A power amplification dyad in seahorses

Throughout evolution, organisms repeatedly developed elastic elements to
power explosive body motions, overcoming ubiquitous limits on the power
capacity of fast-contracting muscles. Seahorses evolved such a
latch-mediated spring actuation (LaMSA) mechanism; however, it is unclear
how this mechanism powers the two complementary functions necessary for
feeding: rapidly swinging the head towards the prey, and sucking water
into the mouth to entrain it. Here, we combine flow visualization and
hydrodynamic modeling to estimate the net power required for accelerating
the suction-feeding flows in 13 fish species. We show that the
mass-specific power of suction feeding in seahorses is ~3 times higher
than the maximum recorded from any vertebrate muscle, resulting in suction
flows that are ~8 times faster than similar-sized fish. Using material
testing, we reveal that the rapid contraction of the sternohyoideus tendon
can release ~72% of the power needed to accelerate the water into the
mouth. We conclude that the LaMSA system in seahorses is powered by two
elastic elements, the sternohyoideus and epaxial tendons. These elements
jointly actuate the coordinated acceleration of the head and the fluid in
front of the mouth. These findings extend the known function, capacity,
and design of LaMSA systems.