Fig. 9. Disruption of the tryptophan gradient around live eggs prevents navigation
by sperm. Individual red abalone eggs were placed in 400 µl of filtered sea
water (FSW) or the indicated test solution, after which sperm were added and
video-recorded for 30s. Representative swimming paths are shown as in
Fig. 1; the scale bar applies
to all panels. Polar plots show the vector mean direction of sperm swimming,
with angles measured relative to the egg surface (0°); the bar indicates
the vector mean length (r). (A) Sperm in FSW near the surface of a live
egg. (B) Sperm in the presence of the enzyme tryptophanase, which selectively
digests L-tryptophan as it diffuses from the egg. Enzyme treatment had no
effect on sperm viability. (C) Sperm in a uniform solution of 10-7
mol l-1 L-tryptophan. (D) Sperm in a uniform solution of
10-7 mol l-1 L-tyrosine. The tyrosine solution
controlled for any effects of elevating the concentration of an aromatic amino
acid in the sea water medium.
