Wondering about mimics?

I have been meaning to write a blog about the Mimic octopus (Thaumoctopus mimicus) and Wunderpus (Wunderpus photogenicus) for ages, but inspiration has eluded me until I was revisiting some of my earlier research on charismatic muck dive species. Both the mimic octopus and the wunderpus are very popular with critter enthusiasts, but we know surprisingly little about them. Time to change that or at the very least tell you some of the things we know about them!

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A wunderpus (Wunderpus photogenicus) checks out my camera

If you’re not a diver or you have never heard of them, the Mimic and the Wunderpus are very (very!) funky species of octopus. They have a wide range of interesting behaviour, they look amazing, and both are found on sandy habitats in the tropics. What they also have in common is that both were only recognised as new species fairly recently (2005 and 2006).

Just by reading their scientific names you could imagine these are not your average cephalopod. The wunderpus’ species name “Wunderpus photogenicus” says it all and  is probably also one of the easiest scientific names to remember (except maybe for the brilliantly named “Boops boops“). “Thaumoctopus mimicus” tells you that this particular species is good at mimicry, even for octopus standards.

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Mimic octopus (Thaumoctopus mimicus) foraging on the sand

Both species live on soft sediment (mostly sand) habitats and they have evolved to be perfectly adapted to this lifestyle. They live in holes in the sand, are small, have longer arms than your average octopus, and their colours are quite drab. There are a few subtle physical and behavioural differences between the two though.

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Wunderpus partially in its hidey-hole

One of the things I noticed is that their hunting strategies vary slightly. Wunderpus have more extensive “webbing” between their arms than mimics and they use this webbing when hunting. Crabs are a favourite prey of wunderpus and they catch them by spreading their mantle (the “web” between their arms) over rocks, holes, or other objects like a big parachute. They then use the tips of their arms to poke the crabs out of their holes, after which they run into the parachute-web and are easily collected with one of the other arms.

Mimic octopus seem to forage more actively and (in my experience) use the parachute-technique less often. Instead they poke their long arms into holes in the sand, scaring out any critter that’s in there and then grabbing it directly. This means that mimics spend even more time moving over the sand than wunderpus do, which might be why they evolved some very particular behaviour.

Mimic

Trying to mimic?

Whenever you search for information about the mimic octopus, one of the first things to come up is that they mimic all kinds of other animals. Unlike other octopuses, it does not just mimic colour, but also the behaviour of up to 6 (or 8 or 12 depending on who you ask). The question is, does a mimic really mimic? Their mimicry is supposed to deter or fool predators or prey, but I wonder if this is really the case, or whether we are over-interpreting things from our human perspective.

Many of the behaviours that have been called mimicry could also be explained by simple logic or physics. Take for instance the idea that they mimic toxic flounders/soles while swimming. Yes, they do look very similar when they swim, but it is also a fast and energy-efficient way to swim over any flat area. Which is undoubtedly why this type of swimming is used by most octopus species living in the sand. Another example is the lionfish-mimic, which could also be explained as a way to look as big as possible when threatened. It’s a very common tactic used throughout the animal kingdom, and if you happen to be an octopus with long arms, you’ll look like a spiky lionfish when spreading them out. Other behaviours can similarly be explained, but I wouldn’t want to bore you with long lists right now.

Does this mean they do not mimic or that I am just a mopey cynical bastard who refuses to be amazed by a fantastic animal? Of course not! I love mimics and they show some  of the most extraordinary behaviour in the ocean. It just means that I want to learn more about them to find out what causes it.

