Meeting Abstract

S4.1  Wednesday, Jan. 5  The ‘Neuroecology’ of Sperm-Egg Interactions ZIMMER, Richard; Univ. of California, Los Angeles z@biology.ucla.edu

Chemically mediated behavior is a key component of sperm-egg dynamics in habitats ranging from the turbulent ocean to the mammalian reproductive tract. Recent discoveries of the sperm attractants, bourgeonal in Homo sapiens and L-tryptophan in abalone (Haliotis rufescens), have bridged the gap between molecular biology and fertilization ecology. In humans, a bourgeonal-sensitive, olfactory receptor protein (OR1D2) is expressed exclusively on sperm membrane. Thus, sperm have a “nose”. The receptor acts through a G-protein-coupled cAMP transduction pathway in regulating calcium uptake and sperm chemotactic responses. In abalone (a large marine mollusk), sperm detect a shallow concentration gradient that develops when tryptophan is released by an egg. These natural attractant plumes change their sizes and shapes in response to physical and chemical characteristics of the environment. Performance-maximizing shears are those most closely simulating flows in native spawning habitats. Empirical findings for sea urchins (Arbacia punctulata) and abalone suggest, further, that chemical signaling is a cheap evolutionary alternative for increasing egg target size without enlarging cytoplasm and/or cell volume. Moreover, endogenous signaling pathways appear co-opted for external communication by gametes as an adaptation to increase reproductive success. Egg-derived attractants can determine the outcomes of mate competitions, act as beacons for promoting male-female gamete encounters, or both. The exact function depends on ecological and evolutionary contexts, on the relative importance of dissolved versus contact (membrane recognition proteins) cues, on hydrodynamic processes that establish gamete distributions, and on fluid shears that either promote or suppress gamete behavioral interactions within the natural world.