Mesmerizing Marine Mimics: Decoys of the Deep

This post is the fourth in a six post series outlining the evolution of mimicry within the ocean realm. These posts detail various ways in which organisms may copy other organisms in appearance and behavior, and the evolutionary context for how these mimic-model pairings have come to be. The first entry in this series goes over some fundamental introductory concepts and definitions regarding mimicry in general.

Up until this point in this post sequence on mimicry in ocean ecosystems, there has been a focus on examples of animals that have evolved to strongly resemble another species, entirely and completely, in regards to appearance and behavior. But not every mimic goes for copying the whole shebang. Sometimes, just mimicking a specific body part of another creature is all you need to get the job done. Or maybe a tiny portion of your own body is sufficient to parrot the entire visage of a smaller species. I like to call this particular flavor of deception “fractional mimicry”, because instead of whole organisms mimicking other whole organisms, it is organisms mimicking other organisms that are in radically different size classes, necessitating evolutionarily ingenious use of specific regions of the body, or the resemblance of such regions. Fractional mimicry works through the broad manipulation of shape and color, and more importantly, the perception of shape and color in other organisms. I’ve already talked about a species that uses fractional mimicry earlier in this post series; the mimic octopus, which can use a subset of its tentacles to mimic a sea snake, or poke just its stalked peepers out of the sand to mimic a partially buried mantis shrimp. In the same blog post, I talk about a jawfish that is likely mimicking the tip of one of the tentacles of the mimic octopus, following the octopus closely as it moves across the ocean floor: this situation is an example of “fractional mimicry” as I’ve defined it, as the whole body of the fish is used to imitate a small portion of the entire octopus.

There isn’t any significant difference, from an evolutionary or general biological standpoint, between “fractional mimicry” and any other form of mimicry. To be honest, I just needed a good way to break up all of these posts. Grouping together species that share “fractional mimicry” or share the distinction of being fish mimicking invertebrates, or whatever, just makes my life easier. Sorry if that’s a bit of a disappointment.

So, let’s get to talking about “fractional mimics”; animals that achieve all the deception, but with half the work.

This fetching little fish is the comet (Calloplesiops altivelis), although due to its showy, expansive fins, it is also referred to as the “marine betta” (especially in the aquarium trade). It is found on tropical coral reefs across much of the Indo-Pacific, and shares its genus with one other less widely-known species. The comet is a type of longfin (family Plesiopidae), a group of small, predatory, vaguely grouper-like fish somewhat closely related to damselfishes (in regards to damselfish, think clownfish, like Nemo from Finding Nemo). They are also thought to be cleverly subtle mimics. ‘Of what?’, you may ask. A sensible, spotted handkerchief? A floating cutout of a Lite-Brite?

In reality, the likely model for the comet’s mimicry is a living critter, with a lot more in the way of bones, and eyes, and skin. And teeth. Lots and lots of teeth.


Those are some eely nice spots you got there! *nervous underwater laughter*

That distinguished, maculated fellow up there with the thousand-yard stare is a moray eel, in particular, a turkey moray (Gymnothorax meleagris). This species is found all over the tropical Indo-Pacific, and has a range that overlaps significantly with the comet. If you are going back and forth between photos and squinting at each, not entirely convinced that the comet, with all its disjointed, dangly fins, looks anything like a turkey moray outside of the spots, consider that the comet can throw out some remarkable acting chops in a pinch. When startled, the comet has a habit of straightening its larger fins, placing all of their edges together to eliminate gaps, and gives itself a diamond shape. It also takes its pelvic fins (the thin ones that hang below from the front) and tucks them at its sides, enhancing its new arrow shape. The comet then pokes its noggin into a hole in the reef, leaving its tail end out and exposed, conspicuous “eye” spot in full view. When it does this, the comet looks less like Chicken of the Sea and more like something much, much less appetizing.


I haven’t seen a 180-degree turn around this effective since Robert Downey Jr.’s post-rehab acting career.

It is thought that this unique behavior, combined with the comet’s bizarre shape and coloration, is indicative of mimicry of the head of a turkey moray, which wouldn’t be much of a stretch considering how often morays sit motionless in their holes, their heads poking out so they can keep an eye out on the rest of the reef like a bored, nosy, suburban neighbor. I’m calling this “fractional mimicry” because the comet would only be mimicking the commonly exposed head of the moray, not bothering with the rest of the body. This would also be an example of Batesian mimicry, where an organism passes itself off as a more dangerous or distasteful species.

