Scientists have long thought that animals and humans need to exert pressure on the ground, air or water around them so as to push themselves forward when they move.
Findings of a new study, however, reveal that it isn't the case when it comes to jellyfish and lampreys - creatures known to move through water with unmatched efficiency using very low amounts of energy.
In a new study published in the in journal Nature Communications on Tuesday, researchers suggested that instead of pushing water rearward, these creatures "pull" themselves forward by generating a low pressure region in the water ahead of them.
Study researcher John Dabiri from the University of Stanford said that the low pressure is produced on top of the umbrella-shaped body of the jellyfish. The mechanism is different from an earlier understanding of these creatures' swimming dynamics as it was previously thought that they push against the water behind them.
To study the movement of these snake-like jawless fish, researchers observed the marine creatures in a tank where microscopic glass beads each measuring 10 micrometers across were placed in the water.
The tank was also outfitted with cameras and lasers that would highlight the movement of the glass beads when the animals swam, making it possible for the researchers to better trace the motion of the surrounding fluid when the creatures move.
Both animals were found sucking in the water ahead of them, which means that the jellyfish and the lamprey essentially suction their way when they move through waters.
Both animals employed coordinated undulations to produce vortexes in the surrounding water. The vortexes, which travel down the length of the creature, generate a low pressure region that creates forward pull, effectively sucking the animal as it swims through the water.
"Rather than pushing against the surrounding fluid, efficient swimming animals primarily pull themselves through the water via suction," the researchers wrote in their study. "These results suggest a rethinking of the evolutionary adaptations observed in swimming animals as well as the mechanistic basis for bio-inspired and biomimetic engineered vehicles."
The mechanism is being attributed to the highly efficient swimming capabilities of the creatures. If the animals propel themselves forward by pushing water back, they would waste plenty of energy.
"At the center of those vortexes you end up getting low pressure, just like in a hurricane or tornado you often will have low pressure in the middle of that rotating mass of air," Dabiri said. "In the case of the suction motion, it's possible to sort of slip past that water without leaving a lot of energy in your wake."