Phenotypic plasticity and social evolution

Eusocial insects – ants, termites, some wasps and some bees – typically live in colonies with one reproductive queen and thousands of sterile workers. This fascinating form of sociality has evolved from solitary, non-social ancestors. In this thesis, I investigate several aspects of the evolutionary transition from solitary ancestors to complex sociality. I investigate how eusociality with specialised queen and worker castes can evolve from solitary ancestors using evolutionary simulation models. I present experiments on the bee species Exoneura robusta, which has the special property that some individuals breed solitarily and some in social nests (“facultative sociality”), where one individual takes on a breeder role (“queen”) whereas the other subordinate individuals help her (“workers”). I investigate which environmental conditions trigger the bees to nest solitarily or socially. Furthermore, I investigate the molecular genetic differences between solitary bees and breeding and subordinate bees from social nests. I use simulation models to investigate the self-organised emergence and evolution of division of labour, where individuals are specialised on performing different tasks. Division of labour occurs in many biological systems, including eusocial insects. I present evolutionary simulations that investigate how sociality affects natural selection against senescence, and I study the evolution of extremely divergent lifespans between queens and workers. Overall, this thesis presents novel insights on several key aspects of social evolution, from the evolution of eusociality and facultative sociality, over the emergence and evolution of division of labour, to the evolution of ageing in social organisms.