Eye as a key element of conspecific image eliciting lateralized response in fish.

Visual lateralization in different aspects of social behaviour has been found for numerous species of vertebrates ranging from fish to mammals. For inspection of a shoal mate, many fishes show a left eye-right hemisphere preference. Here, we tested the hypothesis that in fish, there is a key cue in the conspecific appearance, which elicits lateralized response to the whole image of the conspecific. In a series of eight experiments, we explored eye preferences in cryptic-coloured Amur sleeper, Perccottus glenii, fry. Fish displayed left-eye preferences at the population level for inspection of a group of conspecifics, their own mirror image, and a motionless flat model of a conspecific. In contrast, no population bias was found for scrutinizing an empty environment or a moving cylinder. When fry were showed a model of a conspecific in a lateral view with the eye displaced from the head to the tail, they again showed a significant preference for left-eye use. On the other hand, 'eyeless' conspecific model elicited no lateralized viewing in fry. Finally, the left-eye preference was revealed for scrutiny of the image of a conspecific eye alone. We argue that in Amur sleeper fry, eye is the element of the conspecific image, which can serve as a 'key' for the initiation of lateralized social response. This key element may serve as a trigger for the rapid recognition of conspecifics in the left eye-right hemisphere system. Possible causes and advantages of lateralized perception of social stimuli and their key elements are discussed in the context of current theories of brain lateralization.

An eye for a worm: lateralisation of feeding behaviour in aquatic anamniotes.

Some animals, notably birds, preferentially approach and capture food items in their right visual field. However, this lateralised behaviour has not been studied extensively in anamniotes. Here we test eye preference during feeding for a fish, (Perccottus glenii; Teleostei, Perciformes), a newt, (Pleurodeles walti; Amphibia, Caudata), and a frog, (Xenopus laevis; Amphibia, Anura) using a test chamber that assesses reaction to visual stimuli while blocking olfactory and mechanical input. Both the fish and the newt showed right preferences in reactions to food items, but the frog did not. Our data extend our knowledge of the lateralised behaviours of vertebrates and are the first record of lateralised prey capture in a caudate amphibian. This finding dates back the history of the common pattern for visual lateralisation in vertebrates to Devonian, when the fish and quadruped lineages diverged.