Principal component analyses (PCA) of eye measurements. We performed two different principal component analyses. One PCA was carried out using three variables (eye diameter, axial length, and lens diameter) and the resulting scatterplot of scores on PC 2 and PC 3 is illustrated in (a) and (b)). Panel (a) shows 95% confidence ellipses for nocturnal and diurnal groups; panel (b) demonstrates that elopomorphs occupy distinct areas in morphospace. The second PCA was carried out with five variables (adding largest and smallest pupil diameter; (c)). Vectors indicate magnitude and direction of loadings on PC axes. The plot of PC 3 against PC 2 shows in both analyses that nocturnal teleost reef fish (black circles) occupy different areas in morphospace than diurnal reef teleosts (yellow circles). Nocturnal species occupy a smaller area of morphospace. This is supported by the low combined variance of PC scores on all PC axes, calculated for the PCA with five variables, the most complete description of eye morphology available. Uneven sample size does not drive this pattern as shown by the resampling distribution for diurnal (yellow) and nocturnal (black) species. Ellipses represent 95% confidence ellipses for nocturnal and diurnal groups.