different wavelengths of light, from red all the way to blue.

It's fitting that squid have ten arms, because this one seems to have a surprise up every sleeve. As to whether it's still hiding anything more surprising than fake testes, we'll have to wait and see.


Daniel G. DeMartini, Amitabh Ghoshal, Erica Pandolfi, Aaron T. Weaver, Mary Baum, & Daniel E. Morse (2013). Dynamic biophotonics: female squid exhibit sexually dimorphic tunable leucophores and iridocytes. Journal of Experimental Biology : 10.1242/​jeb.090415

Images: DeMartini et al. (Top: a close-up view of an iridescent stripe in a female.)

On the Road with Crabs

I'm still on the road, so there won't be any new posts until next week. (One highlight from the trip so far has been a pair of signs we passed in Western New York late at night. The top sign read "CORRECTIONAL FACILITY AREA." Underneath: "DO NOT PICK UP HITCHHIKERS.")

In the meantime, here are a couple favorite travel-related stories from the past.

This Penguin: An Unexpected Journey (January 2013)
Lost baby penguins wearing earmuffs.


Monitoring from Space Shows Even This Giant Crab Can Navigate Better than You (November 2012)
Who doesn't love land crabs?

Another highlight was a radio station we picked up somewhere in Indiana with the tagline, "It's not just a bunch of random songs. It's a bunch of random songs you really like!" See you later this week, by which time I may have adapted that into a new blog descriptor.

Happy Blogday! Help Me Rename This Site

Inkfish is three years old today!

One great thing about blogs that doesn't apply to real three-year-olds is that you can change their name and appearance at will. I'm getting tired of "Inkfish"—too mysterious, too many creepy arms. Too much guilt about mistakenly calling octopus arms "tentacles" on occasion.

So I'd like to give the blog a new name and a new look. Below are several directions I'm considering. I hope that you, readers, will weigh in.

**********

Welcome! You Probably Got Here by Googling Your Juice Cleanse Symptoms
Tagline: Or Searching for Ionic Foot Detox Reviews
Alternate tagline: I Write About Other Stuff Too. Check It Out When You're Less Hazy
Banner art: a weeping woman with her feet in a small tub of brown water. Foregrounded, a glass of kale juice with a party umbrella.
Inspiration: juice cleanses, foot detox, everything else.

Why I Couldn't Hang Out Last Night
Banner art: a blogger on a couch in a dark room, gently lit by the glow of the laptop screen.
Inspiration: purely fictional.

Every Study About Penguins
Banner art: penguins.
Alternate art: not penguins. Irony could increase my readership among hipsters.
Inspiration: penguins, penguins, penguins, penguins, penguins.

The Loom
Banner art: portrait of Carl Zimmer.
Inspiration: trying to lure Bing users who are searching for Carl Zimmer's blog, The Loom.
Potential complication: lawsuit.

Animals with Things on Their Heads
Banner art would be a rotating selection of photos: crabs wearing GPS devices, pigeons carrying cameras, penguins with earmuffs, and this seal.

Inspiration: animal stalking, pigeons.

Girl That Poops Flowers
Alternate title: Most Inconvenient Moments to Have Narcolepsy
Banner art: a mouse that's quiet—too quiet.
Inspiration: unusual internet searches addressed at the help desk.

Adventures in Bodily Fluids: An Ongoing Quest to Make My Grandmother Admit She Doesn't Love Everything I Write
Banner art: the empty vanilla ice cream bowl I considered using to illustrate a story about sperm-eating flies.
Inspiration: see above.

**********

Please leave your votes in the comments (or just say hello). Thanks for your help, and thanks as always for reading!

Squid's Daily Rhythms Are Controlled by Glowing Symbiotic Bacteria

At nightfall, the Hawaiian bobtail squid digs itself out of the sand and rises into the ocean water like a spaceship taking off. It switches on its cloaking device: glowing bacteria inside its body light up, disguising the squid's silhouette against the moonlight for any predators swimming below. As sleek a vehicle as it appears, though, the bobtail may not totally outrank its microscopic crewmembers. The bacteria seem to power a clock inside the squid's body that can't function without them.

Hiding during the day and hunting at night in shallow Pacific waters, Euprymna scolopes clearly has a working circadian clock. Researchers had noticed, though, that the squid's light organ—the specialized pocket inside its body that houses its bacterial helpers—seemed to have a rhythm of its own. The Vibrio fischeri bacteria give off fluctuating amounts of light throughout the day, for one thing. And the bacteria have their own daily rhythm of gene expression (when various genes are turned on or off), explains Margaret McFall-Ngai, a microbiologist at the University of Wisconsin, Madison.

McFall-Ngai and her coauthors looked for genes linked to circadian rhythms within the squid. They found two types of "cry" genes, which are known to control internal clocks throughout the animal and plant kingdoms. One gene had a daily cycle of activity in the squid's head—which is what you'd expect, since animals' main circadian clocks are in our brains. Other clocks can be elsewhere in the body, though, and this is what researchers found with the second cry gene. It was cycling only within the light organ.

Baby squid, which hadn't yet collected bacterial friends in their light organs, didn't show the same cycling. So it seemed that the bacteria themselves were driving the daily rhythms in the light organ. When the researchers let squid fill their light organs with defective, non-glowing bacteria, the cry gene still didn't cycle properly. This suggested that the glow of the bacteria was the crucial ingredient.

