Red shiners (Cyprinella lutrensis) have larger eyes in turbid habitats

The costs and benefits of investing in expensive sensory systems are shaped by environments that vary in the ease with which sensory information can be accessed. Fish provide an excellent model system in which to address questions of sensory evolution; while fishes rely heavily on vision, their visual environment is far more diverse and challenging than that of terrestrial animals. Turbidity, for example, alters the quantity of ambient light, its color, and the ability of animals to resolve borders of objects. Several comparative studies suggest that turbidity is associated with a reduction in the resources devoted to vision. Using these as a guide, we tested the prediction that turbidity and eye size would be negatively associated in populations of red shiners ( Cyprinella lutrensis (Baird and Girard, 1853)), a small-bodied cyprinid that is common and abundant in habitats spanning nearly the entire range of turbidity found in the Great Plains of the United States. We found that eye size was positively associated with turbidity, perhaps surprising given previous comparative work, but consistent with the finding that red shiners from turbid habitats display more intense nuptial coloration. This result highlights the need for further investigations of among-population variation to fully understand the mechanisms underlying sensory system diversity in animals.