Sperm adjust their swimming style to increase their chances of fertilizing an egg, reveals a new study.
Scientists discovered that they can change their “flagellar waveform” – how they oscillate their tails – to adapt to varying types of fluid within the reproductive tract.
The Australian research team says their findings suggest that each individual sperm adjusts its “power generation” to adapt and respond to the varying fluid dynamics, enabling it to swim against the flow.
Senior study author Doctor Reza Nosrati, of Monash University, said: “Our approach allowed us to investigate how variations in viscosity and shear rates affect sperm behavior at the single-cell level, which was not possible using traditional methods,”
He explained that biochemical and biophysical cues within the reproductive tract serve as “filters” against low-quality sperm and guidance mechanisms for high-quality sperm to navigate toward the egg.
For example, during sex, Dr. Nosrati said intensified mucus secretions within the oviduct stimulate fluid movement in the fallopian tube toward the uterus.
He explained that the flow helps prevent pathogens from invading the reproductive tract by flushing them down and simultaneously selects sperm capable of swimming against the flow toward the egg via a phenomenon known as rheotaxis.
But, until now, it has remained unclear how factors such as fluid flow interact to influence sperm flagellar beating behavior at the single-cell level.
For the new study, Dr. Nosrati and his team designed a “testing arena” for the sperm to observe their behavior under physiologically relevant conditions.
By tethering bull sperm in a microchannel, the researchers exposed the same individual sperm to a range of viscosities and shear rates, which refer to the rates of change in velocity at which one layer of fluid passes over an adjacent layer.
Using high-speed, high-resolution microscopy, the researchers quantified flagellar dynamics at 200 frames per second.
The findings, published in the journal Cell Reports Physical Science, showed that sperm flagellar waveforms are “primarily” influenced by viscosity.
The movements of sperm were less influenced by fluid flow in environments with lower viscosities.
The researchers said their findings suggest a potential increase in energy production and change in flagellar beating behavior under these specific conditions to possibly enable rheotaxis and a transition from circular motion to rolling motion.
Now, the team is refining the imaging techniques and experimental platform used for a follow-up study to examine free-swimming sperm under similar conditions.
Dr. Nosrati said: “It’s also crucial to better understand the importance of these media considerations with respect to sperm selection and fertilization.”
He added: “We plan to run an animal study to evaluate how such properties can influence fertilization and embryo development in assisted reproduction to inform future treatment strategies for better outcomes.”
Produced in association with SWNS Talker
