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.
