Yes, a clickbait title again. Soon I’ll have fallen so low as to make lists like “Five facts you didn’t know about the wallaby.”
Anyway, I’m glad to see that today’s New York Times Science section has some real science beyond human health. Click on the screenshot below to go to a short article and cool video about the highest acceleration and relative power output by any vertebrate. It’s in a chameleon:
The short piece highlights the work of Christopher V. Anderson, a postdoctoral researcher at Brown University. His website includes a link to his thirteen videos on chameleon feeding behavior, and I’ll put one of them below. Here’s a bit from today’s NYT piece (my emphasis)
The smallest chameleon [Anderson] tested, Rhampholeon spinosus, not only had this long tongue extension, but, as he writes in a paper published in Scientific Reports, it also demonstrated the highest acceleration and power output for any movement by a reptile, bird or mammal. Small insects and mantis shrimp put larger animals to shame.
The acceleration was about 8,500 feet per second per second, which meant that the tongue was pulling about 264 gs. And the power output was 14,040 watts per kilogram (about 2.2 pounds).
Anderson hypothesizes that the greater relative tongue extension of smaller chameleons rests on their requirement for relativly more food based on a higher metabolism. You can read his paper in Scientific Reports for free (reference and link below). Here’s my summary:
Anderson measured the tongue projection length, speed, acceleration, and power in 55 individuals (279 events) in 20 species of chameleons in nine genera. Here are the graphs of those statistics plotted against snout-vent length (“SVL”) in each species. Plot A shows projection distance, B peak projection velocity, C peak projection acceleration, and D peak projection power relative to body mass. As Anderson predicted, the power of the shot (but not the velocity) is higher in smaller species, and while bigger species can extend their tongues bigger distances, smaller species can extend their tongues relatively longer distances, i.e., smaller species can catch prey at greater distances relative to their body size—proportionately greater distances. (The relatively greater projection distance in graph A is shown by the slope of the black line being significantly smaller than that expected from body size alone—the slope of “expected” light gray line assuming tongue projection scales exactly to body size. Because smaller chameleons fall above the expected line, they extend their tongues farther than expected under 1:1 scaling.
Compared to other species, these data show that chameleons show the highest peak accelerations and mass-specific power of any known amniote (mammals, reptiles and birds). Here are some data adduced by Anderson:
Look at that rate of mantis shrimp striking acceleration: 104,000 meters/second/second! That’s 232,641 miles/hour/second (i.e., if that acceleration were maintained for one second,the claw would be traveling at over 232,000 miles per hour.
The big question: why do smaller species show greater power and relatively greater tongue extension. Anderson assumes the relationship is adaptive (note: it may not be!), and says it’s connected with the relatively higher metabolic needs of smaller species. He gives another hypothesis, which I won’t describe, but his data support the metabolic theory. As the paper notes:
Given the higher mass-specific metabolic rates of smaller animals, small chameleon species may be under pressure to increase the effectiveness of their feeding apparatus in order to mitigate metabolic scaling constraints. Under this scenario, one would expect small chameleons to project their tongues proportionately further than large species and be capable of capturing larger prey.
This study found. . .that both peak acceleration and power output scaled in direct proportion to body size, suggesting that the energy potentially lost due to high accelerations is not reduced in small species by having proportionately lower accelerations for their body size. On the other hand, with proportionately longer jaws, a proportionately larger tongue apparatus, proportionately larger tongue muscle cross sectional areas, and a proportionately longer tongue projection distance relative to their body length, small chameleons have effectively increased the relative size of their entire feeding apparatus. In doing so, small chameleons have increased the functional range of their prey capture mechanism, and are likely able to capture and process larger prey items than they would otherwise be able to if their muscle cross sections and jaws were not disproportionately large for their body size. is inference is supported by the selection of proportionately larger prey items by the smaller of two morphological forms in Bradypodion. These patterns are thus consistent with those that would be predicted for mitigating metabolic scaling constraints, which may be involved in driving the observed morphological scaling patterns.
I’m not sure, though, whether smaller species of chameleons really do have a higher mass-specific metabolism than do larger species. The author cites five papers in support of that hypothesis, but one is on mammals,one on birds, and one on amphibians. We know that in mammals and birds the mass-specific metabolism is indeed higher in smaller species (they lose more energy in radiated heat since their surface area-to-body mass ratio is higher). But I haven’t read the other two papers on reptiles (one is on the desert chameleon alone, so it’s not relevant), so I’m not sure we have the information for reptiles showing higher relative metabolism in smaller species. After all, reptiles are, in contrast to birds and mammals, ectothermic (they regulate body temperature externally from the environment, rather than keeping a constant temperature from metabolic heat). That might eliminate the surface area/body mass relationship that obtains in birds and mammals, who have to balance heat loss through the body against heat production in the tissues.
