This new study shows that it\u2019s possible to tune motor neurons for wildly different behaviors by tweaking a single protein. But motor neurons are just one piece of the movement puzzle. They\u2019re the last link in a chain that begins with circuits in the central nervous system known as central pattern generators, which generate the rhythmic patterns involved in walking or swimming. Those upstream circuits are better understood in other organisms, like zebra fish. In rattlesnakes, puzzling them out would be a next logical step.<\/p>\n

\u201cThe number-one missing link,\u201d Katz said, \u201cis how do you create the frequency for the rattle? Where does that come from?\u201d<\/p>\n

Chagnaud is eager to find out if a similar Stellschraube tunes motor neurons in another species feared for its bite. Like rattlesnakes, piranhas execute two rhythmic movements with radically different frequencies: swimming, with a frequency of up to six cycles per second, and vibrating their swim bladders at frequencies of up to 140 cycles per second to make noises that sound like barks, yips and drumbeats. However, unlike rattlesnakes, piranhas use the same section of their spine to control both movement types.<\/p>\n

\u201cI\u2019m curious to know, will it be KV7_{2\/3<\/sub>? We have no idea,\u201d Chagnaud said. \u201cDid evolution find the same solution to the same problem?\u201d<\/p>\n}

He has his doubts. Although he\u2019s hopeful about finding a similar mechanism, the surprising \u2014 and at times frustrating \u2014 discovery in rattlesnakes \u201cwas an eye-opener,\u201d he said. Evolution is not a human designer with a goal in mind. Its methods are mysterious, and its toolbox is vast. \u201cAnd you have very different screws that you can turn.\u201d<\/p>\n<\/div>\n

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