Socio-sexual cues shape female diet choice in Drosophila melanogaster

Male harassment can disturb female feeding behaviour and limit females’ access to preferred foraging locations. However, it is not yet known how females trade off costs of sexual harassment or increased intrasexual competition against preference for dietary macronutrients when making foraging decisions. We used the fruit fly Drosophila melanogaster to investigate how female foraging decisions were affected by cues of conspecific presence and interactions with males. We assessed the strength of female choice for high-protein versus low-protein diet patches for foraging and oviposition in either single-sex groups, during direct interactions with males, or when exposed to cues of males or females (‘restricted’ conspecifics held within a transparent barrier, allowing auditory, visual and chemical cues but preventing physical contact and direct disturbance). Contrary to predictions, females did not avoid foraging or laying eggs on patches that had cues of male presence. Instead, females prioritised associating with restricted males, overriding harassment risk and diet preferences. In a subsequent experiment, we found that females were attracted to cues of conspecifics of either sex, even when those cues were derived from low-protein food patches. Female attraction to food patches with cues of conspecifics, for both feeding and reproduction, suggests that cues from socio-sexual partners are used in foraging decisions and can modulate, or sometimes override, diet quality preferences.