THE EFFECTS OF WALLS, PATERNITY AND AGING ON SPERM MOTILITY

The measurement of sperm motility is critical when studying fertilizat ion kinetics and chemotaxis. Analysis of motility has traditionally be en carried out on cells in small fluid volumes on microscope slides. S everal theoretical treatments suggest that drag forces significantly a ffect flagellar motion within 10 sperm body lengths of the slide surfa ce. Understanding how sperm move in the absence of surface drag is cru cial when considering natural locomotory patterns. To examine the effe cts of solid surfaces, motile sperm from sea urchins (Arbacia punctula ta) were placed in a Plexiglas chamber (69mmx45mmx15.5mm; length x wid th x height). A system was constructed to minimize convective flow by limiting temperature differences within the chamber to less than 0.1 d egrees C. The movement of sperm was video-recorded at two levels: less than or equal to 100 mu m (3 body lengths) and 5 mm (150 body lengths ) below the chamber lid. When swimming speeds were measured using a co mputerized video motion-analysis system, a highly significant differen ce (P<0.0001) between cells at the two depths was found. Cells nearest the lid swam at 174.6+/-5.9 mu m s(-1) (mean +/- S.E.M.), whereas tho se farther away slowed to only 111.1+/-9.9 mu m s(-1) (mean +/- S.E.M. ). Swimming speed was also found to be significantly (P<0.01) affected by paternity, but not by sperm age. We conclude that viscous wall eff ects must be carefully considered in studies of sperm motility and che motaxis. The analysis of sperm on a microscope slide may substantially exaggerate swimming speed.