The evolution of caste plasticity and caste dimorphism in insect societies.

The evolution of sociality in ants, bees and wasps is a prime example of a major transition in evolution, where individuals went to live in societies characterised by the presence of an advanced reproductive division of labour. In primitively eusocial species, the allocation to reproductive and nonreproductive roles in the colony is highly plastic, while in more advanced eusocial species, the queen and worker castes are morphologically distinct. Recently, it was shown that the caste plasticity in a primitively eusocial ant species showed reversible changes in brain volume in function of reproductive role, with breeding females reducing their brain size to allow for an increased investment in egg production. In the present project, we will study the occurrence of such caste plasticity in function of reproductive role across a wider range of primitively and advanced eusocial temperate and Neotropical ants, bees and wasps using a combination of state-of-the-art genomic, light sheet fluorescence microscopy (LSFM) brain imaging and behavioural experiments. This will allow us to study shifting patterns in the evolution of behavioural plasticity in eusocial insects, including possible tissue trade-offs and changes in the modularity in brain gene expression patterns. In addition, we will study how pre-existing gene regulatory ground plans in primitively eusocial wasps could have laid the basis for the evolution of morphologically defined castes in advanced eusocial wasps.