To test this idea, the scientists shone a blue light on the squid holding defective bacteria. Now they expressed just as much cry as the original squid.

McFall-Ngai explains that cryptochromes, the proteins made by cry genes, respond to blue light. Based on the light signals the cryptochromes receive, they turn other genes on or off. Cryptochromes in the squid's head respond to light from the sun to drive its daily rhythms, as in other animals and plants. Those in its light organ, though, respond to the light of its glowing bacterial companions.

The role of the bacterial clock isn't clear yet. "We don't know if the light organ rhythms control any other rhythms in the body," says McFall-Ngai. "But they certainly seem to be involved in controlling the rhythms of the organ itself." The squid controls the daily schedule of the bacteria, too: it jettisons most of its bacteria in the morning, and seems to keep them dimmed during the day by restricting their oxygen supply. At night, it gives the bacteria enough resources to glow at full strength—and that glow drives the clock within the light organ. "There seems to be a tit for tat," McFall-Ngai says. "The host and symbiont 'talk' to one another, controlling one another's biology."

The idea that bacteria can drive circadian rhythms inside their hosts is exciting to humans because we, too, are animals packed full of bacteria. Ours don't glow, but they do line our guts and participate in digesting our food. McFall-Ngai points out that scientists have found "profound circadian rhythms" within our gut tissues, both in their activity and in what genes they express.

Even though we're land-bound, non-glowing vertebrates, our bacteria could be powering circadian rhythms within our bodies just like the squid's. "We think it might be a very general phenomenon," McFall-Ngai says. Our microscopic passengers, that is, might be helping to steer the spaceship.


Heath-Heckman, E., Peyer, S., Whistler, C., Apicella, M., Goldman, W., & McFall-Ngai, M. (2013). Bacterial Bioluminescence Regulates Expression of a Host Cryptochrome Gene in the Squid-Vibrio Symbiosis mBio, 4 (2) DOI: 10.1128/mBio.00167-13

Image: Margaret McFall-Ngai

Play Along as Sub Discovers Sunken Whale Bones Crawling with New Life Forms

Forget a needle in a haystack. For that search you'd be allowed light and air—and when you held the needle in your hand at last, it wouldn't be unrecognizably coated in bone-eating worms. Looking for whale skeletons on the ocean floor is such an impossible task that no one sets out to do it on purpose. The most recent find, lying near Antarctica and crawling with previously unseen species, was a very happy accident.

A dead whale that sinks all the way to the ocean floor is called a "whale fall," kind of like "windfall," which it is. The corpse is a massive sack of food dropped from above into a barren landscape. It feeds generation upon generation of life: first the scavengers that pick it clean, then other creatures that chew the bones into scaffolding and bacteria that churn out sulfides, and then a host of animals that feed on these chemicals directly or indirectly.

The same types of animals live at hydrothermal vents and cold seeps, where they consume sulfides and other chemicals seeping out of the earth. Whale falls may act as stepping stones for these species to migrate from one undersea chimney to the next. Even though they haven't seen many sunken skeletons up close, scientists have deduced this with the help of experiments such as dropping wood piles into the ocean and leaving them there.

When the members of a UK-funded research expedition came across the latest whale fall, they were piloting a remotely operated vehicle (ROV) more than 1,440 meters under the sea. "We were at the end of a very long ROV survey," says graduate student Diva Amon, "and had already gone an hour over our allocated time on the seafloor." Then, she says, "we spotted a row of curious white blocks in the distance."

Investigating more closely, the team realized that the blocks were spine bones. They were looking at a whale skeleton covered in deep-sea animals. "We all realized that this was only the sixth natural whale fall to be seen, and the first in the Antarctic," Amon says. "Everyone was thrilled."

In this video, you can watch from the eyes of the ROV as it pans across the find. The camera moves from the whale's skull to its vertebrae, which are lined up like a string of enormous marshmallows. Then it zooms in to see the lush jungle of life sprouting from each bone. Around 50 seconds in, you'll get a cephalopod surprise (is there a better kind?).

The fronds you see waving from the vertebrae are the tail ends of bone-eating worms called Osedax, which Amon calls "remarkable." Tucked in between them are the shells of limpets. When the camera pans down to a fellow who looks like a rubbery sock (a sipunculan worm), you might spot tiny crustaceans scurrying across the bone in the background. Did you see the worm whisk itself into hiding when the squid jetted by? You should probably watch again to be sure.

If the pale denizens of this skeleton look weird to you, they were weird to the scientists back at sea level too. The creatures at the whale fall included nine species that had never been seen before. "Every time one explores the deep sea, there is a very large chance of finding a new species," Amon says.

DNA analysis showed that the skeleton, nearly 11 meters long, once belonged to a minke whale. The types of creatures now living on it were similar to those at other whale falls. Based on these life forms and the state of the bones, scientists could tell that the whale fall has become a sulfur-rich environment. It houses the same animals that inhabit deep-sea vents and cold seeps, and it may be helping those creatures migrate across the ocean floor. "One species of limpet that was found on the whale bones was also found on nearby hydrothermal vents," Amon says.

The researchers couldn't tell whether the skeleton had been in its resting place for a few years or for several decades. Either way, they left this rare needle right where they found it.


