Abstract

During the last years, studies on bilateral asymmetry have substantially increased. However, in the literature exists a clear trend toward the study of the fluctuating asymmetry over directional asymmetry and anti symmetry, because it has been assumed that the first one reflects the developmental instability facing environmental or genetic disruptions. Anyway, it is important to study both directional asymmetry and anti symmetry, because they would provide information about ontogenetic and evolutionary processes of fluctuating asymmetry. Only exploratory studies have been made in bivalves in spite of their potential use as a tool in monitoring the stress levels in natural populations and as an indicator of the Darwinian fitness. In this review the significance of the bivalve bilateral asymmetry and factors that regulate the asymmetric components in an evolutionary context are enhanced. We emphasize the necessity of simultaneous studies of the three types of bilateral asymmetry at different geographical scales in the range of the distribution of the species, to determine the ecological and evolutionary patterns and the main factors that cause it