An animal with gears!

Reader Stephen Barnard, occupier of Paradise in Idaho, called my attention to a new article in Science which, sadly, I don’t have time to read (I’m off to Cracow in an hour or so). But it reports that the nymphs of an “issus” (a genus of planthopper on the order Hemiptera, or “true bugs”) have gears on their legs: the first example of a cog-like mechanism in animals. I’ll give the abstract and then show a YouTube video that will tell you how the gears look and work.

Here’s the paper’s abstract:

Gears are found rarely in animals and have never been reported to intermesh and rotate functionally like mechanical gears. We now demonstrate functional gears in the ballistic jumping movements of the flightless planthopper insect Issus. The nymphs, but not adults, have a row of cuticular gear (cog) teeth around the curved medial surfaces of their two hindleg trochantera. The gear teeth on one trochanter engaged with and sequentially moved past those on the other trochanter during the preparatory cocking and the propulsive phases of jumping. Close registration between the gears ensured that both hindlegs moved at the same angular velocities to propel the body without yaw rotation. At the final molt to adulthood, this synchronization mechanism is jettisoned.

You can find the Science paper here (reference below, but article is behind a paywall). The video shows the entirely fortuitous way this phenomenon was discovered:

Here’s a figure from the paper, with its caption:

F1.large

Fig. 1 Gears on the hind trochantera of Issus nymphs.
(A) Nymph viewed from the side. (B) Gears on the left and right hind trochantera viewed posteriorly. (C) Scanning electron micrograph of the partially elevated articulation between hind trochantera and coxae and the engagement of gears on the two sides as viewed ventrally. (D) Higher magnification of the interdigitation of the gears. (E). Diagram showing the radius of curvature of the trochanter (ρgear), the angular placement of the teeth, and how the gears enmesh. (F) Profile of a gear tooth in Issus (left) compared with a man-made involute gear tooth (right). The radius of curvature of the fillet (ρfillet) is indicated.

SciTechDaily notes:

The finding demonstrates that gear mechanisms previously thought to be solely man-made have an evolutionary precedent. Scientists say this is the “first observation of mechanical gearing in a biological structure”.

. . . The gears in the Issus hind-leg bear remarkable engineering resemblance to those found on every bicycle and inside every car gear-box. Each gear tooth has a rounded corner at the point it connects to the gear strip; a feature identical to man-made gears such as bike gears – essentially a shock-absorbing mechanism to stop teeth from shearing off.

The gear teeth on the opposing hind-legs lock together like those in a car gear-box, ensuring almost complete synchronicity in leg movement – the legs always move within 30 ‘microseconds’ of each other, with one microsecond equal to a millionth of a second.

. . . This is critical for the powerful jumps that are this insect’s primary mode of transport, as even miniscule discrepancies in synchronization between the velocities of its legs at the point of propulsion would result in “yaw rotation” – causing the Issus to spin hopelessly out of control.

“This precise synchronization would be impossible to achieve through a nervous system, as neural impulses would take far too long for the extraordinarily tight coordination required,” said lead author Professor Malcolm Burrows, from Cambridge’s Department of Zoology.

. . . “These gears are not designed; they are evolved – representing high speed and precision machinery evolved for synchronization in the animal world.”

Interestingly, the mechanistic gears are only found in the insect’s juvenile – or ‘nymph’ – stages, and are lost in the final transition to adulthood. These transitions, called ‘molts’, are when animals cast off rigid skin at key points in their development in order to grow.

The question then becomes why the nymphs have gears but adults do not. The authors give a speculative answer:

It’s not yet known why the issus loses their hind-leg gears on reaching adulthood. The scientists point out that a problem with any gear system is that if one tooth on the gear breaks, the effectiveness of the whole mechanism is damaged. While gear-teeth breakage in nymphs could be repaired in the next molt, any damage in adulthood remains permanent.

___________

Burrows, M. and G. Sutton. 2013. Interactive gears synchronize propulsive leg movements in a jumping insect. Science 341: 1254-1256  DOI: 10.1126/science.1240284

37 Comments

  1. Posted September 14, 2013 at 9:05 am | Permalink

    Fascinating discovery! Great post.

  2. Alex Shuffell
    Posted September 14, 2013 at 9:08 am | Permalink

    This is a really exciting discovery. How long will it take for the ID-creationists to try to explain this with magic?

    • Posted September 14, 2013 at 9:10 am | Permalink

      The creationists have been doing that for two days already.

      • Mark Joseph
        Posted September 14, 2013 at 8:07 pm | Permalink

        Yes, but no matter how much they burble and babble, they are still doing nothing but poaching–after all, it was real scientists who discovered this mechanism, studied it, and wrote the article. All the creationists have done is to give the credit for it to their invisible magic sky ogre “intelligent designer” as well as sit back and say, “just like we predicted”.

