摘要：SummarySolar light/dark cycles and seasonal photoperiods underpin daily and annual rhythms of life on Earth. Yet, the Arctic is characterized by several months of permanent illumination (“midnight sun”). To determine the persistence of 24h rhythms during the midnight sun, we investigated transcriptomic dynamics in the copepodCalanus finmarchicusduring the summer solstice period in the Arctic, with the lowest diel oscillation and the highest altitude of the sun's position. Here we reveal that in these extreme photic conditions, a widely rhythmic daily transcriptome exists, showing that very weak solar cues are sufficient to entrain organisms. Furthermore, at extremely high latitudes and under sea-ice, gene oscillations become re-organized to include <24h rhythms. Environmental synchronization may therefore be modulated to include non-photic signals (i.e. tidal cycles). The ability of zooplankton to be synchronized by extremely weak diel and potentially tidal cycles, may confer an adaptive temporal reorganization of biological processes at high latitudes.Graphical AbstractDisplay OmittedHighlights•Transcriptomic rhythms persist inC. finmarchicusduring the midnight sun period•Daily transcripts dominate in ice-free environments and at lower latitude•Ultradian transcripts are revealed under sea-ice and at higher latitude•Reorganization of the transcriptome might be an adaptation to under-ice tidal cuesMicrobiology; Systems Biology; Transcriptomics
