Population variation in lateralized eye use in the poeciliid Brachyraphis episcopi.

Differential use of each hemisphere of the brain for specific tasks is a widespread phenomenon that appears to have arisen in the early history of tetrapod lineage. Despite a high degree of conformity in the development of lateralization among the tetrapods, some variation exists. The mechanisms underlying this variation remain largely unresolved. We exposed fish from regions of high and low predation pressure to a series of visual experiences, including viewing an empty compartment, a novel object and a live predator. Fish from each region differed in their preferential use of each eye to view the scenes. For example, fish from high predation regions viewed a live predator by using their right eye, whereas fish from low predation sites showed no eye preference. These results suggest that the degree of lateralization varies between populations of the same species that have been exposed to different ecological/evolutionary pressures.