A cellular basis for the mammalian nocturnal-diurnal switch
Summary
Early mammals were nocturnal while dinosaurs dominated the daytime. Mammalian transition to daytime activity accelerated after the Cretaceous-Paleogene extinction, but the underlying mechanisms remain unclear. We identified a conserved cell-intrinsic, thermodynamic mechanism that likely facilitated this shift. In cells from diurnal mammals, protein synthesis, phosphorylation, and circadian timing were less sensitive to temperature changes than were cells from nocturnal mammals. Comparative
Content
# A cellular basis for the mammalian nocturnal-diurnal switch
*Published: 2026 Feb 26*
Early mammals were nocturnal while dinosaurs dominated the daytime. Mammalian
transition to daytime activity accelerated after the Cretaceous-Paleogene
extinction, but the underlying mechanisms remain unclear. We identified a
conserved cell-intrinsic, thermodynamic mechanism that likely facilitated this
shift. In cells from diurnal mammals, protein synthesis, phosphorylation, and
circadian timing were less sensitive to temperature changes than were cells from
nocturnal mammals. Comparative genomics revealed accelerated evolution within
essential signaling pathways, including mechanistic target of rapamycin (mTOR),
that increase the robustness of diurnal cellular clocks to thermal and osmotic
perturbation. In nocturnal mice, mTOR inhibition shifted cells, tissues, and
behavior toward diurnal activity. These findings uncover a genetic and
biochemical basis for nocturnal-diurnal switching, emphasizing how cellular
signaling networks can encode complex phenotypes such as temporal niche
selection.
DOI: 10.1126/science.ady2822