Abstract

Recent studies have revealed a variety of left–right asymmetries among vertebrates and invertebrates.In many species, left- and right-lateralized individuals coexist, but in unequal numbers (‘population-level’ lateralization). It has been argued that brain lateralization increases individual efficiency (e.g.avoiding unnecessary duplication of neural circuitry and reducing interference between functions),thus counteracting the ecological disadvantages of lateral biases in behaviour (making individualbehaviour more predictable to other organisms). However, individual efficiency does not require adefinite proportion of left- and right-lateralized individuals. Thus, such arguments do not explainpopulation-level lateralization. We have previously shown that, in the context of prey–predatorinteractions, population-level lateralization can arise as an evolutionarily stable strategy whenindividually asymmetrical organisms must coordinate their behaviour with that of other asymmetricalorganisms. Here, we extend our model showing that populations consisting of left- and right-lateralizedindividuals in unequal numbers can be evolutionarily stable, based solely on strategic factors arisingfrom the balance between antagonistic (competitive) and synergistic (cooperative) interactions.