And morays are most definitely an appropriately dangerous model for a mimic to emulate. Moray eels have an unsavory reputation among many divers as extremely aggressive death-noodles crafted directly from the barbarity and hatred of Poseidon himself, full of scorn towards the folly of Man. While tales of their unbridled rage towards all human parts soft and defenseless are a bit overblown, moray eels will bite when provoked or frightened…which usually happens when divers or snorkelers unwisely stick their hands and arms down what they think are empty holes and crevices in the reef. Morays are typically content to stay the fuck away from big, intimidating oddities like ourselves…granted we reciprocate respect of their bubble of personal space. With moray eels, encounters of the “tactile” kind are a recipe for trouble for humans and marine life alike…which is why the popularity of misleading videos like this that show anomalously tame morays acting like eager puppies begging for food and scritches concerns me; “playing” with almost all morays in the real world will invariably end in bloody disaster.

That “bloody disaster” comes directly from the moray eel’s fang-studded bite, the ferocity of which is, unlike their nasty demeanor, not at all exaggerated. While some species have flat, strong chompers that have evolved to crush hard-shelled prey like crustaceans and mollusks, many are ambush predators of fish, rocketing out of hiding spots in the reef and nabbing prey on the fly like that giant penis space slug in The Empire Strikes Back. Fish are particularly hard to hold onto if you don’t have hands, so these morays have mouths filled to the brim with long, sharp, recurved fangs that do a damned good job of holding their wriggling dinner in place. These teeth are also great at doing a shitload of damage to anything that isn’t food…like a human hand. Yanking the deeply embedded eatin’-end of moray eel off yourself causes those fish hooks to run through your flesh like a tractor ploughing furrows in a field. The end result is lots and lots of stitches, if you’re lucky. Google Image search “moray bite” if you have the stomach for photos of hands reduced to nothing but tattered, scarlet ribbons.
Moray eels have even more teeth on a pair of second fucking jaws that lurk further down their throat. These “pharyngeal jaws” are modified gill arches that shoot forward after a fish is snared with the upstream jaws and help drag the hapless victim down into Stomach Town. These marvelous evolutionary inventions only come into play during feeding time, not defensive measures, but any animal with a mouth within a mouth, like an honest-to-Christ Xenomorph, should still be kept at a safe distance.

These predators, with their bites-of-mass-destruction, command a great deal of fearful respect among coral reef animals big and small. Thus, it would make sense if the comet has evolved to mimic the most dangerous end of a turkey moray eel in times of panic.

However, it’s possible the comet may not necessarily be directly mimicking a specific variety of moray, or even morays at all. The position of the fake “eye” spot towards the rear of the body may confuse predators as to where the head of the comet actually is located. For reasons that should be obvious, a bite to the tail region is far easier to survive than a bite to the face, and there is precedence in organisms that appear to use a secondary “fake head” to deceive attackers (an example that comes to mind is Australia’s shingleback skink, a turd-shaped lizard with a tail shaped closely like its head).
The utility of the “second head” strategy may actually extend to the comet’s own predatory habits. Comets slowly stalk their prey, incrementally edging closer, often turning on their side, waiting until the prey item makes a critical avoidance error. Then, the comet lunges, mouth open, at extreme speed. The “eye” marking may be useful in tricking prey, letting the target think the harmful end of the comet is further away than it truthfully is, allowing for a much closer (and successful) approach/seizure.

When one part of an organism’s body is used to mimic another part of the same body, as would be the case in the comet and its “second head”, this is called “automimicry”….loosely, mimicry of one’s self. Many times, this is used to deflect the advances of predators, either by confusing the hell out of them on where they should even attack, or straight-up scaring the everloving fuck out of them. On land, there are plenty of examples of automimicry. Northern pygmy owls (Glaucidium gnoma) have eyespots on the back of their head that give predators the impression that they are being stared down with all the silent malice of a disapproving mother-in-law. Automeris moths have huge, menacing “eye” patterns on their wings that can flashed at predators, making the moth appear to be a much bigger, much more dangerous animal than it actually is, potentially giving the predator pause, and opening up a chance for the moth to escape. Other examples abound, in particular among the more vulnerable groups of winged insects.