Here’s one of Anderson’s videos showing the famous Jackson’s Chameleon (Triceros jacksonii, a native of Africa) snagging a grub. After clicking on the arrow, then click on the underlined words on the screen to go to the video on YouTube.
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Anderson, C. V. 2016. Off like a shot: scaling of ballistic tongue projection reveals extremely high performance in small chameleons. Scientific Reports 6:18625.
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Wouldn’t it simply be that matter (chemical bonds) is relatively stronger on smaller scales, and that the bigger you make something the harder it is to make it strong enough?
Trying to control for variable between species is difficult, but as a general rule smaller muscles are stronger muscles, gram for gram. A muscles’ strength is proportional to its cross sectional surface area, which increases in bigger muscles by a square function, but a muscle must also overcome its own weight to contract (and move a load), and weight increases by a cubed function.
So bigger animals will have proportionally bigger muscles with bigger x.s. surface area, but they have disproportionally greater weight to move as well. It seems to work out, then, that smaller muscles come across as stronger, gram for gram. Its kind of like they operate in a lower gravity environment. So that seems to mean they can get moving faster, hence a greater acceleration.
Another factor to consider, which I think is important for chameleon tongues, is acceleration not directly due to muscle contraction but due to hydraulic effects. The tongue extends b/c of contraction by circular muscles — that is by muscle fibers that wrap around the inside of the circumference of the tongue. When these contract, that displaces the soft tongue forward by a hydraulic action. Anyway, a smaller tongue might be able to squooosh the tongue forward faster. I have not worked out why that might be.
It’s hard to make big things move. Everything naturally vibrates with a power law spectrum, peaking at low frequencies. The larger the objects the the lower the frequency.
At Brownian motion scales the frequency increases as particle size decreases. The motions get faster, but the length of the motion is shorter. On ballistic scales, accelerations can be quite high (>10^4 g) for small particles.
On the power side, its a function of storing and utilizing chemical energy quickly. Shrimp and chameleons have found niche uses for their quick movements, but they cannot do them all the time.
I’d be very interested in reading about 5 things I didn’t know about the wallaby. I don’t know much about them at all, tbh, so anything would be an improvement! They used to live in the wild in the Peak District in the UK (they escaped from somewhere, obvs), but eventually went extinct in the early noughties. My late colleague, Derek Yalden, studied them. – MC
There are still rumoured sightings of the things.
Sign me up! Wallaby facts!
I hadn’t studied it, but I thought they had been deliberately caught and either re-homed or fed to the Endangered Species Club or something.
I may be thinking of coypu who disappeared from the Fens or Broads about the same time ; they’d have been more obviously economically damaging( eroding waterway banks, especially in the Broads) and they’d have been in competition for living space with species whose re-invasion of the waterways was desired (otters and water voles spring to mind).
Hmmm, photos of Peak Wallabies from 2009. That’s recent enough to not consider them extinct just on the basis of “haven’t been seen for a while”.
Wallabies visit my back yard most days. I’m sure that I can come up with five facts about them.
If the mini-me version of the chameleon was exactly to scale, the critter would have to get closer to the prey, which risks scaring it off. Greater speed and reach may just compensate for that.
I am trying to work out why invertebrates can have greater acceleration. A big factor seems to be that they organize the innervation of muscles differently from vertebrates. The commonly known way in which muscles are innervated is really how vertebrates innervate muscles. Here, a motor neuron innervates a muscle cell at only one point. Thus when the neuron delivers an action potential to a muscle cell, that a.p. is delivered at only one point, and this means it takes time for the a.p. to propagate over the muscle cell surface and penetrate into the cell to initiate contraction. Contraction therefore is a bit gradual, limited by how fast the a.p. can get to the different contractile units in the long muscle cell (and muscle cells can be very long). A muscle in a vertebrate will have a lot of muscle cells, and how fast the muscle can contract is effected by how quickly muscle cells are recruited (action potentials arrive at different times), and the muscle contracting to a degree to overcome the weight of the muscle and whatever load it is carrying.
In insects, otoh, a motor neuron innervates a muscle cell at MANY points along the length of the muscle cell, and this means that a delivered a.p. results in a simultaneous and therefore faster contraction of the muscle cell along its entire length. Also, insect muscles have far fewer muscle cells, and so recruitment of cells sufficient to get a muscle to contract is also a lot faster.