  3. Posted September 14, 2013 at 9:38 am | Permalink

    Stunning! Each time a discovery like this comes up my jaw drops a little lower in awe at the sheer power of evolution!

  4. Gregory Kusnick
    Posted September 14, 2013 at 11:23 am | Permalink

    The question then becomes why the nymphs have gears but adults do not.

    Training wheels?

    • Torbjörn Larsson, OM
      Posted September 14, 2013 at 1:11 pm | Permalink

      =D

      Actually, the rest of hypothesis was (IIRC) that the adults were strong enough to cope without gears.

  5. Torbjörn Larsson, OM
    Posted September 14, 2013 at 1:07 pm | Permalink

    The Blind Gear-maker.

    • Torbjörn Larsson, OM
      Posted September 14, 2013 at 1:28 pm | Permalink

      The term reminded me of a what-if. (Come on, having gears would be awesome!)

      “Watchmakers” were the small hive-intelligent creatures genetically constructed to be construction crew for the Motes in “The Mote in God’s Eye”. These creatures didn’t have gears but (besides a 3d helper hand) a possible back solution – a pair of synovial joints.

      In the fictional universe they occasionally threw the joints, painful but not usually handicapping. And no other back problems until the joint wore out. Stiff upper lip though. 🙂

      WTF, Evolution!? Couldn’t you have gone in the direction of “less [parts] is more”?

  6. Posted September 14, 2013 at 1:12 pm | Permalink

    I’d love to know the evolutionary pathway for these gears, much the same way that Richard laid out the evolutionary pathway for the eye in that Christmas Lecture he did.

    b&

    • Torbjörn Larsson, OM
      Posted September 14, 2013 at 1:43 pm | Permalink

      What use is a half gear(wheel)?

      I would think even partial frictional synchronization of jump positioned trochanters would have been beneficial. And so on. [Handwaving frenetically.]

  7. Diane G.
    Posted September 14, 2013 at 1:14 pm | Permalink

    sub

  8. Posted September 14, 2013 at 2:43 pm | Permalink

    Reblogged this on Nerdy Life of Mine and commented:
    Vary cool

  9. Randy
    Posted September 14, 2013 at 5:17 pm | Permalink

    If gears evolved once, they can evolve many times.

    What I like about this is that, extrapolated a bit further, it makes the whole “what if you found a watch lying in the sand on the beach” argument for creationism less effective.

    While an actual watch would probably not evolve, gears are certainly an interesting first step. Who can say for sure? I wonder if centuries of selective breeding could produce an insect-watch.

  10. Marella
    Posted September 14, 2013 at 5:28 pm | Permalink

    Their explanation for the loss of the gears in the adult doesn’t make sense, unless a broken gear is worse than no gear at all, which seems unlikely, but is easily testable. They’ll just have to go and remove some of the teeth of those gears and see how the insect fares. It would also depend on how likely they are to break. Considering that evolution also had the option, presumably, to strengthen the teeth as well, if the loss of one or two was so catastrophic, I think they need another explanation.

    • Posted September 14, 2013 at 5:43 pm | Permalink

      Could it be that the strength of the material making up the teeth of the gears (chitin?) is simply not strong enough to withstand the force exerted by the adults’ larger muscles? It might be the case that *all* the teeth would simply get stripped after one, or a small number of jumps.

      Simply scaling up a design doesn’t mean that the larger version is viable.

    • Stephen Barnard
      Posted September 14, 2013 at 6:21 pm | Permalink

      I don’t know about issus, but in many insects the adult is a brief, transitory stage — gametes with wings and disfunctional mouth parts. Maybe they don’t need to jump.

    • Gregory Kusnick
      Posted September 14, 2013 at 7:04 pm | Permalink

      It’s clear that something doesn’t add up here. That fact that adults survive just fine without gears demonstrates that the gears aren’t essential and that breakage of them would not be crippling to the adult.

      And it seems to me the danger of breakage should be at its lowest in the adult stage. By then the hopper has learned to coordinate its jumps so that the stress on the gears should be minimal. And if the adult doesn’t need to jump at all, then not only are the gears unlikely to get broken, but it wouldn’t matter if they did.

      So this breakage story doesn’t convincingly explain why the hopper goes to the trouble of losing its gears in the last molt. There must be some other, positive advantage of not having the legs slaved together like that, such as better maneuverability, or the ability to vary the angle of the jump, or something along those lines.

      In other words, as the hopper’s jumping skill increases with practice, there comes a point when the gears change from an asset to a liability, and it’s time to take the training wheels off.

