Figure 2. Sperm characteristics differ between nesting males and sneakers.

Nesting male sperm are represented by red circles, sneaker male sperm by blue triangles. (a) Nesting male sperm exhibits significantly higher motility (per cent of sperm cells motile) than sneaker male sperm, and motility drops—as expected—for both male types over time. (b) Nesting males have higher curvilinear sperm velocity (VCL) than sneaker males shortly after activation (when fertilization is most likely to occur), but nesting male sperm velocity drops more quickly over time than sneaker male sperm velocity. Error bars indicate the s.e.m. The same qualitative pattern holds for other measures of sperm velocity (that is, straight line velocity (VSL) and average path velocity (VAP)). Statistical results are given in Table 2 (n=30, 10 per treatment).