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Close up of a mimic octopus

To study them properly, you first need to be able to tell the wunderpus and mimic octopus apart though! These critters look very similar (stripey), so it’s easy to get confused. Here is what to look for:

  • Arm patterns I: The black/white patterns on the arms of Wunderpus are very sharply defined, compared to more blurry with the mimic. Imagine the patterns on the wunderpus were drawn by a German painter using a pen and ruler, and the ones of the mimic by me with some crayons.
  • Arm patterns II: Mimic octopus have a continuous white outline along the border of each arm. The wunderpus does not have this, instead the band-pattern continues across the border.
  • Head: Mimics have a “U-“-shape on the back of their head, where wunderpus have a white patch.
  • Colour: Wunderpus usually have more of a red/brown colour shade to them than mimics, which are almost always black and white. Careful though, they can both change colour so this is not the best way of telling them apart.
  • Behaviour: The hunting behaviour I described earlier is a hint, though not always consistent. From my experience, wunderpus live in areas where the sand is more coarse (gravelly) than mimic octopus, which could also explain why they have slightly different hunting methods.

Finally, because you made it this far, here is a video I took of mating mimic octopus in Indonesia:

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Ocean pretenders: Eat or be eaten

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Algae or  a pipefish pretending to be algae?

At some point or other, all of us have pretended to be something that we are not. From trying to look old enough to buy alcohol as a teenager, to keeping your head low and pretending to be a pot plant in the corner of the office when the boss is looking for someone to take notes during a meeting. Some people might pretend more often than others, people might have good reasons for wanting to look like someone (or something) they are not, and some individuals might have less than innocent intentions when hiding their true identity. The same thing happens in the oceans but the stakes are usually higher than (trying to) look cool with a beer, or the tedium of having to take notes. A critter’s skill at pretending often means the difference between getting dinner or being dinner…

The ocean-pretending I am talking about is more commonly known as camouflage and mimicry. The terms are frequently mixed up or even assumed to be synonyms, but they are two different concepts. To distinguish between the two, it helps to know that the goals of camouflage and mimicry are opposite from each other. Animals using camouflage are trying very hard not to be seen, like you trying to be a pot plant instead of a potential scribe. Mimicry attempts to do the opposite: wanting to be seen, while hoping observers will believe you are someone else, like our teenager bluffing he’s old enough to drink.

Usually when biologists (who know their shit) talk about camouflage, they are thinking of mobile animals that are pretending to be objects or animals that don’t move; these objects could be plants, rocks, sand, sponges, etc. When those same biologists talk about mimicry, they mean active animals that pretend to be different species of active animals. But that is just the start of it, the obvious question is why? What are the reasons behind camouflage and mimicry? As a rule, fish don’t like alcohol, so there must be some other cunning plan.

For camouflage it boils down to two options: defensive or aggressive. People tend to intuitively understand defensive camouflage: hiding so you don’t get eaten or killed. Two ocean examples are seahorses pretending to be seafans or crustaceans looking like sponges. Aggressive camouflage is when an animal tries not to be seen, so it can eat unsuspecting animals coming closer. Frogfish are masters at this, so are most scorpionfish, and many other species. It is perfectly possible for an animal to use both defensive and aggressive camouflage at the same time. Think about the human version: soldiers wearing camouflage do not want to get shot, while aiming their guns at the enemy.

Mimicry has similar uses, depending on what the animal mimics. Unlike camouflage, mimicry needs a distinctive “model species”, which is imitated by the “mimic”. Depending on the nature of the model and the mimic, we distinguish three kinds of mimicry. Batesian mimicry has a dangerous model, but a harmless mimic. Mullerian mimicry has a dangerous model and a dangerous mimic. The last type, Peckhamian mimicry, has a harmless model, but a dangerous mimic.

Batesian mimicry can be compared with our teenager trying to buy alcohol. He might try to look like the real deal, but really is not. A great ocean example is the (non-toxic) baby pinnate batfish (Platax pinnatus), which look like a toxic flatworm. Or baby sea cucumbers pretending to be toxic nudibranchs. Predators assume the mimic is toxic, so they avoid eating it, good news for the mimic!

In Mullerian mimicry both mimic and model are “the real deal”.  This is very common in nudibranchs of the Phyllidiidae family. Most species in this family are very toxic and they all look very much alike. When a predator tries to eat one species, he’ll learn to avoid the other similar looking species as well. A bit like the leather-clad members of different motorbike gangs which look equally dangerous to outsiders. The bikers can tell the difference between other gangs, but I would advise against picking a fight with any of them.

