Male stalk-eyed flies have highly exaggerated eyespan. This is a classic example of sexual selection, caused by strong female mate preferences for males with wider eyespan. We know this trait imposes aerodynamic costs on males (they take-off at a lower angle, due to the extra head weight), it slows development (males take 1-2 extra days to emerge from pupae) and is a highly condition-dependent trait (being very sensitive to environmental and genetic stress). Eyespan is a means for females to assess male phenotypic and genetic quality. The project will break new ground in examining the energetic costs of exaggeration. The student will measure a range of metabolic parameters in males, e.g. oxygen consumption and reactive oxygen species (ROS) flux. By introducing different substrates, the performance of mitochondrial complexes I-IV can be assessed under environmental stress. These features of the energetic state will be compared across males with different eyespan exaggeration. The student will compare different tissues (head, thorax and reproductive organs) in males and females, as well in larvae when eyespan size is determined. Transcriptomic analysis will also be undertaken to understand how gene expression feeds into phenotype. We hypothesize that metabolic trade-offs between investment in growth and development versus aerobic capacity for flight and aerodynamics underpin differences in eyespan, with the honesty of the handicap signal primarily reflecting metabolic fitness.