RIFFELL, J.A.*; KRUG, P.J.; ZIMMER, R.K.: Fertilization in the sea: Isolation and purification of abalone sperm chemoattractant

Sperm chemotaxis mediates fertilization in the free-spawning red abalone, Haliotis rufescens. In laboratory bioassays, sperm responded to a chemical attractant released by conspecific eggs and exhibited both activation and orientation. Computer-assisted video motion analysis demonstrated that sperm doubled their swimming speed in response to egg-conditioned sea water, and 90% of sperm oriented toward and recruited to live eggs. Using a flat-capillary assay, sperm exhibited chemotaxis towards the dissolved cue from eggs. Red abalone sperm exposed to egg-conditioned sea water from the green abalone, Haliotis fulgens, demonstrated no significant change in swimming speed or orientation in comparison to filtered sea water control. The red abalone chemoattractant was concentrated from egg-conditioned sea water using a C-18 column, yielding a single active fraction. Reversed-phase HPLC was employed and one major UV-absorbing peak was isolated that contained all bioactivity. The purified sperm attractant is about 200 Da, and is now being characterized by 1D and 2D NMR. Our results show that: (i) The attractant is similar in structure to the neurotransmitter, serotonin, and (ii) it is species-specific in its effect, and thus may be critical to reproductive isolation and speciation.