Figure 1.

Experimental design of the sperm competition assay. The same design is used to test for a role in ISC and CSP, by varying the identity of the first mated (GFP) male. The response phenotype is the proportion of progeny with green eyes; schematic expectations for each case are represented with pie charts. For genes involved in ISC (left-hand side), females are expected to produce proportionately more GFP offspring when mated to null/knockdown second males, compared with wild-type second males, as these individuals are less able to displace first male (GFP) sperm (owing to reduced offensive competitive ability). For genes involved in CSP (right-hand side), the same pattern is expected to hold, although the total proportions of green-eyed progeny are expected to be less than the respective crosses assessing ISC because of reduced compatibility in heterospecific crosses. (Online version in colour.)