Exploring the regulatory role of behaviour and genome architecture in the socially polymorphic ant, Leptothorax acervorum

Eusocial species show incredible variation in all aspects of social living, which has facilitated their ecological success. Investigating the mechanisms which regulate variation in social traits is an important goal for evolutionary biology, since understanding fundamental mechanisms underpinning variation can inform social evolutionary theory. In this thesis, I investigate aggressive behaviour and genome architecture as essential mechanisms in regulating variation in the polymorphic social phenotype of the multiple queened ant species L. acervorum. I investigated the role of enforcement behaviour in maintaining reproductive skew in functionally monogynous colonies. I show that in the absence of worker aggression (enforcement), functionally monogynous queens continue to engage in highly aggressive interactions and, crucially, high colony skew was not affected. Furthermore, I show that low skew is not affected by aggressive worker enforcement in polygynous colonies. Therefore, enforcement behaviour is likely to be important in regulating skew in functionally monogynous colonies but not in polygynous colonies, where potentially the loss of sensitivity to enforcement may be an evolved response to fitness benefits associated with the polygynous social phenotype. Furthermore, I investigated the role of genome architecture in regulating variation between the two social phenotypes. I scanned the genomes of four populations (two polygynous and two functionally monogynous) for extreme population differentiation (FST) at SNP loci, which were associated with a difference in the social phenotype. I found a large (6.2Mb) contiguous region associated with different social phenotypes (the social region), which mapped to LG2 on the S. invicta linkage map. The social region displayed some similarities with the social chromosomes in S. invicta and F. selysi. Furthermore, the region contained potential gene candidates, such as odorant binding proteins, which have been associated with divergent social phenotypes in S. invicta. The work presented in this thesis highlights the importance of different mechanisms, both behavioural and genomic, in regulating variation in fundamental social traits. Furthermore, it demonstrates the importance of understanding how mechanisms can bridge the gap between genotype and phenotype.