THE need for speed forced tuna and certain sharks to independently evolve remarkably similar bodies.
The similarity between the body shapes and swimming techniques of tuna and shark species like the mako and great white has long been attributed to their shared lifestyle. 鈥淭hey prey on fast-moving fish so they have to be capable of high sustained speed and explosive bursts of speed,鈥� says Jeanine Donley, a biomechanics expert at Scripps Institute of Oceanography in San Diego, California. Both types of fish have similar profiles, and use their tails for propulsion while their bodies stay rigid.
But this resemblance is much more than skin deep, say Donley and her colleagues, who compared known tuna data with new studies of mako shark physiology (Nature, vol 429, p 61). They found that both types of fish have muscles for sustained swimming that can move independently of surrounding skin and tissue, and transmit muscle force through unusually long tendons. This allows these creatures to channel power directly to their tails. These adaptations are part of locomotor systems that are unlike virtually all other fishes, say the researchers.
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