Increased group size promotes task specialization in a normally solitary halictine bee

Division of labour is a fundamental property of animal groups; how it is generated and evolves is, therefore, of central importance to sociobiology. Self-organizational models suggest (1) that division of labour can emerge spontaneously at the origin of group living and (2) that increased group size further promotes task specialization. We examined the emergence and scaling of division of labour in an evolutionarily incipient social system: forced associations of the normally solitary halictine bee Lasioglossum (Ctenonomia) NDA-1. A division of labour between nest excavation and guarding arose in pairs and in groups of four bees, with individuals in larger groups exhibiting higher degrees of task specialization. Task differentiation may be facilitated by intrinsic behavioral variability and/or spatial organization. Our results support the hypotheses that division of labour can self-organize at early stages of social evolution and that greater individual specialization is an emergent consequence of increased group size.