Sexual dimorphism and variation between Drosophila species and strains in rhodopsin mRNA expression. A Variation in the expression of rh3 mRNA relative to the expression of rh3 and rh4 combined (rh3:rh3 + 4), the rh3 index. B Variation in the expression of rh5 mRNA relative to the expression of rh5 and rh6 combined (rh5:rh5 + 6), the rh5 index. Boxplots represent the variation between four technical replicates within each of biological replicates a and b for each strain. Asterisk, missing data; F, female; M, male; dark blue, female D. mauritiana; light blue, male D. mauritiana; dark green, female D. simulans; light green, male D. simulans; dark violet, female D. melanogaster; violet, male D. melanogaster.