The dynamics of reproductive dominance in dinosaur ants

Social insects represent one of the pinnacles of social
evolution, and their huge ecological success may be
attributable to the sophisticated division of labour and
conflict resolution observed in their societies. Eusocial
societies exist along a continuum from facultative and
primitive (simple) societies in which subordinates retain
reproductive totipotency into adulthood, to advanced societies in which the sterile worker caste are committed
to their subordinate role. Queenless ponerine ants are
unusual, however, exhibiting a simple social structure but
having recently diverged from an advanced ancestor. They
therefore represent a powerful model system for understanding the roles of evolutionary history, ecology
and sociality on behavioural and physiological division of
labour. Here, I investigate the influence of reproductive
dominance on division of labour and social cohesion in
the queenless dinosaur ant, Dinoponera quadriceps.
I also present the first description of their natural foraging and nesting ecology. Finally, I investigate the
physiological control of division of labour and behavioural
plasticity, and explore the relative contribution of
conserved and novel genes in the evolution of simple society
in this species. Dinosaur ants exhibit remarkable behavioural plasticity despite their advanced ancestry;
individual behaviour is strongly influenced by future
reproductive prospects and learned aspects of the social
environment. They exhibit a discontinuous social hierarchy,
in which the reproductive female is transcriptionally
distinct from her subordinates, with the largest expressional differences observed in relation to reproductive physiology. Their advanced ancestry is evident
both behaviourally and transcriptionally; they exhibit few
differences in gene expression within the ancestral worker
caste as well as advanced behaviours such as allogrooming,
which has been co-­‐opted for a role in social cohesion
since their reversion to simple society. Dinosaur ants reveal the relative influences of social behaviour and evolutionary history in shaping the behavioural and physiological characteristics of eusocial societies.