Fishes mimic leaves

September 26, 2014 • 12:52 pm
 

In about three weeks I’ll be giving a popular lecture on evolution in Bulgaria—that’s right, Bulgaria! I’m very excited, for who ever gets to go to that country? I will, and will spend a week travelling about, seeing the sights, consuming the local comestibles (including the famous yogurt), and, of course, meeting the local biologists.

They wanted a talk that would interest a general audience (it’s part of a public lecture series) but also teach them some evolution. Since I’m tired of the evidence-for-evolution talk, I decided to talk about mimicry. You know from my (and Matthew’s) many posts on the topic that I have a keen interest in it, as mimicry is not only one of the nicest examples of evolution by natural selection (no, Larry Moran, it can’t be due to genetic drift!), but one that shows how far natural selection can take an animal (or plant), despite various developmental and ecological constraints, to its “optimum”: looking like something else that you know. How close can it get? We know from the leafhoppers and frogmouths we’ve seen that it can get pretty damn close, not to mention Matthew’s blasted nightjars. There are other lessons about evolution to be learned from mimicry, too: things about frequency-dependent selection (polymorphic Batesian mimicry, failure to adapt (the hosts of cuckoos), and so on.

Mimicry is also a good topic for a show-and-tell talk, because there are so many stunning cases of it, which will wow an audience if they have the least interest in biology (just keep reading this site and you’ll see lots more).

And selection can take a species pretty damn close to where it “should” be. Case in point: the leaf fish Monocirrhus polyacanthus from Amazonia, an example I came across while preparing my talk. The fish has evolved both its appearance and behavior to mimic a floating leaf, all to get its prey. They are voracious hunters, and lightning fast in their nomming.

A description from Ichthyologist Tumbler:

An incredibly-adapted species, this fish is camouflaged to mimic a dead leaf, both in body shape and pattern. It can change colour to match its surroundings and has a projection from its bottom lip that resembles a leaf stalk. When hunting, it stalks its prey in a head-down stance, appearing to drift towards it like a dead leaf drifting in a current. When it strikes at an item of prey the entire mouth protrudes outwards, forming a large tube into which the prey is sucked, usually head first. This happens so quickly it is often difficult to see. It can swallow prey almost as big as itself in this way.

A video of their behavior in an aquarium, which is anything but fishlike:

Here’s a video (with very annoying music) showing them hunting and eating:

And a photo of some specimens. The photos on the web show a variety of colors for this species. Notice that not only the mouth but the tail has evolved a point, so that the whole thing looks like a leaf:

tumblr_m336mfmPRo1rprj1yo1_500

I bet you didn’t know that there were leaf-mimicking fish.

30 thoughts on “Fishes mimic leaves”

  1. I was wondering how they controlled their posture without visibly moving their fins. At about 2:25 in the 1st video you can see they have a pair of transparent fins just behind their gill covers, busily working away to maintain the ruse of a nonchalantly drifting leaf.

    1. Good observation! I didn’t catch the transparent fins until I re-watched and scrutinized the fish at 2:25.

  2. Interesting. How did this get set up?

    Bulgaria is an interesting case in that while it was an officially atheist country in the past, religion was never really attacked properly (by developing critical rational thinking in schools) and as a result atheism these days is only mentioned in the public sphere in connection with the evils of communism and as a position no “normal” (especially in the political sense) person would hold. In that it’s actually worse than the situation in the US, because while in the US many people are deeply religious and in Bulgaria they’re not, when atheism is mentioned, even on FOX News and the likes, it is at least presented, while in Bulgaria it’s as if it does not exist. And a whole generation has now grown up in that kind of media environment.

    Also, evolution is taught in school and is no danger of being banned like they tried to do in Serbia, but it is not taught very well, and it is almost absent from the university curriculum in biology and completely absent from what everyone else studies (in Bulgaria there is no such thing as a common core in universities. students specialize from the very beginning). The result is that the majority of people are very much ignorant of the subject.

    I’ll be curious to see what your impressions are.

        2. I didn’t know they could resemble seaweed (not counting horsefish) until I saw something very similar to this guy on a lazy snorkeling afternoon on the big island of Hawaii.

          After having just swam with a very friendly turtle in the shallows, I was headed back to shore, very slowly – just drifting in about 3 feet of water, watching the seaweed bits blowing back and forth in the surge. One little bit of seaweed seemed to be doing the impossible in the current — while all the flotsam was blowing back and forth with the surge, one little tumbling piece always made it to the extremes, blowing impossibly widely back and forth – to the leading edge of the flotsam, both directions. Something wasn’t right, so I froze and observed.

