We all modify our behaviour in different social situations to adapt, fit in or to become more competitive. Fruit flies also have complex social lives, aggregating independently of any resources, engaging in social learning, forming social networks and having a genetic propensity for different types of social environments. Using Drosophila melanogaster fruit flies as a model, we can investigate both the fitness consequences of changes of social environment and the mechanisms by which individuals can respond to such changes.
One aspect of the social environment that has a particular impact on males is how much mating competition (both before and after mating) they encounter. Theory predicts that if males can mate more than once they need to trade-off current and future mating opportunities, hence they should modify their mating effort at a particular mating depending on the amount of competition they face. Males of many species use plastic strategies to cope with this uncertainty, taking cues from the presence of other males or the mating status of females, and making adjustments to behaviour and ejaculate content accordingly. In D. melanogaster, after being exposed to a potential competitor, males mate for longer and transfer a higher quality ejaculate. This has fitness benefits, at least in the short term, but is costly. By combining behavioural and life history data with transgenics and transcriptomics, we can investigate how such responses are coordinated and regulated, an important step in understanding how sophisticated, flexible social behaviours evolve. We are also starting to use this paradigm to investigate other consequences of social contact on traits such as ageing, immunity and cognition.