Self-organized vortex phases and hydrodynamic interactions in Bos taurus sperm cells.

Area of Science:

• Physics of Living Systems
• Soft Matter Physics
• Biophysics

Background:

• Flocking behavior is a ubiquitous phenomenon in nature, observed across various biological scales.
• Understanding the mechanisms and purposes of collective motion is crucial for biological sciences.
• Bovine sperm cells exhibit complex dynamics in viscoelastic fluids.

Purpose of the Study:

• To investigate the collective dynamics of bovine sperm cells in a viscoelastic fluid.
• To explore the transition from disordered motion to flocking behavior induced by external stimuli.
• To compare experimental findings with theoretical models and single-cell properties.

Main Methods:

• Experimental observation of bovine sperm cell dynamics in a viscoelastic medium.
• Induction of flocking behavior using transient fluid flow pulses.
• Development and comparison with a computational model of persistently turning active particles.
• Mapping of collective motion phase diagrams based on cell density and motility.

Main Results:

• Bovine sperm cells do not spontaneously flock but can be induced into a long-lived flocking phase.
• Induced flocking exhibits similarities to spontaneous polar flocking, including giant number fluctuations and density correlations.
• A self-organized global vortex state was observed, and a phase diagram of collective motion was established.
• Experimental phase boundaries were successfully predicted using single-cell properties and a computational model.

Conclusions:

• Transient fluid flow can induce flocking behavior in bovine sperm cells, mimicking spontaneous flocking phenomena.
• Collective dynamics are influenced by cell density, motility, and momentum conservation.
• The study provides a framework for predicting collective behavior from individual cell properties, with potential applications in fertility evaluation.