Abstract

Evidence of left–right asymmetries in invertebrates has begun to emerge, suggesting that lateralization
of the nervous system may be a feature of simpler brains as well as more complex ones. A variety of
studies have revealed sensory and motor asymmetries in behaviour, as well as asymmetries in the nervous
system, in invertebrates. Asymmetries in behaviour are apparent in olfaction (antennal asymmetries) and
in vision (preferential use of the left or right visual hemifield during activities such as foraging or escape
from predators) in animals as different as bees, fruitflies, cockroaches, octopuses, locusts, ants, spiders,
crabs, snails, water bugs and cuttlefish. Asymmetries of the nervous system include lateralized position
of specific brain structures (e.g., in fruitflies and snails) and of specific neurons (e.g., in nematodes). As in
vertebrates, lateralization can occur both at the individual and at the population-level in invertebrates.
Theoretical models have been developed supporting the hypothesis that the alignment of the direction of
behavioural and brain asymmetries at the population-level could have arisen as a result of social selective
pressures, when individually asymmetrical organisms had to coordinate with each other. The evidence
reviewed suggests that lateralization at the population-level may be more likely to occur in social species
among invertebrates, as well as vertebrates.