Flagellar Cooperativity and Collective Motion in Sperm

Abstract

Sperm have thin structures known as flagella whose motion must be regulated in order to reach the egg for fertilization. Large numbers of sperm are typically needed in this process and some species have sperm that exhibit collective or aggregate motion when swimming in groups. The purpose of this study is to model planar motion of flagella in groups to explore how collective motion may arise in three-dimensional fluid environments. We use the method of regularized Stokeslets and a three-dimensional preferred curvature model to simulate groups of undulating flagella, where flagellar waveforms are modulated via hydrodynamic coupling with other flagella and surfaces. We find that collective motion of free-swimming flagella is an unstable phenomenon in long-term simulations unless there is an external mechanism to keep flagella near each other. However, there is evidence that collective swimming can result in significant gains in velocity and efficiency. With the addition of an ability for sperm to attach and swim together as a group, velocities and efficiencies can be increased even further, which may indicate why some species have evolved mechanisms that enable collective swimming and cooperative behavior in sperm.

Frequency-dependent viscosity of salmon ovarian fluid has biophysical implications for sperm–egg interactions

“…Also, until the shear thickening behaviour of the ovarian fluid is confirmed, the complete picture of how sperm swim in ovarian fluid is not clear. Currently, all the modelling approaches published, have assumed exclusively a shear-thinning fluid at smaller shear flows such as those experienced by sperm in the genital tract of internally fertilising animal models ( Guasto et al, 2020 ; Kumar and Ardekani, 2020 ; Simons and Rosenberger, 2021 ). In fact, recent findings have evidenced how the elliptical trajectories of the sperm change as a consequence of different external shear flows and with changing ratios between the elastic and the viscous predominancies within the fluid, where the length and the stiffness of the flagellum can have profound influence on its swimming efficiency ( Kumar and Ardekani, 2020 ).…”

Locomotion of bovine spermatozoa during the transition from individual cells to bundles

“…Synchronized flagella not only enhance the swimming speed of sperm cells but also consume less energy than desynchronized flagella ( 15 , 16 , 18 , 53 ). This locomotion strategy of sperm cells can be further implemented into the design and development of multiflagellated soft microrobots that can generate increased propulsive thrust to overcome greater flow rates of bodily fluids ( 60 ).…”

“…In some higher organisms, e.g., bulls ( 8 ), rodents ( 9 , 10 ), and insects ( 11 ), spermatozoa are found to assemble into bundles. The assembly is an efficient locomotion strategy at a low Reynolds number, which has been numerically ( 12 – 16 ) and experimentally ( 8 – 10 ) demonstrated to increase the swimming speed of spermatozoa, whereby their fertilizing ability is favored ( 10 , 17 ).…”