      • Posted September 14, 2013 at 7:14 pm | Permalink

        It’s possible that any potential stripping of the teeth in the adult might not be benign, and might carry with it some risk of structural damage harmful to the individual, such as weakening the substrate, in which case evolution would have no problem with selecting against them in the adult.

      • infiniteimprobabilit
        Posted September 15, 2013 at 1:37 am | Permalink

        Well, ‘real’ mechanical gear teeth are designed for so many (million) cycles of loading. Failure eventually occurs due either to fatigue cracking causing a tooth to break off, or the surfaces wear.
        I don’t know the relative life cycles of the larvae vs the adult, but it may be that gears can reliably function for the number of cycles a larva subjects them to, but not enough for an adult.

      • infiniteimprobabilit
        Posted September 15, 2013 at 2:17 am | Permalink

        Actually, I think there may be a far simpler explanation. If they’re anything like the leaf hoppers in my garden, the larvae don’t have wings and locomote by hopping, the adults have wings and fly – they still hop on takeoff, but I imagine their accurate-hopping ability is far less critical.

        • Gregory Kusnick
          Posted September 15, 2013 at 11:50 am | Permalink

          Perhaps so, but at best that tells us why adults don’t need gear teeth. It doesn’t tell us what harm they’d do if present.

          It presumably takes some extra developmental complexity to make the adult trochantera different from the juvenile ones. What selection pressure maintains that difference, if adult gear teeth are merely unnecessary?

      • darrelle
        Posted September 15, 2013 at 10:06 am | Permalink

        This is what really didn’t add up for me.

        “This precise synchronization would be impossible to achieve through a nervous system, as neural impulses would take far too long for the extraordinarily tight coordination required,” said lead author Professor Malcolm Burrows, from Cambridge’s Department of Zoology.

        It seems evolution must have solved this problem many times without the use of gears.

        Regarding nervous impulses, if the path length to whatever actuates the legs is the same to within a certain tolerance it doesn’t matter if the impulse speed is slower than the syncrhonization tolerance required for controlled jumps.

        Or, if there is only one of whatever actuates the legs, if a single actuator actuates both legs, then there is no nervous impulse synchronization problem. The only issue then is having the mechanical systems of the legs matching to close enough tolerance. Which is an issue in any case I can think of anyway, even with the gears.

        Whatever the case may be, it seems that evolution solved the problem for the adult form, so how on earth does that quote make any sense! It seems it is just plain wrong, or just not applicable. It must be me just not understanding something here.

        • Stephen Barnard
          Posted September 15, 2013 at 11:40 am | Permalink

          The adult stage of insects is often (even usually?) radically different from the larval stages. There are probably very different networks of genes controlling the development of larvae vs. adults. There is no reason to expect that gears should be present in the adult stage even if they might be adaptive.

          • darrelle
            Posted September 15, 2013 at 12:23 pm | Permalink

            Sure. I was thinking of insects, or even insect sized, organisms in general. This syncronization problem has been “solved” by evolution many times. I compared the example of the adult and larvae of this particular species because it seems to be a glaringly obvious example of the problem being solved without the use of gears.

            In particular nerve impulse conduction speed doesn’t seem to me like it would preclude achieving the necessary timing accuracy. Again, generally speaking, for any conceivable organism. We long since solved this same type of problem for electrical systems and I’d be surprised if evolution hasn’t come up with the same solution.

    • gravelinspector-Aidan
      Posted September 15, 2013 at 3:03 am | Permalink

      Imagine what would happen to an adult which “slipped” a gear (so that tooth L1 fitted between R2 and R3 instead of R1 and R2, where it should go). The insect would then yaw considerably on every jump so that it would land sideways or even backwards. Not good.
      That said, the solution presented down-thread sounds better : adults fly more often than they hop. Whether it’s actually correct requires additional info, but it certainly sounds plausible.

  11. Stephen Barnard
    Posted September 14, 2013 at 6:05 pm | Permalink

    The only thing the ID creationists have going for them is the argument from incredulity, which plays well to unimaginative people with fixed beliefs.

  12. Kevin
    Posted September 14, 2013 at 6:33 pm | Permalink

    Magical. So much that those little guys can tell us.

  13. infiniteimprobabilit
    Posted September 15, 2013 at 1:59 am | Permalink

    “The gears in the Issus hind-leg bear remarkable engineering resemblance to those found on every bicycle and inside every car gear-box. Each gear tooth has a rounded corner at the point it connects to the gear strip; a feature identical to man-made gears such as bike gears – essentially a shock-absorbing mechanism to stop teeth from shearing off.”

    That is really stretching things too far. First, bike ‘gears’ are actually chainwheels and bear little resemblance to involute gears, they’re designed to mesh with roller chains. Forget bikes.

