Cross-Dressing Cuttlefish Puts on World’s Most Spectacular Light Show

Before we had the luxuries of modern science, folks used to believe that every land animal had a counterpart in the sea. So in the depths there naturally must be sea cows, sea unicorns, and even sea pigs. By that logic, there must also be sea humans, and if we’re going to get specific, I’d like to nominate a sea hipster: the cuttlefish, a creature with immaculate fashion sense whose ink we’ve long used to make sepia-toned photos, which is totally retro right now.

These are far and away nature’s most adept camouflagers, capable of observing their surroundings and perfectly adjusting not only their color but also their skin texture in just 250 milliseconds (one species is so clever, in fact, that males can brilliantly imitate females for a chance to mate — it’s complicated). But this isn’t just about blending in: They can also launch truly bizarre displays of rippling colors to either intimidate rivals or hypnotize prey. Oh, also. They’re color blind. Yeah … scientists aren’t quite sure how that’s possible quite yet.

These are voracious, exceedingly clever predators of the highest order that aquariums have struggled for decades to raise in captivity, to no avail. Until now. Opening tomorrow is the Monterey Bay Aquarium’s Tentacles exhibit in California, a showcase of the most remarkable cephalopods from around the world, including the charming cuttlefish.

Their marine biologists have finally learned how to raise many cuttlefish species through their entire life cycle — from birth to successful reproduction — including the flamboyant cuttlefish, a teeny tiny wonder with poisonous flesh that “walks” along the seafloor and fires an incredible display of rippling zebra stripes, shown in the video below. If you have the means, get to the Monterey Bay Aquarium to see them in all their glory. And try the margherita pizza from the cafeteria. It ain’t half bad.

It Puts the Commotion on the Skin

I’ll get to the aquarium’s tactics in a bit (with raising cuttlefish, not making pizza), but first a profile of this astounding creature is in order. There are over 100 species of cuttlefish living in reefs all over the world, save for North America, one of the many reasons it’s such a treat to have them at the Monterey Bay Aquarium.

The cuttlefish’s most striking feature, of course, is its rapidly camouflaging skin, which is separated into three layers. The first is composed of pigmented chromatophores, some 200 per square millimeter, which open and close with tiny muscles to reveal yellow, red, and brown, or slight variations of those colors.

The second layer is made up of structural reflectors, which bounce light to give off a sort of iridescence. “They provide many colors,” said Roger Hanlon, a marine biologist at Brown University, “but especially the blues and greens, the short wavelengths or cold colors, thus complementing the chromatophores, which produce the warm, long wavelength colors. And so together those two layers give you all the colors of the rainbow.”

Finally, below this is a bottom-most layer of solid, unchanging white, which the cuttlefish can expose to produce high contrasts against the vivid colors of the chromatophores. Working in concert, these layers allow the cuttlefish to put on nature’s most dazzling light show, blowing all those flashy bioluminescent creatures of the deep out of the water, so to speak. And it’s all powered by one of the biggest brains relative to body size among invertebrates.

“One of the things that they’ve done very well is color coordination with the background, and that’s great, but how do they control that?” Hanlon asked. “Well it turns out they’re color blind. So how do they achieve color-blind camouflage? It’s one of those vexing questions that we’re still trying to figure out.”

And the cuttlefish doesn’t stop at color: It can also morph its skin with 3-D projections called papillae. “They’re like the ultimate goosebumps, I suppose, if you want a weak human analogy,” said Hanlon. “So to complete the picture of really perfect camouflage, they not only have the optical color, pattern, and contrast worked out, but they also have the three-dimensional skin texture worked out. And it’s the only animal on the planet that can control that.”

The cuttlefish can match the colors and patterns and textures of virtually any background, including, it seems, man-made ones like checkers in the video above, just in case it finds itself inside a shipwrecked freighter that was carrying board games. Incredibly, though, Hanlon has found that the cuttlefish doesn’t have hundreds of camouflage patterns ready to deploy. Instead, it’s working with just three templates, which it proceeds to customize with different hues and textures given the environment.

Eat Prey, Love

But why evolve skin that sucks up not only a huge amount of brain power, but also energy? Remember that muscles are controlling the thousands upon thousands of chromatophores.

A giant Australian cuttlefish in its Sunday best, which it wears to the Church of Marine Vegetation.

“What drives it is extreme predation pressure by the best visual systems on the planet, mainly in the form of what we call teleost — or bony — fishes,” said Hanlon. “So think of any predatory fish, game fish, everything from tuna to jacks to barracuda to groupers, all these teleost fishes that have developed a wide variety of keen visual capabilities.”

The cuttlefish evolved from an ancestor with a shell — which its relative the ancient nautilus retains to this day — finding itself soft-bodied and smack in the middle of the food chain, not an ideal place if you’re interested in, you know, survival. So eluding prey became a high-stakes game of hide-and-seek, with the best camouflagers surviving to pass along their good genes. Over countless generations (cuttlefish don’t live longer than two years, so we’re talking rapid turnover here), they evolved into the flashy, big-brained wonders we know today.

But don’t be mistaken: The cuttlefish isn’t spending its days cowering in the substrate. It’s a fearsome hunter itself, equipped with powerful peepers, whose bizarre W-shape Hanlon reckons gives the cuttlefish an advantage in looking upward.

“Remember, their eyes are where our ears are,” said Hanlon. “Their eyes are not binocular vision, except when they’re approaching a prey organism. They’ll scrunch the eyes forward so they have stereopsis to determine the distance away from the prey that is about the length of the tentacles.”

Now, cuttlefish keep these two tentacles retracted in a pocket amidst their eight other arms. When they reach striking distance, they flare out their arms, momentarily blinding themselves as they fire the tentacles at the prey. In a split second, these toothed suckers slam into the critter, and the cuttlefish reels in its quarry to the gnarly beak that is its mouth.


