Chemical signals play a crucial role in the communication between sperm and egg that facilitates fertilization, but the identity of the signaling molecules involved remains unclear. In May 15 Journal of Experimental Biology, Jeffrey Riffell and colleagues from University of California, Los Angeles, show that the amino acid L-tryptophan is necessary and sufficient to promote recruitment of sperm to the surface of eggs in red abalone (Haliotis rufescens).

Riffell et al. investigated the behavioral responses of red abalone sperm to soluble factors released into seawater by conspecific eggs. They observed that sperm in proximity to individual live eggs swam significantly faster and oriented towards the egg surface. Bioassay-guided fractionation and chemical characterization by nuclear magnetic resonance spectroscopy indicated that the free amino acid L-tryptophan was the natural sperm attractant in H. rufescens (J Exp Biol 2002, 205:1439-1450).

"Elucidation of the sperm attractant for red...