Widely rhythmic transcriptome in Calanus finmarchicus during the high Arctic summer solstice period.

Laura Payton,Elizaveta Ershova,Lukas Hüppe,Céline Noirot,David Wilcockson,Kim S Last,Claire Hoede,Bettina Meyer,Sophie Valière

doi:10.1016/j.isci.2020.101927

Abstract

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 copepod Calanus finmarchicus during 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.

Highlights

The day/night cycle structures biological processes from gene expression to physiology and behavior (Helm et al, 2017; Mermet et al, 2017)
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 copepod Calanus finmarchicus during the summer solstice period in the Arctic, with the lowest diel oscillation and the highest altitude of the sun’s position

Summary

Introduction

The day/night cycle structures biological processes from gene expression to physiology and behavior (Helm et al, 2017; Mermet et al, 2017). Organisms may respond directly to external stimuli (exogenous) or indirectly (endogenous) via the internal circadian clock This molecular mechanism enables organisms to track changes in their environment by using the highly predictable light/dark cycle as a Zeitgeber (time-giver) other clocks are known to synchronize to other monotonous cycles (i.e. tidal, lunar, and annual). Endogenous clocks are of adaptive advantage because they enable organisms to anticipate and prepare for predictable environmental changes by temporally organizing short- and long-term biological processes (Helm et al, 2017). It is still unclear how this temporal biological organization is facilitated in organisms inhabiting extreme photic environments. The persistence of daily rhythms is questionable during the summer solstice, which represents the paroxysmal period of midnight sun, with the lowest diel oscillation and the highest altitude of the sun’s position above the horizon (Schmal et al, 2020)

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Conclusion