The biological form of a mechanical gear was observed in nature for the first time in juvenile planthoppers (Genus: Issus), a common insect that can be found in gardens across Europe.
The insect has hind-leg joints with curved cog-like strips of opposing ‘teeth’ that intermesh, rotating like mechanical gears to synchronise the animal’s legs when it launches into a jump. The finding demonstrates that gear mechanisms previously thought to be solely man-made have an evolutionary precedent. [source]
Through a combination of anatomical analysis and high-speed video capture of normal planthopper movements, scientists from the University of Cambridge, led by Malcolm Burrows and Gregory Sutton, have been able to reveal these functioning natural gears for the first time. The findings were reported in the journal, Science (Vol. 341, Issue 6151).
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 precise synchronisation 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.
“By developing mechanical gears, the Issus can just send nerve signals to its muscles to produce roughly the same amount of force – then if one leg starts to propel the jump the gears will interlock, creating absolute synchronicity. [source]
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.
It’s not yet known why the Issus loses its 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. [source]
Read more about this fascinating research and discovery at the University of Cambridge.