Peckhamian or aggressive mimicry happens when the mimic pretends to be a harmless model, usually to get close to prey. This method is used by predators like dottybacks, who pretend to be harmless damselfish so they can get close enough to juvenile damselfish to eat them. A (purely hypothetical) human example could be a person living in a fancy white house, who pretends to be a silly orange clown, but in reality is a dangerous would-be dictator. As it turns out, land is no different than the ocean: the animals that believe in the illusion are most likely to suffer from it.

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Aggressive camouflage in action: this dragonet failed to see the lizardfish hiding in the sand.

Flamboyant Cuttlefish

It’s been a long time since I put a critter in the spotlights, so it’s time for one of my personal favourites: the Flamboyant Cuttlefish! I am definitely not the only one to like this amazing little animal, for most divers it is high in the top 10 of critters to see. With good reason as well, Flamboyant Cuttlefish are one of the most beautiful and intriguing inhabitants of sandy dive sites.

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Flamboyant Cuttlefish (Metasepia pfefferi) striking a pose

The small cephalopod many divers call “Flamboyant Cuttlefish” are in fact two species: the Flamboyant Cuttlefish (Metasepia pfefferi) and the Paintpot Cuttlefish (Metasepia tullbergi). The first one lives in Malaysia, Indonesia, Papua New Guinea and the north of Australia. The Paintpot Cuttlefish is found further north, from the Gulf of Thailand all the way up to southern Japan. Both species are classic muck dive critters, they only occur on muddy or sandy bottoms, so you will have to move away from coral reef to encounter them.

flamboyant-cuttlefish3So why does this animal deserve the effort of searching sandy plains for days on end, in the hope catching a glimpse of it? To start with (the name is a bit of a give-away) they are very flamboyant critters. We are talking yellows, pinks, blacks and whites, all at once! If that wasn’t enough, they often change their colours into “traveling waves”, even more so than normal cuttlefish or octopuses. From my experience, smaller Flamboyant Cuttlefishes have the brightest colours and make the most extravagant displays. When I write small, I do mean really small: adults do not grow much bigger than 8cm. They ideally sized Flamboyant Cuttlefish for the best colour-show  would be around 3-5 cm!

If finding an animal that size seems difficult, you might also want to consider the following. When they are not disturbed, hunting, or mating, Flamboyant Cuttlefish are anything but flamboyant. In their “standard” state, they blend in perfectly with their background, so they will be a mottled grey, brown, or black. For this reason some divers or photographers are tempted to disturb the animal to better see its colours. It is obvious that this is a bad idea, as it will stress out the cuttlefish. Be patient  instead, observe it for a while and you might even be rewarded by seeing it hunt small shrimp, lay eggs, or even mate!

Another thing that is special about them is that they do not swim, but walk across the bottom. To do so they use two of their arms and an adaptation of their mantle. They can swim, but only do so when they’re startled and over short distances. I could easily spend an entire dive watching these guys wander across the seafloor, little blobs of colour on a quest to eat as many shrimp as possible. It might be because of the awkward way they walk, but I always imagine them to be mildly grumpy animals. A bit like an old man with stiff joints who can’t walk that well, grumbling to himself about how the terrible weather…

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A juvenile Flamboyant cuttlefish (M. pfefferi) walking across the rubble

An interesting mystery surrounding these animals is whether or not they are toxic. Their colours would suggest some form of aposematic colouration, in the same way nudibranchs advertise their toxicity with bright colours. Some authors have even suggested flamboyant cuttlefish might mimic nudibranchs such as the Ocellate Phyllidia (Phyllidia ocellata). I have however, not read a single bit of conclusive evidence of this. It seems to be one of these “facts” people have assumed, written about and then it just got copied. To date there seem to be no papers out their describing whether or not Flamboyant Cuttlefish really are toxic, and which toxin they would produce. If anyone would have come across that information, I would be very grateful if you could share it with me and the rest of the world.