Amon, D., Glover, A., Wiklund, H., Marsh, L., Linse, K., Rogers, A., & Copley, J. (2013). The discovery of a natural whale fall in the Antarctic deep sea Deep Sea Research Part II: Topical Studies in Oceanography DOI: 10.1016/j.dsr2.2013.01.028

Images: Whale vertebrae photo and video (c) UK Natural Environment Research Council ChEsSo Consortium; deep-sea creatures (c) Natural History Museum.

Baby Cuttlefish Are Cute, Colorblind Killers

The business end of a cuttlefish is no place a small crustacean wants to be. Cuttlefish are hunters who creep around in camouflage—virtually indistinguishable from a gray patch of gravel or a branching green seaweed—then lash out with their tentacles, turning a passing shrimp into shrimp toast. Oh, and they're colorblind. Despite this apparent handicap, though, learning to hunt doesn't take a lifetime. Baby cuttlefish figure it out almost as soon as they hatch.

"Newly hatched cuttlefish are mini adults," says Anne-Sophie Darmaillacq of the Université de Caen Basse-Normandie in France. They behave similarly to full-grown cuttlefish, that is, and look like toy versions of their parents. Yet those grownups are long gone. "Parents die after the spawning season," Darmaillacq says. Since cuttlefish are born as orphans, they have to be able to look after themselves right away.

For this reason, Darmaillacq and her coauthors wondered how the eyesight of junior cephalopods compares to that of their adult relatives. To find out how quickly a just-hatched cuttlefish's eyes get up to speed, they collected eggs of the cuttlefish Sepia officinalis off the coast of France. (The genus name describes a cuttlefish's brown ink, not its many-colored body.)

 Zero to 30 days after hatching in the lab, the tots were tested in a carousel-like device. While a cuttlefish sat stationary at the center, a cylindrical screen with vertical stripes rotated around it at various speeds. Animals that were able to distinguish the stripes spinning by would follow them with their eyes, or by rotating their whole bodies. One set of test screens had black, white and gray stripes. Another had stripes that produced different polarizations of light.

Human eyeballs don't distinguish light polarization, which is when light waves all wiggle in the same orientation as they travel, as after passing through a filter. Bees and some other animals can see this polarization and use it to navigate. Cuttlefish, too, can see light polarization, and scientists are familiar with the architecture in a cuttlefish's retina that allows this. But Darmaillacq says the ability hadn't been studied as much in young cuttlefish.

The tests in the striped carousel showed that cuttlefish who had just hatched were already great at tracking black, white and gray stripes, and got even better over their first 30 days of life. They also started life with some skill at seeing stripes of light polarization, and improved as they aged.

Watching stripes spin is less important than knowing when to pounce on a passing meal, though. In a second set of experiments, the researchers showed young cuttlefish two types of prey trapped inside glass tubes and waited to see which the cuttlefish would attack. One prey was mysid shrimp, which hide by being transparent—but they're much easier to spot if you can see light polarization. The other prey was crabs, which both cuttlefish and humans can see without the help of polarized light.

In a regular glass tube, cuttlefish eagerly attacked all the prey. But in a tube covered with a plastic film that hid light polarization, cuttlefish were more reluctant to attack the shrimp. As they grew older, they got faster at spotting all their victims, but they still didn't like to attack transparent prey unless they could see the polarized light coming off their bodies.

Darmaillacq says newly hatched cuttlefish seem to already have the cognitive skills that make a good hunter, such as learning, attention, and decision making. Her experiments also show that cuttlefish can see light polarization soon after hatching, and that skill helps them find transparent prey and decide when to pounce.

The cuttlefish's colorblindness is a deficit that's almost impossible to believe once you've watched this camouflage master in action. Darmaillacq says the ability to see light polarization may make up for the cuttlefish's missing color vision.

Polarized light helps young cuttlefish spot some of their favorite transparent snacks, which would otherwise be hidden. Additionally, "Wavelengths vary a lot depending on the depth [of the water]," Darmaillacq says. "Light polarization does not." In other words, colors can lie in the ocean, but polarization tells the truth. This means cuttlefish can see well enough that their prey—like the fish in this video from the New England Aquarium—never see them coming.




Cartron, L., Dickel, L., Shashar, N., & Darmaillacq, A. (2013). Maturation of polarization and luminance contrast sensitivities in cuttlefish (Sepia officinalis) Journal of Experimental Biology DOI: 10.1242/jeb.080390

Image: Leonard Clifford (Flickr)

Video: New England Aquarium

12 Days of Inkfish, Day 12: Cuddlefish

Sometimes a cuttlefish wants to cuddle, and sometimes it wants to attack you with its face and ingest you whole. Both sides of the cephalopod's personality are on display in this video from the BBC. Also on display: the giant cuttlefish's unbelievable full-body strobe light effect. This is an animal you want to stay on the good side of.

Thanks for celebrating the 12 Days of Inkfish with me! Next week, regularly scheduled programming will return. Stay tuned for new science and new marveling at nature's old—but spectacular—tricks.

Until then, did you miss any of these?

