Temporal pattern of social aggregation in tadpoles and its influence on the measurement of lateralised response to social stimuli

Tadpoles of several species have been proven to prefer using the left hemifield during fixation of their own mirror images. The lateral bias typically emerges some minutes after the placement of the animals in the test apparatus. Here we checked whether such a temporal pattern was associated with lateralisation per se, or rather reflected temporal variations in social aggregation. We tested the temporal changes in tadpoles' movements directed towards conspecifics and other parts of the environment. We found that the propensity to move to make social aggregation only appears after about 5 min following placement in a novel environment and this corresponded quite well with the appearance of lateralisation, when tadpoles showed a higher probability of approaching a conspecific appearing on their left hemifield rather than on their right hemifield. These findings confirm, using natural conspecifics, evidence that in tadpoles, the left hemifield is better at detecting and directing approach responses to social stimuli. (C) 2002 Elsevier Science Inc. All rights reserved.