          Eventually, I was able to make out the fish body and its little psychedelic eyeballs. It had curled its body into the shape of an S, and was tumbling over its seaweed-shaped fins, rolling like a ball, but obviously adding a little umph of its own, which is why the tumbling was a little more than expected under the circumstances.

          A year or so later, I told the divemaster who certified me about it (and also the frogfish (the one on the left) I saw in the Caymans), and he nearly threw a fit. He said he probably had more than 5,000 dives under his belt, and has been unable to see either of those critters.

          1. You make me nostalgic for Big Island. I sat at the shore next to a nice turtle when I was there and the water was so clear that there was a little area where you could see eels and other pretty fish.

          2. funny that I said “horsefish” instead of “sea horses”… but I’m glad that made sense.

            Here’s where it happened. On my way back in, as I’m regrouping with the folks I was with, I notice a couple tourists pointing and screaming “SHARK”, pointing out at that little cove.

            I looked out into the cove, and despite having just swam with turtles and psychedelic fish, my heart sank a little. If I had stayed out a few minutes longer, I could’ve swam with a couple porpoises, too. They were swimming around in 4-feet of water. (which made their distinctly-shaped fins stick out of the water wherever they went).

      1. The last time this happened, not only did I not remember, but I replied with the exact same comment!

  4. “I bet you didn’t know that there were leaf-mimicking fish.”

    Oh yes I did! I worked in a tropical fish store for two summers while in high school in the 1960’s. But the thing I remember even more than leaf fish was the great sign that hung in the store window: “Children under 12 prohibited (unless accompanied by money).”

    1. I remember being in Seattle years ago and seeing a sign hanging in a pet store window that was located next door to a Starbucks: Unattended children will be given two shots of espresso and a free puppy.

    2. Yep, I always wanted to have some leaf fish back when I was wild about tropical fish. Never had enough tanks, though.

      1. I’m not fancy enough for such fish. Gouramis are about as complex as I go though I used to have hatchet fish. I stopped getting them because it’s not the right environment for them and I think they catch them from the wild instead of breeding them.

          1. I’ve had many a betta that built bubble nests. I knew they were healthy when they did so.

            I have two pearl gouramis right now & I’d like to get some dwarf gouramis but keep forgetting to go to the fish store!

  5. Fascinating…I have never seen these drifting leaf mimicking fish. I liked it when the video panned to the bottom and the fish down there slowly floated up for a few seconds. Reminds me of how sea-dragons mimic seaweed with the same innocuous drifting. “Nothing to see here…continue on,” and then gulp!

  9. Check out the tripletail, Lobotes surinamensis. Not only are the juveniles leaf like in appearance and behavior, but adults float on their side on the surface and pass for a bit of flotsam. I think there are a couple of other leaf mimicking species, but I will have to let my memory work a while.

  10. There is a second South American leaf fish, Polycentrus schomburgkii. Also check the African leaf fishes of the genera Afronandes and Polycentropsis.

    1. There is an African cichlid that mimics a dead fish. It lies on its side, looking, well, dead. When a little fish comes close for a nibble…

  12. Are religions a form of mimicry ? Maybe religion mimics reality ? The stories of religion recorded in scriptures succeed because though wildly improbable they appear to still be ‘possible’ and contain ideas that people wish to be real.
    The shaman / priest uses their stories to trap and parasitize their flock. If people had sufficient knowledge of history & science and tried to apply them critically to the religious stories then they would soon see the difference between the mimic of reality and probable reality.

    Are the errors of scripture like Cordyceps fungi ?

    See. Cordyceps: attack of the killer fungi – Planet Earth Attenborough BBC wildlife on Youtube BBCWorldwide channel

    Maybe the opposite of religion is the theory of evolution as it gives the reality that everything evolves by very gradual processes where as religion expects instant mysterious magic. The religious stories can be seen to have evolved from Torah to O.T. to N.T. to Koran to Book of Mormon to Watch tower. Maybe the Koran virus has lost its eyesight like the Mexican tetra or blind cave fish (Astyanax mexicanus) The Koran has had the tolerant ideas found among the N.T. mix stripped out. It has lost the inner conflict of the debate- were we meant to follow O.T. laws or Pauls idea of living by spirit guidance? So instead of healthy doubt there is more unhealthy tendency towards certainty to follow barbaric 7th century morality.

Comments are closed.