Relative cone opsin gene expression for Metriaclima zebra , given as a percentage of the total cone opsin expression as a function of age in days. The upper panel shows the expression of shorter wavelength sensitive opsins, which occur in single cones (SWS1 ●, SWS2b and SWS2a ◆). The lower panel shows the longer wavelength sensitive opsins, which occur in double cones (RH2b ● RH2a ▲ and LWS ◆). The RH2a expression is the sum of RH2aα and RH2aβ. This includes 13 sampled time points with two or three individuals sampled for ages <100 days and one or two individuals for ages >100 days. See Additional file 3 for curves fit to data.