Fluid viscoelasticity promotes collective swimming of sperm

Chih-Kuan Tung,Susan S Suarez,Benedict Harvey,Alyssa G Fiore,Mingming Wu,Florencia Ardon,Chungwei Lin

doi:10.1038/s41598-017-03341-4

Abstract

From flocking birds to swarming insects, interactions of organisms large and small lead to the emergence of collective dynamics. Here, we report striking collective swimming of bovine sperm in dynamic clusters, enabled by the viscoelasticity of the fluid. Sperm oriented in the same direction within each cluster, and cluster size and cell-cell alignment strength increased with viscoelasticity of the fluid. In contrast, sperm swam randomly and individually in Newtonian (nonelastic) fluids of low and high viscosity. Analysis of the fluid motion surrounding individual swimming sperm indicated that sperm-fluid interaction was facilitated by the elastic component of the fluid. In humans, as well as cattle, sperm are naturally deposited at the entrance to the cervix and must swim through viscoelastic cervical mucus and other mucoid secretions to reach the site of fertilization. Collective swimming induced by elasticity may thus facilitate sperm migration and contribute to successful fertilization. We note that almost all biological fluids (e.g. mucus and blood) are viscoelastic in nature, and this finding highlights the importance of fluid elasticity in biological function.

Highlights

In biology, collective movement spontaneously occurs in diverse systems ranging from swimming bacteria[1], swarming insects[2], and flocking birds[3,4,5] to dancing crowds in a rock concert[6]
We report a collective swimming pattern of sperm enabled by the elastic component of complex fluids
This result highlights the significance of viscoelastic properties of fluid in assisting cell – cell interaction, and as such cells are mechanically inter-linked through the viscoelastic fluids to form organized swimming patterns

Summary

Introduction

Collective movement spontaneously occurs in diverse systems ranging from swimming bacteria[1], swarming insects[2], and flocking birds[3,4,5] to dancing crowds in a rock concert[6]. In all of these systems, one finds that the interactions of the constituents lead to collective group behavior, similar to phase transitions in physics, in which order emerges by either lowering random thermal fluctuations (temperature) or increasing the inter-particle coupling[7, 8]. Our observation provides an evolutionary pathway for the development of sperm cooperation observed in several species of rodents[26, 27]

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Results

Conclusion