Correlating relative light sensitivity to retinal visual gene expression patterns in three African cichlid fish species

Visually guided behaviour requires adequate visual sensitivity. Hypotheses on the evolution of vertebrate visual systems largely rely on the assumption that the retinal expression pattern of visual genes is a major determinant of visual sensitivity. However, data on how visual gene expression relates to visual sensitivity and, ultimately, behaviour are equivocal. Here, we correlate relative visual sensitivity to light of different wavelengths with visual gene expression patterns, quantified at various times after the behavioural trials, for three species of African cichlids, raised in different light treatments. To estimate visual sensitivity to different wavelengths, we used the dorsal light response, where fish orient their dorsoventral axis towards the direction of the greatest perceived intensity of incoming light. We found light-treatment-dependent and interspecific variation in relative visual sensitivity. However, at the species and treatment levels, visual gene expression patterns were not indicative of relative visual sensitivity, whereas we did find such correlations at the individual level. Our results indicate that differences in visual sensitivity of cichlid fish cannot be explained by visual gene expression patterns alone, as it may not reflect actual retinal pigment composition and density. In addition, post-retinal (neural) processes might play an important, but as yet unknown, role.