Meeting Abstract

P3.85  Jan. 6  Plume dynamics and the mechanisms of sperm chemotaxis in turbulent flow RIFFELL, J.A.*; ZIMMER, R.K.; Univ. of Arizona; Univ. of California, Los Angeles jeffr@neurobio.arizona.edu

Chemical communication between sperm and egg is widely prevalent among taxa with divergent reproductive strategies, including terrestrial mammals and marine invertebrates. Sperm chemoattractants play a pivotal role in fertilization through mediating sperm-egg interactions and increasing gamete encounters. Surprisingly, no study has examined the influence of these signals under realistic conditions. Ubiquitous for all organisms is the presence of fluid motion at the scale of the sperm and egg. Fluid motion may have profound influence on gamete motility and sperm attractant distribution, but such effects are largely undescribed. This study investigated how fluid motion influences chemoattractant distribution around eggs, and the mechanisms by which sperm navigate to eggs under natural flow conditions. Our discovery of tryptophan as the natural attractant of abalone (Haliotis rufescens) sperm offered the opportunity to determine the navigational mechanism used by sperm. Numerical modeling demonstrated that fluid motion stretched the tryptophan plume around eggs, vastly increasing broadcast distances. Moreover, stretching of the plume caused shallow gradients to dominate plume structure, in contrast to the sharp gradients found in diffusion. Next, experimentally examining the kinetics of sperm behavior within a Taylor-Couette apparatus revealed that sperm use klinotaxis to orient and swim towards the egg. By integrating the changing concentration over a 200ms interval, sperm can navigate to a shallow gradient within a temporally and spatially dynamic fluid environment. Moreover, the concentration gradient, not concentration itself, modulated sperm trajectories. Thus, even at microscopic scales, physics tightly constrains the chemical signaling process, dictating sperm navigation.