As is often the case with small critters, we don’t know very much about them. But that doesn’t have to stop us enjoying looking at them. Which is why I couldn’t resist adding a video of one of these guys. The title is a bit too sensational, but the footage is great, enjoy!

 

 

Holiday special – Feeding time!

Now the main holiday madness is over, we are all starting to take stock of the damage done by the excessive eating and drinking we’ve been doing. Or at least I am doing so… In this time of year, we can all relate to the feeling of being way too full after that unnecessary third helping of dessert. Compared to other animals we’ve got it easy, all we have to do is cook or order our food and start stuffing ourselves. It’s slightly different with the critters we find in the ocean.

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Lizardfish eating a dragonet

While there is a lot of active hunting happening in the ocean, many of the species I study are ambush predators. This means they are even lazier than we are when it comes to getting food. They spend nearly all of their time lying down on the ocean floor, waiting for dinner to swim by and then gulp it down. The plus side of this is they can’t get annoyed with themselves for not ordering the more delicious looking plate their neighbour is wolfing down. The downside is that they sometimes have to wait a long time until dinner swims by.

When you are an ambush predator, being camouflaged is particularly important. If you look like what you really are (a hungry fish), no tasty morsels will be tempted to swim anywhere near your mouth. Camouflage that helps animals hunt is called “aggressive camouflage” and sometimes “aggressive mimicry”. The difference between the two is that camouflage refers to animals pretending to be a plant or dead object like a stone. Mimicry refers to pretending that you (or a part of you) are a harmless or tasty living animal such as a herbivorous fish, worm, …

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Aggressive camouflage: Estuarine Stonefish (Synanceia horrida) looking like a rock covered in algae and sponges

Good examples of critters using aggressive camouflage are stonefishes and lizardfishes. They pretend to be rocks or blend in with the sand, waiting for a bite sized morsel to swim by. Aggressive mimicry is used by many species, but it is perfected by frogfishes. They use a modified fin ray as a fishing rod, the bait on top of it (or “esca” if you want to sound all sciencey) has evolved to resemble a small animal like a shrimp or worm. This bait is wiggled around until an unsuspecting fish gets too curious for its own good and ends up as prey. In one species, Antennarius hispidus the esca (=bait) has even been found to contain bioluminescent bacteria, great for luring in snacks at night. Frogfishes are not the only fish using a bait to attract meals, this technique is also used by some flounders and stargazers.

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The inside of the mouth of a giant frogfish (A. commersoni)

If you have ever had a fish tank and tried to catch your fish bare handed while cleaning it, you will know that no matter how nearby a fish is, it’s hard to catch one. So ambush predators have a number of adaptations to make this easier. Most of them have a huge mouth that sucks in a lot of water when they open it quickly. This suction feeding causes the fish to get sucked into the predators mouth together with the water. On top of that, the teeth of most of these predators are pointed inward, making it easier to hold slippery prey. Another funky adaptation are “pharyngeal teeth”, small teeth on the inside of the throat that hold the prey when the predator opens its mouth to get a better grip on it. You’ve read that correctly, as if frogfish weren’t weird enough already, they also have teeth in their throat.

While most of us only binge eat on special occasions and then feel guilty about it, frogfishes and other similar predators really don’t care. They eat whenever they can, as much as they can. When you think you’re exaggerating, remember this: the mouth of a frogfish can expand to 12 times its normal size when eating. The equivalent of this would be you fitting an entire chicken in your mouth when eating. Frogfishes can also eat prey that are up to 1,5 times bigger than themselves! For us, this would be roughly the equivalent of eating a whole pig for Christmas, which would make for some interesting scenes around the dinner table…

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A Scarlet Frogfish with prey in its stomach (source)

So next time you’re feeling stuffed at holiday eating fests dinners, remember it could be worse 😉