Figure 1. Experimental design for test of the effect of MitoTracker Green on competitive fertilisation success.

Each paired comparison involved three crosses between sperm from the same two competing males (focal and rival) and eggs from the same female. (A) Focal male’s sperm dyed to estimate X; (B) rival male’s sperm dyed to estimate Y; (C) both males’ sperm undyed and overall fertilisation rate, Z, measured. The focal male’s dyed success, X, was then compared to his undyed success, estimated as Z-Y.