Plastic fish in troubled waters: Behavioural, developmental and eco-evolutionary aspects of visual system diversity in East African cichlids

Understanding the mechanisms that generate the outstanding biological diversity on our planet has been extensively studied. However, to this date many questions remain unresolved. A fundamental process that produces biodiversity is divergent adaptation: here populations diversify by adapting to different environmental conditions. In this project, I investigated the role of the sensory system in this process, as sensory perception is critical for survival and reproduction: How do sensory systems adapt to local environments and (how) does individual flexibility contribute to this process? The fish visual system provides an excellent opportunity to study these questions as it shows extensive variation among species/populations. Fish inhabit different visual environments, as a result of wavelength-dependent light attenuation in water. There are strong indications that adaptation of the visual pigments in fish eyes plays a role in the origin and persistence of species. In this thesis I focused on cichlid fish, one of the most species-rich vertebrate families. At the level of visual pigment molecular composition, I showed that closely related species deal in different ways with variation in light conditions and differ in their plastic response to experimental light treatments. Despite these differences, fish did not go where they saw best in a behavioural choice experiment. Instead, they had a general preference for blue light. Finally, in a comparative analysis I found no evidence that diversification rates depend on the visual environment of a lineage. Together, my findings highlight that vision rapidly diverges between species/populations, impacts behaviour and is also influenced by individual flexibility.