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. Resume : Les couts et avantages d'investir dans des systemes sensoriels plus importants sont determines par les milieux dans lesquels la facilite de l'acces a l'information sensorielle varie. Les poissons constituent un excellent systeme modele pour etudier les questions touchant a l'evolution sensorielle; ces animaux fortement dependants de leur vision evoluent dans des milieux visuels beaucoup plus varies et exigeants que les animaux terrestres. La turbidite, par exemple, modifie la quantite et la couleur de la lumiere ambiante, ainsi que la capacite des animaux aresoudre les contours des objets. Plusieurs etudes comparatives suggerent que la turbidite est associee aune reduction des ressources vouees a la vision. A la lumiere de ces etudes, nous avons verifie la prediction d'une relation negative entre la turbidite et la taille des yeux dans des populations d'ides americains anageoires rouges (Cyprinella lutrensis (Baird et Girard, 1853)), un petit cyprinide repandu et abondant dans des habitats couvrant presque toute la fourchette de turbidite observee dans la region des grandes plaines des Etats-Unis. Nous avons observe que la taille des yeux etait positivement associee ala turbidite, ce qui peut paraitre surprenant a la lumiere des etudes comparatives anterieures, mais qui concorde avec la constatation que les ides americains anageoires rouges issus d'habitats turbides presentent des couleurs nuptiales plus intenses. Ce resultat souligne la necessite d'etudes plus poussees des variations entre populations afin de mieux comprendre les mecanismes qui sous- tendent la diversite des systemes sensoriels chez les animaux. Mots-cles : Cyprinella lutrensis, ide americain a nageoires rouges, ecomorphologie, taille des yeux, turbidite, vision. (Traduit par la Redaction)