Day 1: What happens when inkfish receive gifts
Day 2: Life as an upside-down jelly
Day 3: Head explosions and a reverse sun
Day 4: The help desk answers "orangutan stop following me" and other reader questions
Day 5: A video of grebes running on water to prove their commitment
Day 6: How Zion Canyon is like the Princess and the Pea
Day 7: Which posts won Best Mustache and other superlatives in the 2012 yearbook
Day 8: This nebula is a square peg in a round universe, thank goodness
Day 9: These airport worms are hard at work eating your garbage
Day 10: Sending you all on an acoustic scavenger hunt (please report back!)
Day 11: The most charming breeds of purse animals

Image: Screenshot from "Animal mating rituals of giant cuttle fish in the blue Australian ocean waters" by BBC Worldwide

12 Days of Inkfish, Day 1: Gifts

Consider this a big, many-tentacled squeeze from me to you.

This year, I've expanded into new habitats, learned new tricks (like driving the Shambulance), and seen lots of new readers swimming by. I'm grateful to every person who visits and shares these pages. You've given me a reason to learn about wine-making wasps and anti-placebos, to taste no-calorie noodles and verbally abuse sheep. Say hello in the comments!

For each of the 12 days of Christmas I'll be leaving a little something here to unwrap. The first is a video of an octopus receiving a live crab in a jar. After menacing the crustacean briefly, it unscrews the jar's lid and squeezes its whole body inside to devour its prey. Talk about a stocking stuffer.



Video from CBCtv.

Deep-Sea Census Finds Glow-in-the-Dark Bonanza

Sometimes the best way to answer a question like "How many animals on the bottom of the ocean glow?" is to just go down there and poke some sea creatures with a robot arm. That's how researchers found out that the pitch-black seafloor in the Bahamas is alive with bioluminescence. They also found glowing currents full of plankton, a crustacean with the world's slowest vision, and creatures that vomit light when provoked.

In the middle depths of the ocean, making your own light is ordinary. Around 80 percent of fish and crustaceans that live here are bioluminescent, and the skill is also common in squid and other cephalopods. These animals may light up to lure prey, confuse predators, or attract a mate.

Species that live on the bottom of the ocean are less well studied, for the obvious reason that they're on the bottom of the ocean. So researchers led by Sönke Johnsen of Duke University and Tamara Frank of Nova Southeastern University set out to begin a census of bottom-dwellers. They descended in a submersible to the floor of the Bahamas to knock on some doors.

The team made 19 dives to depths between 500 and 1000 meters. Once at the seafloor, they began scooping up samples of all the species they could find, using the submersible's robotic arm. On some of their dives, they turned off the sub's lights and sat in total darkness: they could see life glowing all around them. The researchers tested individual creatures for bioluminescence by gently poking them with the robotic arm. If something glowed in response, they grabbed it or sucked it up for further study.

Bioluminescence, at least in the limited regions the researchers were able to explore in their dives, was rarer than in the middle depths of the ocean. Less than 20 percent of the species they observed could glow. The skill was most common among sea anemones, bamboo corals, and coral relatives called sea pens (so named because some of them look like old quills).

Although the ability to light up was uncommon, the light on the seafloor was abundant, thanks to bioluminescent plankton. Drifts of these tiny animals are carried on the currents and ping with light whenever they collide with another object. "Where there are 'tree-like' animals...that stick up from the bottom," Frank says, "the tiny plankton that flows by in the currents get stuck on it."

The frequent flashing of drifting plankton could be one reason bioluminescence is a less common skill on the seafloor, the authors write. It might not be worthwhile to try to generate bioluminescent signals when the visual noise of plankton is drowning everything else out. Another reason not to bother with bioluminescence on the seafloor could be that the uneven terrain, punctuated by corals and other stationary creatures, blocks signals from traveling far. In the middle of the ocean, light can travel in every direction.

Yet the large eyes on some of the specimens they gathered told the researchers that light was still an important signal for them. When the team brought their subjects back to the surface to photograph them and measure the light they emitted, they found that the stationary animals (such as anemones and corals) gave off a greener light compared to the bluish glow of mid-ocean animals. This might be an adaptation that lets light travel farther through the cloudier water of the ocean floor.

Most of the bioluminescent creatures that Johnsen and Frank observed glowed suddenly when bothered, then faded over the next few seconds. But a few were more creative with their light production: they found a sea pen that pulses with half-second flashes; a bamboo coral made up of polyps that flash individually, creating a twinkling effect; and a shrimp that vomits light in self-defense. ("In the deep dark depth, squirting a blindingly bright fluid into the face of a predator is certainly going to distract it," Frank says, "allowing the spewer to get away.")

When the researchers collected crustaceans from the ocean floor using baited traps, they got even more surprises. One was an isopod with the slowest vision ever recorded in a crustacean. The researchers measured the "flicker rate" of the crustaceans' eyes, which is the number of images the eyes send to the brain every second. In humans it's about 60, which means movies shown a little faster than 60 frames per second look seamless to us. In the crustacean Booralana tricarinata, the flicker rate is just 4.

Gathering only four snapshots of the world each second, the isopod is probably unable to follow the motion of even slow-moving prey. It's possible, the researchers say, that the animal instead uses those slow eyes to scavenge. Its long-exposure vision might let it see the subtle glow of bioluminescent bacteria living on its food. In other words, though it can't see motion, the isopod sees a whole glowing ocean-floor world we'll never be able to.

