The role of visual adaptation in cichlid fish speciation

Aquatic environments are well-suited for studying visual adaptation; light attenuation creates distinct photic environments, to which vision-dependent species must adapt. In Lake Victoria, Pundamilia cichlids with blue vs. red male coloration co-occur at many locations. The species are depth-segregated, occupying different visual habitats, have different colour vision properties, and females exert species-specific mate preferences for male colour. Correspondence between these factors implicates divergent sensory drive as the mechanism of speciation. Here, I experimentally test this hypothesis, examining the link between vision and behaviour. We manipulated visual system development by rearing fish in environments mimicking the light conditions of Lake Victoria and then tested for variation in behaviour and visual system properties. Light treatments influenced female preference for blue vs. red males, while male coloration did not change. Light treatments also influenced the expression of colour sensitive pigments in the eye, but we could not establish a causal link between pigment expression and preference. Possibly, visual pigment genotype is more important for female preference. This is in line with the results of foraging tests, in which fish performed better when tested in light conditions natural to each species. Finally, field surveys revealed geographic variation in pigment expression across populations, that did not align with species differences in visual pigment genotype and female preference. I conclude that visual perception influences cichlid behaviour, but that different components of the visual system, i.e. pigment gene sequence and expression, may play different roles in Pundamilia adaptation and speciation