    Second, the rounded corner at the base of an involute gear is deliberately there to avoid stress concentrations (not ‘absorb shocks’ as such), I would imagine the similar corner in the insects’ ‘gear teeth’ is a natural feature of the material it’s made from – insect tissue tends to have curved corners.

    And if one looks at the shape of the insect gears, they’re really very far from the ideal shape – for a gear tooth. But car gear teeth are fixed on rigid shafts which are held in alignment by bearings to within thousandths of an inch; I imagine the trochanters on the insect are far less accurately aligned – so the optimum shape for the insect gear teeth may well be quite different. In fact I’d guess that the long narrow shape of the insect gear teeth allows them to flex or ‘spring’ a bit to cope with the shock loadings caused by the fact that they don’t mesh precisely accurately – exactly the opposite of mechanical involute gear teeth, in fact.

    The fact that the insect has gear teeth is indeed remarkable; I just think the authors are getting carried away by their enthusiasm in trying to make too close a comparison to involute gears.

    Now, if they can find a natural gearset with helical teeth and synchromesh…

    • infiniteimprobabilit
      Posted September 15, 2013 at 2:06 am | Permalink

      Oh, and involute gear teeth are designed to function in a bath of extreme-pressure lubricant to avoid wear caused by the sliding contact at the engagement point. Without it, their life is short and noisy. What does the insect do about that?

  14. gravelinspector-Aidan
    Posted September 15, 2013 at 3:28 am | Permalink

    4th time of trying to reply to infiniteimprobability.
    bike gears : look inside a “hub gear” (“Sturmey-Archer” in EN_GB, don’t know about EN_US) ; also found in rod-operated brakes IIRC.
    Lubrication : fair point, but chitin microstructure and pores to lubricate the surfaces is within the normal insect structure gamut.
    Browser keeps crashing.

    • infiniteimprobabilit
      Posted September 15, 2013 at 6:10 am | Permalink

      I do know about Sturmey-Archer gears, but I have the impression that modern bikes almost always use multi-sprocket derailleur type gears instead. So ‘every’ bicycle (to quote the article) is much more likely to have chainwheels than true gears. But even if they have gears, my comment about involute machine gears vs. the bugs’ gears still stands.

      Re lubrication, I was asking a genuine question (i.e. not intended to be rhetorical). Obviously, the bug has found some solution to the problem. It may well be that chitin is self-lubricating, or that it just very slowly wears away (at a rate which is permissible within the design operating life).

      • darrelle
        Posted September 15, 2013 at 9:47 am | Permalink

        I don’t think these bug gears need lubrication anything like typical man made gear systems. They are not fully rotating gears spinning at sustained rpms. They move periodically back and forth over some fraction of a revolution.

        This bug gear system is much more similar to that on a winged or butterfly type corkscrew. Except instead of the gears each engaging an intervening “rack” they directly engage each other. But the basic function, to keep the two appendages movements, over some fraction of a revolution, synchronized.

        • infiniteimprobabilit
          Posted September 15, 2013 at 11:51 pm | Permalink

          Good point. I guess we’re unlikely to ever see true fully rotating gears in nature, not least because of the difficulty of making any sort of living-tissue connection to a rotating shaft to keep it nourished/replenished. (I know bacteria have done rotary motion, to the delight of the ID fraternity, but that’s on a microscopic scale, the conditions are different).

          • Gregory Kusnick
            Posted September 16, 2013 at 12:50 am | Permalink

            The solution to that is to make gears or wheels out of dead tissue, detached from the body and able to rotate freely. You’d want some sort of redundancy such as multiple wheels on one shaft, with newer ones replacing older ones as they wear out. The new ones would remain attached while they’re growing and only detach (and die) when they reach full size and begin to take up load.

            Not that I think we’re likely to find anything like that on Earth. There is, however, precedent for detached, freely moving (but not rotating) body parts in a rattlesnake’s rattle.

  15. conservationtrust
    Posted September 15, 2013 at 6:30 am | Permalink

    Hey, Bear, I don’t know if you get posts from this site, and if you do, I’m sure you’ve seen this, but thought you (and maybe Brett too) would find it interesting.

    Mama

  16. Posted September 15, 2013 at 5:16 pm | Permalink

    This looks much like a cross section of a fresh-water algae Charaphyta, microscopical fossils of which I found in copious amounts in rocks of Early Cretaceous age in the Yucca Formation in a Texas mountain range very near the Rio Grande years ago. We called them “gear fossils” while in the field. Long Live Science!


One Trackback/Pingback

  1. […] viral status; it was the subject of a report on NPR, and was even the topic of a post at another WordPress blog. The story is a one which involves the nymphs of a little Planthopper by the name of Issus. In […]

%d bloggers like this: