Visual ecology in challenging environments: How organisms evolve in extremes of light and adapt to shifting conditions

Sensory systems are under constant pressure from environmental changes, and vision offers a particularly rich lens to study adaptation. In this Special Feature, we present a collection of contributions that explore the roles of visual systems in extreme or dynamic environments. Too little light —In habitats ranging from caves to the deep sea, vision either becomes redundant and is lost, or undergoes striking morphological and molecular adaptations to maximize photon capture. The persistence of vision in dark deep‐sea ecosystems underscores the ecological role of bioluminescence as an alternative light source. Too much light —Excessive illumination, glare and UV radiation during the polar summer, in desert or snow‐covered habitats, drive the evolution of protective mechanisms, from UV‐filtering ocular media to behavioural strategies. Polar animals, such as reindeer, face the added challenge of coping with extreme seasonal variability in light conditions. Changing is challenging —While capable of remarkable plasticity, vision is vulnerable to abrupt or anthropogenic changes. Light pollution, turbidity and habitat alteration can disrupt communication, orientation and species boundaries, with cascading ecological effects. Coral reef fishes illustrate both the potential and limits of plasticity, while pigment functions reveal that visual systems are shaped by both visual and non‐visual demands, highlighting the need for integrative approaches to understand how changes may reshape visual ecology.