 Using its eight arms to hold fast to, say, a fish, the cuttlefish first bites through the back of the head, paralyzing the prey. It can even chew through a crab’s shell “and inject a neurotoxin that’ll slow down the central nervous system,” said Hanlon. “They essentially paralyze the crab in less than a minute.” In this way, they can take prey their own size, holding on tight and leisurely munching away.

Cuttlefish have huge appetites, frantically fueling not only their big brains and dazzling skin, but also their rapid growth. And when you mate like a cuttlefish does, you’re going to want all the mass you can get. Or you can just cross-dress.

Something Fishy Is Going on Here

The giant Australian cuttlefish is indeed giant, growing to three feet long, though it’s not technically Australian, on account of lacking the proper citizenship papers. At the peak of the spawning season, there are as many as 11 males to every female, according to Hanlon. That’s a lot of competition. The largest males are best equipped to claim a female and easily fight off smaller challengers, but small males have a clever strategy for wooing ladies.

After several unsuccessful attempts of squirming past the big fellas, they’ll actually change their color to match that of a female. Males will also modify their fourth arms, which are larger than those of the females. “What these little guys do is they pull their fourth arms up, they retract them up and they make them look smaller like a female’s fourth arms,” said Hanlon. “And then they bulge their arms up as if they’re holding an egg.”

When females are holding an egg, you see, they’re never receptive to mating. So not only does the dominant male see a female instead of a male, he sees a female he has no chance of getting busy with. The little impostor slips by unnoticed and surreptitiously mates with the female. (This is not unlike the classic Marilyn Monroe flick Some Like It Hot, in which Tony Curtis and Jack Lemmon think that cross-dressing will bring them closer to that legendary beauty. Scientists aren’t yet sure, though, whether some cuttlefish also like it hot.)

“Then the question is, why did the female accept that sneaky little male and mate with him?” asks Hanlon. “Overall, females are very choosy and they reject 70 percent of mating attempts on them, but the little guys who morph into a female and waltz in there, they only get rejected 35 percent of the time.”



But how could the dominant male be so gullible? He’d just finished chasing the little jerk around for a half hour, and all of a sudden his foe tweaks his body a bit and boom, threat removed? For Hanlon, this could be due to the cuttlefish’s solitary nature. It doesn’t have the well-developed skills required to make such social recognition possible — at least not yet. “Maybe in another 1,000 generations that won’t work any longer,” he said, “but right now it’s fine, thank you very much.”

Cuttlefish mating happens face-to-face, with the pair entangling arms. The male reaches down with his enlarged fourth right arm and grabs sperm packets called spermatophores, which he’ll crack open on the female. The sperm then ideally make their way into two little pouches inside her, known as seminal receptacles, for her to store and access at a later time. The two separate, and she’s ready to mate with the next male.

“And the females always — every time we’ve done a study — always have different sources of sperm from different males,” says Hanlon. “So they’re playing a statistical game to diversify their portfolio, if you will, to get sperm sources from different males, hoping to get a range of fitness among those males to increase their own eggs for fertilizing and reproducing in the next generation.”

Strangely, females actually have a choice over which sperm to use after the male is long gone. How exactly she’s able to do so, scientists aren’t quite sure. “It’s called cryptic female choice, which is a delightful term,” Hanlon said. “It’s cryptic to the male, he doesn’t know what’s going on, but she’s doing some manipulation of sperm. So it’s a pretty dynamic mating system, lots of clever behaviors.”

Not Getting Cuttlefish Juiced Up on Caffeine, and Other Adventures in Aquarium Science

The cuttlefish’s strange sex life is but one of many mysteries that have vexed aquariums trying to raise these creatures in captivity. Just ask Bret Grasse, a marine biologist at the Monterey Bay Aquarium, who helped pioneer the techniques to not only raise cuttlefish with unprecedented success, but to be so successful that they’re shipping their extra specimens to aquariums around the world.

Cuttlefish eggs incubating in soda bottles is the only recorded instance in history of a soft drink actually saving a life instead of shortening it.

 Forget about the diminutive young virtually disappearing with their exceedingly good camouflage. Forget that cuttlefish, not exactly accustomed to walls in their homes on the high seas, can sometimes slam into tank walls and fracture their cuttlebone, the thin structure of calcium carbonate that gives the creatures their buoyancy — a problem the aquarium solved, by the way, with tanks padded in plastic. You also have to somehow get a highly antisocial animal to play nice with its new roommates (I smell a sitcom).

“There are certain instances of cannibalism, and a social hierarchy develops as they grow older, too,” said Grasse, “where larger ones will start killing the smaller ones. Or based on your gender ratio, you’ll have either successful pairings with the right male to female ratio or you can have a big disaster on your hands based on that too.”

But first you have to get them to hatch. Surely one of the more inventive homebrew techniques at the aquarium is the soda bottle incubator, a device that’s orders of magnitude cheaper than commercial models.

In the wild, cuttlefish eggs require constant attention from their mother, who blows water over them to supply a steady stream of oxygen and keep algae from gaining a foothold. Instead of allowing the mother to instinctually care for her young like this, Grasse removes the eggs and drops them in an aerated soda bottle — without the soda, of course. These hyperactive critters are the last creatures on Earth you’d want going manic on caffeine.

“What that does is it takes away that maternal duty by the mother cuttlefish,” he said, “and allows her to reallocate that energy into oviposition and just basically making more eggs.” Using this technique, the aquarium went from having 35 percent of their pharaoh cuttlefish eggs actually hatch to an incredible 95 percent.

Read more at Wired Science