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Quantitative Genetics of Caste in Social Insects

Final Report Summary - GENETICS OF CASTE (Quantitative Genetics of Caste in Social Insects)

The social insects are established model systems for the study of social evolution and are emerging model systems for studying the evolution of aging, behaviour, epigenetics, and complex social systems. However, we know relatively little of the genetic architecture underlying any social insect traits. This is a major limitation because the genetic architecture underlying traits determines how traits respond to selection. Furthermore, understanding the genetic basis of phenotypes is a fundamental goal of evolutionary biology because it elucidates how complexity has been constructed through evolution. The main reason the study of social insects has lagged behind in this regard is that the complex social environment of their colonies has a strong effect on social insect phenotypes and it is difficult to disentangle effects of genes from the effects of shared social environment. In fact, the social environment itself can have a genetic basis and can evolve because it is provided by nestmates. Most progress in elucidating the genetic basis of social insect phenotypes has been made by ignoring contributions of the social environment.

The purpose of this research project was to further develop and implement recently emerging evolutionary genetic approaches that formally consider genetic components of the social environment to study the complex genetic basis of social insect phenotypes. In order to this we developed a model genetic system, the pharaoh ant Monomorium pharaonis. Our major accomplishments were establishing a novel 'super-diverse' heterogeneous stock and completion of the first ever artificial selection study of a trait central to complex insect societies, caste ratio, defined as the proportion of individuals reared as reproductive queens versus sterile workers. This research provides novel insight into the genetic basis and evolution of complex social systems, and the evolution of complex societies, considered to be one of the major transitions in evolution on par with the evolution of multicellularity. Besides these empirical achievements, related evolutionary genetic theory was developed to provide insight into the genetic basis and evolution of complex social traits. This theory helps to explain why genetic variation for caste ratio, and other examples of 'social cheats' are maintained in social systems, how genetic variation for kin recognition and cooperation is maintained, and how social interactions influence the maintenance of genetic sequence variation.

Another important goal of the project was dissemination of knowledge to the host institution, the Centre for Social Evolution, University of Copenhagen, and the broader European community. I achieved this goal through training two PhD students, a Master's student, and seven undergraduates. Furthermore I organised the first ever PhD course on 'Evolutionary genetics of social evolution' that I taught alongside seven leaders of the field.

Overall, this research helps to develop novel approaches to study the complex genetic and evolutionary underpinnings of complex social systems. Furthermore, it helps to establish social insects as a model system to study the genetic basis and evolution of complex social systems.