Mating imperatives drive plasticity of the daily temporal niche in fruit flies.

Animals confine their daily activity to distinct diurnal, crepuscular or nocturnal windows. It remains unclear how hundreds of sympatric species sharing the same temporal niche manage to coexist. To address this, we monitored the daily activity of the twilight-active, species-rich Drosophila genus under naturalistic conditions. Here we show that intense sociosexual interactions rapidly drive a species-specific reformatting of their canonical crepuscular niche. The dominant sensory modality used for sexual communication predicts niche-shift direction: reliance on chemosensation for courtship redirects behavioural activity into the night, while visual reliance shifts it into the day. This temporal plasticity bypasses the circadian clock, instead operating via a conserved dopaminergic pathway that simultaneously inhibits sleep and sustains sexual motivation. Our results reveal how mating imperatives enable conditional colonization of otherwise restricted temporal windows. Ultimately, by driving the divergence of previously overlapping niches, sociosexually induced temporal plasticity provides a powerful mechanism for sympatric coexistence in crowded environments.