Enhanced schooling performance in lateralized fishes

Abstract

The occurrence of functional left-right cerebral asymmetries has been documented in a wide range of animals, suggesting that the lateralization of cognitive functions enjoys some kind of selective advantage over the bilateral control of the same functions. Here, we compared schooling performance of fishes with high or low degree of lateralization, which were obtained through selective breeding. Schools of lateralized fishes moving in a novel environment showed significantly more cohesion and coordination than schools of non-lateralized (NL) fishes. Pairs of fishes lateralized in opposite directions were as efficient as pairs of same laterality, suggesting that the performance of lateralized fishes derives from a computational advantage rather than being the consequence of a behavioural similarity among schoolmates. In schools composed of both lateralized and NL fishes, the latter were more often at the periphery of the school while lateralized fishes occupied the core, a position normally safer and energetically less expensive.

Figure 1

Measures of schooling efficiency (average and s.e.m.) in pairs of lateralized or NL fishes. (a) Inter-individual distance (snout to snout); (b) the degree of alignment of the school (angle between the two body axes); (c) schooling index, computed as the geometric combination of the two previous measures. Fishes were obtained from selective breeding experiments. Pairs of fishes selected to turn left (LL, n=17) or right (RR, n=18) in front of a model predator were compared with pairs of fishes with opposite lateralization (MixL, n=22) and with pairs of NL fishes (NN, n=37).