"The skate/ray mode I would call 'ambulatory swimming' whereas the axial/tail-based is more like 'spinal swimming,'" Dasen notes via email. This, according to the study findings, constitutes a conserved genetic program for walking.ĭasen says that neither "swimming" nor "walking" accurately describe the skate's movements, but perhaps this isn't too surprising given the human-centric nature of language. Many of these genes pop up in mammals as well - and that includes neural subtypes involved in the muscle control of bending and straightening limbs. This similarity impressed the researchers, but the similarities would go beyond movement.ĭasen and his colleagues employed RNA sequencing to study the expressed genes in the skate's motor neurons. The skate uses its large pectoral fins to swim and smaller pelvic fins to walk with alternating, left-right motions, much like the gait of a land animal. The little skate is also interesting because it's one of several ambulatory fish that "walk" across the seafloor. Travel back roughly 420 million years and you'll find a common ancestor of both skates and tetrapods. This cartilaginous fish might not be much to look at, but it's considered one of the most primitive vertebrates alive today. The researchers studied the neural circuitry of the little skate ( Leucoraja erinacea). In other words, much of the software was in place well before the walk-about hardware. The remarkable thing, says the team of researchers, is that the neural circuits involved in ambulatory limb control were already established millions of years before the first tetrapod strutted its stuff.
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