(A) Dopamine synthesis pathway. Two DA synthesis genes, bas-1 and cat-2, are expressed in the male socket cells. Left images are DIC, right fluorescence. Sp = spicule, So = socket cells. Dorsal is up, anterior is to the left. Scale bar = 10 µM. (B) Images of a male expressing Pcat-2:YFP. Dorsal is up, anterior is to the right. Right, DIC images of the male tail. Left, fluorescent images of the male tail. Images of the spicule tips cut off are the same male 1 day later. Scale bar = 10 µM. (C) cat-2(lf) males insert at a low efficiency that is rescued by cat-2(+) in the ray neurons. Numbers above the bars are percentages, numbers at the x-axis indicate n. **p<0.005, ***p<0.0001, Fisher’s exact test. (D) Commencement times for males placed on the indicated concentrations of DA. Each dot represents one male and is a measurement of the time it took him, from the moment he was placed next to a 10 µM pad + hermaphrodites, to start backing along the hermaphrodite cuticle. n = 20 for each concentration. *p<0.05, one-way ANOVA with Bonferroni's correction.