Sönke Johnsen, Tamara M. Frank, Steven H. D. Haddock, Edith A. Widder, & Charles G. Messing (2012). Light and vision in the deep-sea benthos: I. Bioluminescence at 500–1000m depth in the Bahamian Islands The Journal of Experimental Biology DOI: 10.1242/jeb.072009

Tamara M. Frank, Sönke Johnsen, & Thomas W. Cronin (2012). Light and vision in the deep-sea benthos: II. Vision in deep-sea crustaceans The Journal of Experimental Biology DOI: 10.1242/jeb.072033

Image: Bioluminescent plankton by NOAA (via Wikimedia Commons).

Octopuses Host a Masterclass on Hiding

When you're surrounded by an ocean full of potential predators, the best way to avoid seeing the inside of one's stomach is to make sure none of them see you in the first place. Octopuses and some other cephalopods are experts at camouflage, manipulating the colors and textures of their skin to hide in plain sight. But their strategy, it turns out, has nothing to do with disappearing into the background.

To learn the camouflaging secrets of the masters, researchers led by Noam Josef at Ben-Gurion University of the Negev in Israel went scuba diving. On reefs in the Red Sea and Tyrrhenian Sea, they snapped pictures of two octopus species (Octopus cyanea and O. vulgaris) whenever they saw an individual hiding—crouched low and motionless for a minute or longer.

For the pictures to work in the team's digital image analysis, they had to be sunlit just so and taken from directly above. Over three years, they captured just 11 photos that fit their criteria. "These images are a bit hard to get," Josef said in an email. Not to mention the challenge of finding a camouflaged octopus in the first place.

Hint: Look for the coral with tentacles.

Each bird's-eye, or rather shark's-eye, photo was converted to a grayscale image. Researchers selected a rectangle showing the pattern on the octopus's mantle (the part that's not tentacles). Then a software algorithm compared the mantle sample to rectangles from everywhere else in the photo, shifting the frame one pixel at a time and searching for a match.

The best matches to the octopuses' camouflage patterns were not to be found in the gravelly ground beneath them. Instead, 10 out of the 11 octopuses had clearly mimicked a specific object nearby. They played coral, rock, weird sand blob, or algae patch.

View this picture larger and you'll see that one coral has eyes on top.

A camouflaged animal's best strategy depends on the viewpoint of its predators. Many fish have light-colored bellies that blend in with the sky when seen from below. Certain pygmy sharks take this trick a step further and emit a blue glow from their undersides. When viewed from above, fishes' darker-colored backs vanish into the background of the ocean.

An octopus sitting on a reef has to worry about big fish hunting from above, as well as moray eels and other predators that creep up from the sides. Since these enemies approaching from different angles will see the octopus framed against different backdrops, maybe it makes sense for the octopus to forgo blending in altogether. It's stuck being obvious, so it may as well pose as an obvious object that's less edible.

"Sometimes octopuses make an honest mistake and simply become conspicuous" by camouflaging, Josef says. "However, in a complex environment like the coral reef, acquiring key features of an object may serve the octopus better than just matching the general look of the reef." You can see a few of those convincing key details in the photos above, where octopuses have contorted themselves into the knobby branches of a coral or a shell's striped ridges.

Scientists have discovered some of the specialized cells in octopus skin that help them pull off their elaborate imitations—pigment holders, reflectors, light scatterers. But Josef says there are still more questions than answers: "What visual cues are used by these animals? How do octopuses match their colors even though they're colorblind?" (Yes. Colorblind.) "What information is transmitted from the eye to the brain? And what does an octopus really see?"

We're still "far from understanding" the camouflaging act of the octopus, Josef says. We'll have to keep hunting for scraps of information the cunning cephalopods let slip. That is, assuming we can find them first.

Josef, N., Amodio, P., Fiorito, G., & Shashar, N. (2012). Camouflaging in a Complex Environment—Octopuses Use Specific Features of Their Surroundings for Background Matching PLoS ONE, 7 (5) DOI: 10.1371/journal.pone.0037579

Images: Top, Ms. Keren Levy. Middle and bottom, Mr. Zvika (Ziggy) Livnat.

Blogday Octopus

Thank goodness my office octopus was watching the calendar, or else I would have missed my second blogday entirely.

It's been quite a couple of years. I've stayed up late writing about missing snow and synesthesia; I've gotten up early to search for images of drunken flies, problem-solving crows, and mustached monkeys. I yawned roughly nine thousand times while working on a story about yawning triggers, and ruined two meals working on a piece about placenta eating. I may have covered every breaking news story in the field of poop.

And every day I've been surprised and happy to see you--yes, you--reading, sharing, commenting, liking, tweeting, Stumbling and Digging (the last two are especially appropriate, given my propensity for poop stories). Thank you.

If you want to celebrate with Octopus and me, why not comment on a post sometime? We'd love to hear your voice. Or send a story to a friend! The more the merrier, as I'm pretty sure they say under the ocean. Unless you're a top predator species or something that lives alone under a rock.

Eternal Sunshine of the Spotless Slug

This post first appeared in May 2011. Yes, I'm on vacation for another couple of days and Inkfish is in reruns.

In a creature much simpler than a human, scientists have figured out how to erase a memory. Sea slugs that had received repeated electrical shocks learned to expect them again--until researchers gave the slugs an injection that returned them to blissful ignorance.

