Secret behind sperm's 'bendy' tail revealed

A sperm tail utilises interconnected elastic springs to transmit mechanical information to distant parts of the tail, helping it to bend and ultimately swim in a hostile environment towards an egg, a new study has found.
Previous studies showed that the sperm tail, or flagellum, was made up of a complex system of filaments, connected by elastic springs resembling a cylinder-like structure.
For many years, scientists believed that this system provided the sperm tail with a scaffold, allowing it to swim towards an egg.
However, new research at the University of York in the UK has shown through a mathematical model that this system is not only needed to maintain the structure of the tail, but is also vital to how it transmits information to very distant parts of the tail, allowing it to bend and move in its own unique way.

"Sperm flagella with this sort of internal structure can be seen in almost all forms of life," said Hermes Gadelha, from the York's Department of Mathematics.
Although the sperm tail has an internal structure that is conserved across most species - animal and human - they all create slightly different movements in order to reach an egg.

"This suggests that the tail's structure is not the whole story to how they make their distinct tail-bending motion," said Gadelha.
Researchers had previously developed a mathematical formula for the way in which sperm move rhythmically through fluid, creating distinct fluid patterns, but scientists now needed to understand what was going on inside the sperm tail that allowed them to move in this way.

To understand the structure of the tail, scientists examined how different parts of the tail bent by moving the tail of a dead sperm.
Surprisingly a movement that started near the head of the sperm, resulted in an opposite-direction bend at the tip of the tail, called the 'counterbend phenomenon'.
This suggests that mechanical information is transmitted along the interconnected elastic bands in order to create movement along the full length of the tail, researchers said.
The research was published in the Journal of the Royal Society Interface.