Figure 1.

A single block of the cross-classified design to test effects of ovarian fluid (OF) on competitive fertilization success. The genetic identity of females within each block is standardized by using eggs from a single female (eggs_stand) across all four crosses (note that eggs_stand are bathed in OF from two different females). A different standard female was used in each block of the design. The competitive fertilization ability of sperm from two focal males (sperm₁ and sperm₂) was tested against sperm from a single standardized rival male (sperm_stand), so that sperm competitiveness across different female OF backgrounds was not influenced by stochastic effects attributable to differences among non-focal rival males. Again, different focal and standard males were used in each block. Each competitive fertilization trial was performed in replicate, thus generating eight in vitro fertilization trials for each block. Paternity success from each cross was estimated using microsatellite DNA markers (see main text).