An example of automimicry in the ocean comes from the appropriately-named four-eyed butterflyfish (Chaetodon capistratus), a name that is markedly descriptive, yet sounds like a school-ground insult of generations past.


“*snort* Nice glasses, dweeb.”

The four-eyed butterflyfish, native to the warm waters of the Caribbean and West Atlantic, isn’t, of course, actually bespectacled, or the proud owner of a second set of eyes. On either side of the base of its tail is a large, black, white-ringed blotch that resembles one half of a pair of eyes. When alarmed, the butterflyfish promptly turns its ass towards whatever spooked it, and gets the fuck out of Dodge in the opposite direction. It’s thought that these “eyes” mess with a would-be predator’s head, seeing as how many predators aim for the eyes and head when making a kill. It’s possible this would allow the four-eyed butterflyfish to outmaneuver its pursuer in an underwater chase, since the predator wouldn’t be totally sure which direction the butterflyfish would dart, disrupting all ability to predict where to aim and lunge forward.

It’s one thing to use your Mystique-ian powers of shape-shifting, visual deception to lull prey into a sense of false security, or to scare off attackers with an intimidating facade ala those plastic owl decoys used to strike dread in the hearts of obnoxiously-loud, frequently-shitting songbirds….but it’s another thing to use mimicry to get your food to deliver itself straight to your mouth…..

——————————————————————————————————————

Dusk is settling on the reef, and you, a small reef fish, are beginning to stir. Your nocturnal habits have demanded you stay huddled with your school under a coral overhang for much of the day, but as night approaches, you flit about, anxious to venture out into the dark and feed. The blackness grows still, and it feels like a warm and familiar friend. Before long, you’ve decided you’ve waited enough, and you cautiously dart out into the open, your senses trained on your surroundings for any sign of food. You rise up in the water to scan a coral head for food.
Suddenly, you spot something with your huge, saucer eyes, your vision keen in the low light. Movement. You stop, waiting for the motion to once again reveal itself. Again, not far from you, perched high up on a rounded lobe of coral, a sign of movement, confirmed by your sensitive lateral line system, which detects minute vibrations moving through the water. You carefully approach. It wriggles side to side once more. It’s a fish! Your tiny, sesame seed-sized heart quickens its pace in excitement. Your unblinking gaze locks on the fish as it wriggles again. It doesn’t seem to notice you, rhythmically worming in place, nearly resting atop the coral head.
You slowly drift closer. It’s just small enough to fit in your mouth (which, notably, takes up about a quarter of your entire body)…which means its small enough to be a meal. If you’d had salivary glands, your mouth would be watering right now. You get even closer, close enough to pick out its red and yellow colors in the dark. It still doesn’t see you! Your heart races in anticipation. This is going to be too easy! You slowly angle your head towards its beady black eyes. You inch forward ever so carefully, readying yourself to strike. Your mouth is damn near touching its face. In your tiny fish brain, time slows, and you begin counting down your attack. Three. The muscles in your jaw flex. Two. Your gills beat one last time. One.
Then, out of nowhere, the fish’s writhing body goes as rigid as a balance beam. Before you can process what you’ve seen, you feel a terrible rush around you, and blinding pressure and pain on either side of your body. You panic, beating your muscular tail with everything your body has, but you stay in place, your head enveloped in suffocating membranes, and your flanks clamped in place with a vice-like grip. For several seconds you thrash wildly, and as soon as you stop, you feel whatever has captured you flex, and you get sucked deeper. It’s darker than you’ve ever experienced in here. You can’t breathe, and soon, you fade into your gastric tomb.

——————————————————————————————————————

Were you a more intellectually-gifted animal, your last moments would have been full of realization that it was no delectable fish that you had pursued, and that you had been deceived into your death. You had the misfortune of having met your life’s end in the hungry, patient maw of the decoy scorpionfish (Iracundus signifer), lured in by the promise of sustenance.

