Cognitive mechanisms underlying responses to sperm competition in Drosophila melanogaster

In this thesis I use Drosophila melanogaster as a model organism to study the possible cognitive mechanisms controlling plastic behavioural responses to sperm competition. This plastic behaviour involves a male D. melanogaster responding to the presence of a rival male by increasing mating duration when housed with a female. I provide a general context to the work (Chapter 1) before examining my model in more temporal detail by investigating how the length of time males were exposed to a high sperm competition environment affected maintenance time of the plastic behaviour. I show that for males to accurately portray the sperm competition environment in their behaviour over a useful timescale they must possess accurate sensory systems. Without these, behaviour is still fully plastic, but change occurs at a slower speed than males with full sensory ability (Chapter 3). I then show that extended mating duration is controlled by a suite of well-known learning and memory genes highlighting the need for specific memory pathways to reflect ecological change (Chapter 4). However, those same genes do not change in their expression due to increased sperm competition, potentially pointing to some other mechanism of temporal change underlying the behavioural change (Chapter 5). Due to this reliance on learning and memory, I show that an increase in sperm competition can affect cognitive ability, and increase expression of synaptic genes over a longer time period (Chapter 6). Finally, I summarise my thesis findings and discuss how future research can build on the research presented to develop the field (Chapter 7). My research shows that learning and memory is paramount for males to react to changes in the sperm competition environment on a relevant timescale where behaviour and the environment have not become mismatched. In addition, I show that sperm competition pressures can cause an increase in male individual cognitive ability, posing the question of whether competition is one of the main drivers of non-mammalian cognitive ability.