The fellow above is Aplysia californica, a hefty sea slug that's shown here releasing its mysterious magenta ink. (I suppose that makes it an honorary inkfish?) Researchers at UCLA used a tankful of these quarter-pound slugs to test the hypothesis that a certain molecule allows the slugs to store long-term memories.

At the beginning of the experiment, researchers tested the slugs' baseline sensitivity by poking them in the hind end with a broom bristle. This causes a slug to retract its siphon, a straw-like structure near the tail, for a second or two. Then they "trained" the slugs by giving them five sets of electrical shocks to the tail over the course of 80 minutes. Afterward, the slugs had learned the lesson that touches near the tail are bad. (Come to think of it, that may have been the title of a movie we watched in my fourth-grade health class). Twenty-four hours after their training session, the slugs still remembered; they retracted their siphons for 40 or 50 seconds when poked with a broom bristle. The reaction was almost as strong 48 hours after the training session.

(Two days may not seem like a very "long term" over which to remember that you were recently tormented by scientists. But short-term memory only refers to the items that we hold in our minds on the order of seconds. Anything we hang on to for longer than that is considered to be in our long-term memory.)

And then it was time for some Men in Black mind-erasing action. The molecule the researchers were interested in is called protein kinase M (PKM). A few minutes after the 24-hour test, they injected some of the sensitized slugs with a molecule that interferes with PKM and prevents it from doing its normal job--which is, in case you asked, adding phosphate groups to other proteins.

The results were straightforward and striking. At 48 hours, when the other slugs were still extremely reactive to being poked in the tail, those that had been injected with the PKM blocker were completely back to normal. Their siphon-retracting reflex was exactly what it had been before their training. The memory of the electric shocks they'd received seemed to be gone.

The scientists even tried reminding some of the slugs of their training. At 96 hours, they gave them one more set of shocks (as opposed to the five sets in the initial trial). The slugs seemed unimpressed, showing no change to their reaction.

In another experiment, the researchers left the slugs alone for a whole week after their initial shock training. On day 7, the slugs were still sensitized from their training, withdrawing their siphons for around 40 seconds when poked. Some of the slugs were injected with a PKM blocker at this point, a whole week after the training session. The next day, those slugs' reactions were right back down to zero. The un-injected slugs, though, still remembered their shocks.

The researchers also experimented on individual slug neurons--one sensory neuron and one siphon-moving neuron--that they removed from the slugs and kept in a dish. Again, they found that blocking PKM prevented the siphon neuron from retaining its "memory."

So what is PKM doing to neurons that makes it so critical to long-term memory? New memories involve the growth of connections between neurons, and the authors think the ongoing activity of PKM might be necessary to maintain these structural changes. Without housekeeping by PKM molecules, the connections are lost.

Researcher David Glanzman, who led the study, believes that understanding these processes could lead, in the future, to targeting and erasing specific memories in humans. "Almost all of the processes that are involved in memory in the snail [or sea slug] also have been shown to be involved in memory in the brains of mammals," he said in a press release.

It's a spooky idea, but erasing memories might be of help in treating post-traumatic stress disorder or drug addiction. The process might even be reversed to treat Alzheimer's disease, which is currently incurable. Let's hope that when that day arrives, someone remembers to thank the humble sea slugs.

Image: Genny Anderson/Wikimedia Commons

Cai, D., Pearce, K., Chen, S., & Glanzman, D. (2011). Protein Kinase M Maintains Long-Term Sensitization and Long-Term Facilitation in Aplysia Journal of Neuroscience, 31 (17), 6421-6431 DOI: 10.1523/JNEUROSCI.4744-10.2011

Interview with an Inkfish

It's Halloween, and I may not be wearing a scary costume, but I have snuck up on the Chimeras blog.

As part of her Author Interviews series, E. E. Giorgi asked me what it's like to write about science for kids (and adults). Click here to read our conversation about junior paleontologists, PCR, and unconvincing threats.

Happy Hiatus!

Hi, friends. I'm going to be away from this space for about a week and a half, so I'm leaving some nibbles to tide you over till I get back.

I thought about listing some "most popular" posts, but, well, you may have read those already. So instead, here are some less-loved posts from the past. Why less loved? Funny story; at the beginning of the summer, there were one-fifth as many of you reading as there are now.* While I'm away, why not share your favorite Inkfish story with a friend, or follow me here or on Twitter?

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Science's Biggest Cancer Questions: What does the National Cancer Institute think are the most pressing unanswered questions about cancer? Featuring obesity, Alzheimer's disease, and sea turtles.

The One Funny Thing: You'd be surprised what shows up in the Methods section.

Little People, Big World: Tricky sensory illusions make you feel like a giant--or a Barbie.

Depression and the Loss of Old Friends (and Worms): An intriguing hypothesis links mental illness to a lack of dirt in our lives.

Woo Hoo, Witchy Woman: I love the New York Times, but sometimes they publish stupid stories about ovulating women in ponytails.

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*Thank you.

Photo: Wikipedia/albert kok

Sneaky Squid Use Custom-Sized Sperm

How big should your sperm be? If you're a squid, it depends where you're putting them.

