| The study of the social environment of Drosophila melanogaster has revealed social effects on the regulation of genes, physiology, and behaviour. More recent studies have also uncovered complex, group-level phenotypes that defy explanation through a dyadic framework of interactions. Yet studies characterizing the group's internal dynamics---organisation and synchronisation---are sorely lacking. I address this by implementing a new methodological paradigm to study Drosophila melanogaster groups. My initial contribution establishes a robust new phenotype---Social Interaction Networks---that quantifies the structure of a given set of interactions within a group. Prior to this, Drosophila were sometimes thought of as solitary agents which, lacking a suitable courtship or aggressive target, would aimlessly move about randomly encountering other individuals. I show that these 'random encounters' in an arena are in fact non-random, and that their organisational structure varies among strains and sex. Secondly, I use a novel rule-set to automatically determine and characterize these non-random 'encounters', and to show their dependence on chemosensory feedback. By determining and standardizing the ways in which flies interact, I show an increased power in the ability to explore the Social Interaction Networks of flies.;Finally, I measure the effect that group size has on the Social Interaction Networks of Drosophila, and examine the flies' ability to compensate for density effects by adjusting their interactive behaviours within the group. I also test the effect that group size has on group identity, by examining in tandem both behaviour and genetic regulation, to reveal a synchronising effect in a group of freely interacting flies. I find a complex sex-dependent relationship between group size and synchrony, although both males and females benefit from larger group sizes.;This thesis therefore reports novel methods and findings that take us closer to understanding the complex social life that patterns itself inside Drosophila melanogaster groups. |
