Biomixing by chemotaxis and efficiency of biological reactions: the critical reaction case

TL;DR

This paper investigates how chemotaxis influences biological reaction efficiency, especially in the critical quadratic reaction case, revealing that chemotaxis significantly accelerates reactions and enhances their effectiveness.

Contribution

It extends previous models by analyzing the quadratic reaction case, demonstrating chemotaxis's crucial role in reaction efficiency and timescale independence from coupling strength.

Findings

Chemotaxis accelerates reaction timescales.

Reaction can complete without chemotaxis, but very slowly.

Chemotaxis makes reaction efficiency independent of coupling parameter.

Abstract

Many phenomena in biology involve both reactions and chemotaxis. These processes can clearly influence each other, and chemotaxis can play an important role in sustaining and speeding up the reaction. In continuation of our earlier work, we consider a model with a single density function involving diffusion, advection, chemotaxis, and absorbing reaction. The model is motivated, in particular, by the studies of coral broadcast spawning, where experimental observations of the efficiency of fertilization rates significantly exceed the data obtained from numerical models that do not take chemotaxis (attraction of sperm gametes by a chemical secreted by egg gametes) into account. We consider the case of the weakly coupled quadratic reaction term, which is the most natural from the biological point of view and was left open. The result is that similarly to higher power coupling, the chemotaxis plays a crucial role in ensuring efficiency of reaction. However, mathematically, the picture is quite different in the quadratic reaction case and is more subtle. The reaction is now complete even in the absence of chemotaxis, but the timescales are very different. Without chemotaxis, the reaction is very slow, especially for the weak reaction coupling coefficient. With chemotaxis, the timescale and efficiency of reaction are independent of the coupling parameter.