Males of the species Loligo bleekeri follow one of two mating strategies. Larger males mate with a female in the traditional way (for a squid), depositing packets of their sperm inside her oviduct. They then guard the female to make sure no other males mate with her. Small males, on the other hand, don't bother with the colorful displays that are required to woo and mate with a female. Instead, they dart up to an established squid couple and stick some sperm packets on the female's head.

This may seem futile, but the females of L. bleekeri happen to have a secondary sperm-storage organ near the mouth. The so-called "sneaker" males aim for this receptacle when adding their contribution to the mix. When a female eventually extrudes a string of eggs, it passes by both the internal and external sperm stores before landing on the sea bed. This gives all males involved a chance to father some bouncing baby squid.

A group of researchers in Japan and the United Kingdom, led by Yoko Iwata, collected female and male L. bleekeri squid, including both large and small males. They relieved the males of their sperm packets, called spermatophores, and studied their contents. What they saw was that squid sperm come in two distinct sizes. Large squid have smaller sperm, and small squid have larger sperm. (Before you ask, both varieties are larger than human sperm.) And the two sperm sizes are completely segregated between the two receptacles in a female.

It's the first time a single species has ever been discovered to have two separate sperm types. The squid themselves come in two distinct sizes, too; they seem to be built specifically for one mating strategy or the other. How they develop this way is unknown.

The different sizes of sperm don't seem calibrated for competition with each other, though. In swimming tests, large and small sperm were equally fast. They also were both able to fertilize eggs. The researchers speculate that the different sperm sizes have evolved due to the environments they're left in. Small squid leave their sperm out in the open, where they're more susceptible to being washed away by water. Other factors that differ between the two fertilization environments, "such as salinity, viscosity, pH and concentrations of gases and nutrients," may have influenced the evolution of large and small sperm. Each size of sperm seems to be optimized for the mating strategy it's used in, giving both sizes of squid a fighting chance at fertilization.

Squid are far from the only animals to employ spermatic gamesmanship. Unromantic males of various other species use a "sneaker" strategy. For example, in the European common frog Rana temporaria, a  "pirate" male searches for freshly laid piles of eggs, then deposits his sperm directly onto them. The eggs have already been fertilized once before, as the female released them, by the male who was actually mating with her. But the pirate has a chance to fertilize any eggs in the batch that got missed the first time. To increase his odds, he sometimes crawls bodily into the egg mass before doing the deed.

Other species use a "copulatory plug," a sticky mass left in the female after mating to prevent other males' sperm from getting in. This is a popular strategy that shows up in species ranging from bumblebees to snakes to squirrels to monkeys. Males of the orb-weaver spider Nephila komaci, not messing around, break off their genitalia in the female to serve as a plug. The male black-winged damselfly has a penis shaped like a scrub brush, which he uses to scrub away his rivals' sperm. In an especially creative adaptation, some rodents produce hooked sperm that join together in transit to form (this is an actual scientific term) sperm trains.

Sperm competition is a high-stakes game; it's the difference between passing on your genes and not. Females, whose only directive is to find the fittest male to fertilize her eggs (if she gets any choice in the matter), don't face nearly the same evolutionary arms race. I'm sure that's some consolation to the female L. bleekeri, drifting through the ocean with sperm packets glued all over her head.

Iwata, Y., Shaw, P., Fujiwara, E., Shiba, K., Kakiuchi, Y., & Hirohashi, N. (2011). Why small males have big sperm: dimorphic squid sperm linked to alternative mating behaviours BMC Evolutionary Biology, 11 (1) DOI: 10.1186/1471-2148-11-236

To Visualize Dinosaurs, Scientists Try Paint-by-Numbers

Now that we know some dinosaurs had down or feathers instead of the scales we used to imagine, there are intriguing new questions to be answered. Did forest-dwelling species use patterned feathers for camouflage? Did other dinosaurs use flashy colors for communication or courtship, like modern birds do? Using new imaging techniques, scientists are beginning to color in their dinosaur outlines. 

In previous studies, researchers have scoured fossils of dinosaurs and early birds for melanosomes, structures in cells that hold the pigment melanin. (Despite the range of colors in our eyes, fur, and skin, most animals only produce one pigment: the brownish melanin. Blues and greens can be created by light-scattering tricks.) The shape of a melanosome can tell researchers what type of color it was responsible for, from black to yellow to red. But melanosomes, like other non-bony structures, break down over time and are hard to find in fossil form. 

Instead of searching for the cellular packages that held pigments, Roy Wogelius and other scientists at the University of Manchester decided to search for traces of metals. Elements such as copper, zinc, and calcium bind to melanin while an animal is alive. Though the melanin decays over time, the metals remain behind.

The researchers used a new imaging technique that's sensitive enough to find and map trace distributions of elements. They first scanned samples from non-extinct species, including a fish eye, bird feathers, and a squid. The distribution of copper turned out to correspond with the most pigmented areas in the animals--the squid's ink sac, for example, was highly coppery.

Then Wogelius and his colleagues turned their scanners to fossils, including Confuciusornis sanctus, an early bird that lived with the dinosaurs. (Confuciusornis was discovered in China and named after who you'd think.) The researchers created a map of copper distribution in the fossil, which you can see below. Copper is shown in red. 

Based on their map, they could then sketch a shaded-in Confuciusornis.