By and large, the decoy scorpionfish is pretty normal by scorpionfish standards. Scorpionfish (family Scorpaenidae) are a very large and diverse group of fish, mostly made up of ambush predators that lie in wait for prey on the ocean or reef bottom. Most scorpionfish spend most of their lives not moving, attempting to blend in with their surroundings. Smaller fish or crustaceans that stray too close are sucked into their huge mouths through the vacuum caused when scorpionfish open their mouth faster than you or I can even see. Many species of scorpionfish also have potently venomous spines on their dorsal, pelvic, and anal fins, which are, as you can imagine, incredibly useful defensive weapons. A famous, and slightly more ambulatory representative of this group is the beautiful, highly-venomous, and notably invasive lionfish (Pterois). A closely-related family, the stonefishes and ghoulfishes (Synanceiidae), as a group, are the most venomous fish in the world, with some species with stings implicated in human deaths. Like its relatives, the decoy scorpionfish, found on reefs all over the Indo-Pacific, is a bottom-dwelling, stagnant, patient predator, adorned with venomous prickles along its back, a set of lightning-fast jaws, and a face only a mother could love.


Pictured: The deadliest strawberry-and-creme dessert on the reef

What makes the decoy scorpionfish unique among its brethren is that weird band of yellow stretching across the webbing on its dorsal fin. While it looks like a traffic safety reflector, or like someone recently assaulted the fish with a highlighter, its purpose is far more devious.

That little orange and yellow streak is a lure for attracting small, predatory fish to right above that big ol’ ravenous Dyson of a mouth. Lots of other fish use lures to convince prey to come closer. A good example are frogfish and anglerfish (order Lophiiformes), which use vaguely wormy bits of flesh that they jiggle frantically like we would a piece of yarn in front of a cat. However, the decoy scorpionfish’s lure is way, way more sophisticated than the glorified skin tag nightcrawlers used by anglerfish. What do I mean? Well, take a closer look at that front dorsal fin; the part that sticks up like the mast and sail of a ship.


Photo: John E. Randall

How about now? No? That’s fine, I have a video:

Yeah. That lure, with its little “eyes” and “mouth” looks exactly like a small fish. The spine sticking up in the middle even looks like a goddamn dorsal fin! This is no half-assed bit of glowy, spaghetti jigger bait that just keys in on and exploits the stimulus response of prey fish. This lure looks like it was handpainted in an artisanal studio, and is equipped with markings that imitate the body and head of a fish in side view with mindblowing accuracy. The ruse is made all the more powerful by how the decoy scorpionfish broadcasts the presence of the lure. When luring prey, the black “eye” expands slightly in size, and the scorpionfish makes the “fish” “swim” by snapping the first two dorsal spines side to side. This makes the membrane-bound spines further back do “the Wave”, which mimics the wriggling tail and body movements of a fish. This is more than sufficient to garner the curiosity of hungry passersby. All they have to do is get a little too close….and then….WHAM! Sucked down the gullet in one or two gulps. Curtains. Grim Reaper. A locker belonging to a Mr. Davy Jones. You get the idea.

The decoy scorpionfish uses a form of “fractional mimicry” in the reverse sense of the comet, where a small portion of its body resembles the whole body of another animal, rather than the other way around. This is also a case of “aggressive mimicry”, which is sort of the inverse, in a way, from Batesian mimicry; the mimic looks either falsely harmless or enticing, rather than falsely dangerous or off-putting, assisting predation or other types of interactions that benefit the liar at the expense of the sucker. An example of aggressive mimicry that is incredibly similar to the tactics used by the decoy scorpionfish comes from Lampsilis mussels, which use an exceptionally convincing fish-shaped lure to draw larger, predatory bass in close, facilitating parasitism of their clueless target.

This post series will continue: Part 5 will focus on fish that use mimicry to engage in some of the most manipulative, sociopathic behavior under the ocean….

Image credits: Intro image of butterflyfish, comet, turkey moray, comet in defensive position, four-eyed butterflyfish, decoy scorpionfish #1

© Jacob Buehler and “Shit You Didn’t Know About Biology”, 2012-2015. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jacob Buehler and “Shit You Didn’t Know About Biology” with appropriate and specific direction to the original content.

 

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2 thoughts on “Mesmerizing Marine Mimics: Decoys of the Deep

  1. Pingback: Mesmerizing Marine Mimics: Wolves in Sheep’s Clothing | Shit You Didn't Know About Biology

  2. Pingback: Mesmerizing Marine Mimics: Ichthyo-invisible | Shit You Didn't Know About Biology

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