Behavioural correlates of chronic stressors in outbred and dispersal selected Drosophila melanogaster

Abstract

When faced with a stressful situation, an organism exhibits a behavioural stress response. Studying these responses can allow us to model and understand stress induced disorders, such as depression and anxiety, in humans better. This study examines behavioural changes due to stress in Drosophila melanogaster, focussing on how sex and selection for increased dispersal can modulate this response. The behaviours studied, namely, anhedonia, motivation to explore and disperse, locomotor activity and sleep levels, have been well-investigated in human and rodent-based models of stress-disorders. These behaviours were studied in the context of two different stressors, namely mechanical perturbation and adult crowding. While mechanical perturbation caused anhedonia and made flies restless across sexes, the changes in these behaviours was sex-dependent after adult crowding. Further, evolutionary history of increased dispersal changed how flies responded to stress, with females selected for dispersal being highly resistant to stress as compared to controls. Changes in locomotor activity and rest levels after stress in the selected populations was crucially dependent on the presence or absence of food while recording and post-stress rest before recording. This study thus argues for a sexually dimorphic model of stress in the fruit fly, which can provide better appreciation of the sexual dimorphism in stress-induced mood disorders in humans. Additionally, it establishes that the environment of evolution can modulate stress-responses, furthering the argument for stress-induced disorders in humans to be due an evolutionary mismatch. This also paves the way for studies on how other evolutionary histories can shape this response.