This technique doesn't yet tell us what colors Confuciusornis wore, only where its darkest feathers were. Those areas could have been black or brown or red--or the bird could have colored its feathers through its diet, as a goldfinch or a cardinal does today. Since that kind of coloration doesn't involve melanin, it would be invisible to these scans. But as technology improves and becomes more sensitive to the microscopic tidbits of information hidden in fossils, we may be able to find out what dinosaurs really looked like. We might be able to discard the green and brown lizards plodding through today's books, like the sepia-toned photographs of the past, with something much more lifelike. 

Wogelius, R., Manning, P., Barden, H., Edwards, N., Webb, S., Sellers, W., Taylor, K., Larson, P., Dodson, P., You, H., Da-qing, L., & Bergmann, U. (2011). Trace Metals as Biomarkers for Eumelanin Pigment in the Fossil Record Science DOI: 10.1126/science.1205748

Cephalopods Not in Space

After 15 days in orbit, the crew of the space shuttle Endeavour will be returning to solid ground tomorrow. Their mission has been notable for several reasons: It's the second-to-last NASA space shuttle mission ever, and the last trip Endeavour will take before heading to its retirement home in a Los Angeles museum. The commander of the mission is Mark Kelly, husband of almost-assassinated Arizona congresswoman Gabrielle Giffords. The shuttle's crew successfully delivered the Alpha Magnetic Spectrometer (AMS), an extremely expensive piece of particle physics equipment, to the International Space Station.

And, of course, there are some squid on board. I wrote earlier about Squids in Space, a project to study whether friendly, glowing bacteria that live inside squid behave badly in a low-gravity environment.

I also asked you all to go to YouTube and vote for a question I'd submitted for the PBS News Hour's "You Talk to Endeavour" interview. There were more than 1,800 questions submitted by the public. My question was about the future: What will it mean to be an astronaut in 25 years or so, when today's teen space fanatics have joined the space program? I was hoping to use the answer in my magazine, and I got enough votes to stay near the top of the pack (thank you!). The interview took place on May 19. Hi, astronauts!

I think being in space gives people a slightly jolly appearance, since their cheeks float up into their faces a little bit.

Sadly, PBS science correspondent Miles O'Brien--yes, like the Star Trek character--didn't include my question in his interview with the Endeavour crew. But he did have a nice conversation with the astronauts about the Mississippi River (they could see the floodwaters), Gabby Giffords (she watched the launch), and personal trinkets the astronauts take into space. 

He also asked the astronauts to do a group somersault. Judging by the speed with which they complied--the question was barely out of O'Brien's mouth before Mark Kelly went heels-over-head--I suspect they've practiced.

They may as well live it up now. Gravity returns tomorrow, along with the reality of the shuttle fleet's retirement. But the science experiments the crew helped with will carry on without them, including the AMS's cosmic-ray measuring and whatever happened to those squid. As for NASA, we'll see where it heads next.

Images: Google/PBS NewsHour/YouTube

Shine for the Camera!

Images of the earth at night may strike you as beautiful (if you're someone with a penchant for satellite photos) or distressing (if you're concerned about the effect of light pollution on migrating animals and/or you're a sea turtle). Some economists look at these photos and see tools for gathering data about other countries.

Previous research has found that luminosity--how much light a geographic area gives off at night--is a kind of shorthand for that area's economic productivity. Countries with a higher GDP (gross domestic product) have more stores that stay open at night, more cars on the road, and more electric lights guiding their citizens. More light means more business.

A new study by Yale economists Xi Chen and William Nordhaus asks just how useful this shorthand is. Can we use satellite photos to estimate the GDP of countries that don't collect or give out economic data? Haiti is one such country, lacking the resources for things like census collection. (You can see the clear dividing line in luminosity between Haiti and the Dominican Republic in the picture below. Puerto Rico is the well-lit island all the way to the east.)

The researchers used satellite images taken between 1992 and 2008. One benefit of these data is that they consist of very high-resolution images, even though the satellites that took the pictures were actually studying cloud cover.

Looking both at entire countries and at smaller regions within countries, the authors created detailed measurements of luminosity and compared them to economic data. They found that looking at nighttime lights was, in fact, useful--under certain circumstances.

For countries that already provide plenty of economic data, luminosity doesn't add much to our understanding. And for countries with extremely low luminosity, there's not enough data to go on. But in general, for countries that don't share much information with us, nighttime lights can serve as a consistent proxy for economic productivity.

(North Korea, a country that certainly doesn't share much information with the outside world, is on the west side of the picture. It's the almost shockingly black space below China and above South Korea. Japan, all the way on the east, is bustling and bright.)

The study is a neat example of how much can be learned just by looking. It also demonstrates how resourceful researchers can use already-existing data sets to generate new information. When economists can use pictures from a cloud-measuring satellite to gather GDP data about other countries--instead of starting a new research project--it means we can save a bit of our own GDP for something else. 

UPDATE: In the comments, Shelby asked about those swirling lights between Korea and Japan. They didn't seem to be related to shipping, since the lights don't follow direct paths. I took a quick spin around the globe on Google Earth and didn't find the same light patterns anywhere else. But an internet search turned up the answer: squid fishing (the link is a PDF), which is an especially large industry in Japan. Fishermen work at night and use powerful lights to attract the squid. It all comes back to inkfish!

Images: Google Earth