More than three centuries ago, Anton van Leeuwenhoek discovered the human sperm using the compound microscope he had invented. He observed that the sperm has a tail which lashes from side to side to make the sperm move forward in a snake-like fashion. Since then, this knowledge has been passed down for centuries until recently this observation has been revealed to be an optical illusion.
A team of researchers from Bristol and Mexico used 3D microscopy and advanced mathematical analyses to realize that the sperm’s tail actually moves in one direction. Logically, movement in only one direction results in a circular motion. However for the sperm to reach the egg, the head or body rotates in a corkscrew-like motion in the opposite direction, resulting in a straight forward movement.
“We were not expecting to find what we found,” says Hermes Gadêlha, head of the Polymaths Lab at University of Bristol and lead author on the study. “The aim of the project was ‘blue sky’ (or broad) research, to understand how sperm moves in 3D. And the result has completely changed the belief system that we have.”
The research team used a combination of 3D microscope and a piezoelectric device to study the movement of the sperm at the submicron level. In addition, a high-speed camera which could record over 55,000 frames per second was used to gather the needed information.
From the time of Leeuwenhoek, sperm movement had been observed using 2D microscopes. This created an illusion of the tail moving from side to side symmetrically. But this new breakthrough has shown that the sperm moves like a spinning top, rotating around its own axis. This makes it to roll like playful otters.
“What nature is telling us is that there is more than one way to achieve symmetry,” says Gadêlha. “Sperm use asymmetry to create symmetry.”
Other organisms such as the mouse and rat sperm and the flagella of Chlamydomonas, a green algae have asymmetric movements. However, this new discovery can be used to study male infertility through the biology of sperm motility. It can also be used for further advancements in the natural reproduction of humans.