Robust Sensory Traits Across Light Habitats: Visual Signals but Not Receptors Vary in Centrarchids Inhabiting Distinct Photic Environments

Visual communication in fish is often shaped by their light environment, which influences both sensory (e.g., eye size, opsin gene expression) and signalling traits (e.g., body reflectance). This study explores the phenotypic variation in the visual communication traits of six species of centrarchids (Centrarchidae) inhabiting two contrasting light environments. We measured morphological, molecular and signalling traits to determine their variation across photic conditions. Our findings reveal significant interspecific variation in sensory traits but no consistent phenotypic variation between light environments. Centrarchids showed robust visual systems with green-sensitive rh2 and red-sensitive lws opsin genes representing the main chromatic channels, with their expression remaining largely unaffected between distinct light habitats. We also found significant molecular evolution in the visual opsin genes, although these changes were not associated with environmental conditions. However, body reflectance displayed species-specific responses to environmental conditions, suggesting that signalling traits may be more flexible than sensory traits. Overall, our results challenge the generality of the current paradigm in visual ecology, which portrays visual systems in fish as highly tunable owing to photic conditions. Our study highlights the potential evolutionary or developmental constraints on centrarchid visual systems and their implications for adaptability to various habitats and novel environmental threats.