The development of Chemoattractant plumes in complex 
flows and the role of the chemotactic strategies 
employed by sperm to navigate the plumes to fertilize 	
an egg

			Abstract

Many species of benthic invertebrates reproduce through the process of broadcast spawning. 
In this fertilization technique, the males release a cloud of sperm and the females release 
a cloud of eggs into the ambient flow. The two plumes are then brought close together by the 
dynamics of the flow. Once they are close enough, the sperm must then swim to the egg to 
successfully fertilize. Chemotaxis, the directed movement of an organism by a chemical, 
helps to guide the sperm to their conspecific egg. Each individual egg releases a plume of 
chemoattractant that the sperm then use to locate the egg. The plume of chemoattractant 
released from individual eggs was numerically modeled using the mechanisms of diffusion and 
advection. The diffusive plume was altered by the flow resulting from the presence of an egg 
in a shear flow. Both a steady flow, with a constant shear rate and orientation and unsteady 
shear flow, where both the direction and magnitude of shear rate varied in time, were 
modeled. This is reminiscent of the type of flow an egg would experience due to its small 
scale. We numerically modeled the sperm swimming behavior using several possible chemotactic 
strategies cited from passed studies. Within these strategies, the methods used to reorient 
the sperm's swimming path and alter the swimming speed are varied. Using a stochastic 
process, we are able to quantify the likelihood of fertilization for each chemotactic 
strategy within a variety of flows from different locations. The motility of the sperm turns 
out to be an evolutionary process that is able to mimic the process of diffusion, enhancing 
the ability of the two clouds of sperm and eggs to overlap to allow the sperm to fertilize 
the eggs.