This is all explained in this educational video: http://www.physioviva.com/movies/insect_muscle_innervation/index.html
That would work if the propagation speed of action potentials in muscle was a lot slower than the speed in nerves. Which I’m not equipped to answer myself, but it is a point needing checked.
I believe that for arthropods, which includes the aforementioned mantis shrimp and insects, they also use one simple trick (see what I did there?) of having an exoskeleton, which permits more advantageous attachment points of muscle origins and insertions, resulting in better leverage and generation of force during contraction, relative to vertebrates. Greater force, greater acceleration.
This is a very interesting talk by a biologist who studies mantis shrimp.
Shorter version is it seems that the shrimp can store energy in flexible areas of the exoskeleton.
The video is well worth watching!
I sense an Ig nobel price waiting for Mr. Anderson …
Not necessarily, unless you accept Anderson’s metabolic theory and awaits his result on the minuscule, protected chameleon the NYT article describes. His reference to plethodontid salamanders [lungless, cool!] have higher values on both peak acceleration (458 vs 264 g) and power densities (18 vs 14 kW/kg), and its directly comparable tongue projection too.
NYT looks at the latter, apparently: “a paper published in Scientific Reports … also demonstrated the highest acceleration and power output for any movement by a reptile, bird or mammal”.
Now I wonder if not those salamanders, ectothermic and oxygen limited in a sense, are a problem for the metabolic theory? So maybe the amphibian paper may be the key.
“its” = it is.
I sense a great opportunity for a “Godzilla vs chameleon” flick.
The speeds are in fact beyond astounding, not just for chameleons but for all the other examples. Astounding, at least, to someone who thought pronghorn antelope were fast.
I wonder whether the energy metabolism of the high-speed organs is different.
Yes, but those are one-shot movements. Whereas antelope speed is continuous motion of the entire antelope. Not really comparable.
cr
Excellent article!
I’m curious about the claim that smaller chameleons [or lizards in general] have significantly higher metabolic demands [per gm] than larger ones. This is obviously correct for homeotherms e.g., birds and mammals, but does metabolism generally scale with body size for a group of poikilotherms with common body plan and life-style [for chameleons, slow-stalking or ambush predators]?
Just realized, it’s 2016! The 100th anniversary of the arrival in Hawaii of the Brush-Tailed Rock Wallaby! A pair escaped from a private zoo, as a pack of dogs killed the joey. A little googling will yield more info and photos. May be 40 or so. They are found in a side gulch of Kalihi Valley. Used to climb up there with my students to check them out, 45 years ago.
Supposedly another escapee was a bear, with a collar around its neck. Hunters would report sightings for many years after, or so the story goes.
OK. Posting here to show I read it, it was interesting, and I’m glad you post things like this. I don’t have anything useful to add, though.
In the animal world, power comes in small sizes. I recall how they use to compare the strength of ants to humans and it was no contest. To a chameleon we are nothing.
And we didn’t even mention the pistol shrimp!
I wonder if on an even smaller scale than mantis shrimp clubs and flea legs, on unicellular and even prokaryote scales, we might not find even faster accelerations.
Does anyone have any reliable information the acceleration of a human punch, or kick (this would be an interesting point of comparison)? The best I could find in a brief internet search was the force behind punches from professional boxers (which at 1000+ psi is rather terrifying). But, I couldn’t find anything specifically on maximum acceleration. My guess would be that a kick would be the likely candidate for fastest acceleration in the human body.
And the prize for the most uninformative unit conversion goes to – the New York Times.
“And the power output was 14,040 watts per kilogram (about 2.2 pounds).”
Okay, so a kg is 2.2 lbs. Most of us knew that. Not really a very illuminating figure in any case. Per kilogram of what? Tongue? Chameleon body weight? The NYT doesn’t say.
Though from Anderson’s paper it seems to be per kilogram of body weight. I think all those mentions of power in the discussion should be suffixed ‘per body weight’. Which seems to be a distinction a bit beyond the NYT.
I’m not sure whether these measurements of instantaneous power output of a one-shot mechanism are really meaningful, except for comparisons in a carefully defined context.
Disclaimer: I’m an engineer, not a biologist.
cr
I was so happy to see that in the NYT yesterday! Fascinating stuff.
I used to keep Rhampholeon brevicaudatus and spent hours attempting to get photos of their extended tongues. Once in a while I succeeded. The timing was difficult given the instantaneous tongue action and the focusing lag of digicams. (Yes, you had to keep the shutter half depressed to hold the focus while waiting for the cham to go off; which usually took forever, since everything else about chams is slow as molasses…)