Mechanisms underlying responses to environmental stress in Drosophila

Organisms occupy ever-changing environments shaped by factors such as temperature fluctuations, resource availability, and social interactions, all of which exert profound effects on their chances of survival and reproductive success. Among these dynamic interactions, Drosophila melanogaster males exhibit a remarkable sensitivity to their social surroundings, leading to variations in lifespan, mating duration, and reproductive outcomes when they are kept in pairs as opposed to isolation. This thesis brings together the role of abiotic factors, the social environment and the mechanisms that underpin these processes to reveal the nuanced interactions that Drosophila has with its environments. I initially investigate the sensory perception of stress. Males utilise multiple cues to respond to the social environment in terms of mating duration, however the reduction of lifespan was found to not be linked to these sensory cues. I next aimed to understand how these same social environment responses were affected when exposed to environmental stressors; temperature, desiccation and circadian rhythm. While desiccation primarily affected mating propensity and elevated temperatures led to reduced lifespan and the elimination of rival responses, the mating duration phenotype proved remarkably resilient to mild stressors. Interestingly, while D. melanogaster demonstrates remarkable reproductive resilience to thermal fluctuations, closely related species exhibit varying degrees of sensitivity to temperature, with male fertility being particularly susceptible. Our examination of reproductive output and heat shock protein expression following exposure to mild thermal stress at 29°C revealed notable differences across species, with hsp70 showing a particularly pronounced response to thermal fluctuations in resilient species. Finally, I investigate the patterns of epigenetic inhibitors. Inhibitors of methyltransferases and histone deacetylases significantly altered lifespan and mating duration in high sperm competition environments. Exposure to inhibitors also influenced expression changes in some genes, though interestingly this was dominated by changes in isolated flies. While the study highlighted the role of the epigenome in behavioural plasticity, the relationship between histone modifications, gene expression, and behaviour remains intricate.