It’s a known fact that sperms generally swim by beating or rotating their soft tails. However, City University of Hong Kong researchers have discovered that ray sperms moved by rotating both their tail and their head. To investigate the motion pattern further, researchers have demonstrated that technique using a robot.
The study has expanded the knowledge of how microorganisms move and provided inspiration for robot engineering design. Researchers defined a new and peculiar motion mode for ray sperms called “Heterogeneous Dual Helixes (HDH) model.” Interestingly, the motion used by the ray sperms was an accidental discovery.
The team was researching an artificial insemination technique for the farming of cartilaginous fishes such as sharks and rays. The team explains that cartilaginous fishes can be used as a “factory” to produce antibodies against diseases such as COVID-19. The team wanted to develop an artificial insemination technique to farm them as high-value aquaculture.
During the process, the team observed the unique structure and swimming motion of ray sperms under the microscope. Researchers found that the ray sperm’s head is a long helical structure rather than being round and it rotates along with the tail when swimming. The sperm consists of heterogeneous helical sections, including a rigid spiral head and a soft tail connected by a mid-piece providing energy for rotational motion.
The head of the ray sperm is the container for the genetic material and helps facilitate propulsion along with the soft tail. Researchers say the head contributes about 31 percent of the total propulsive force, which is the first recorded head propulsion in any known sperm. Thanks to the motion of the head, the motion efficiency of the ray sperm is higher than other species that are only driven by the tail. Scientists on the project also found that the ray sperms have bi-directional swimming capability allowing them to swim forward and backward as needed.