The ontogenetic saga of a social brain

Queen and worker honeybees differ in a number of life-history traits, including the size of certain brain regions, such as the mushroom bodies (MBs), which are larger in workers. However, during the larval period, the differential feeding offered to queens promotes faster brain development. As a result, members of this caste have larger brains than workers. This developmental process is accompanied by the higher expression of several neurogenic genes. Nonetheless, a caste-specific shift in relative brain growth occurs during the next developmental stage. The suggested molecular underpinnings of this phenomenon are variations in hormonal environments, which may mediate higher cell death rates in the queen's brain than in the workers'. The brain development of this highly eusocial bee is thus a paradoxical case that may represent an evolutionary by-product of the reproductive division of labour in species with female size diphenism.