Abstract
Life on earth adapted to the daily reoccurring changes in environment by evolving an endogenous circadian clock. Although the circadian clock has a crucial impact on survival and behavior of solitary bees, many aspects of solitary bee clock mechanisms remain unknown. Our study is the first to show that the circadian clock governs emergence in Osmia bicornis, a bee species which overwinters as adult inside its cocoon. Therefore, its eclosion from the pupal case is separated by an interjacent diapause from its emergence in spring. We show that this bee species synchronizes its emergence to the morning. The daily rhythms of emergence are triggered by temperature cycles but not by light cycles. In contrast to this, the bee’s daily rhythms in locomotion are synchronized by light cycles. Thus, we show that the circadian clock of O. bicornis is set by either temperature or light, depending on what activity is timed. Light is a valuable cue for setting the circadian clock when bees have left the nest. However, for pre-emerged bees, temperature is the most important cue, which may represent an evolutionary adaptation of the circadian system to the cavity-nesting life style of O. bicornis.
Highlights
We find evidence for circadian clocks everywhere in nature, many aspects of the underlying clock mechanisms, and the behaviors that result from them, are yet to be understood
We focused on the spring bee Osmia bicornis (“red mason bee”), which provides the possibility to study the timing of emergence which is dissociated from eclosion
Under temperature cycles bee emergence was tightly regulated by the Zeitgeber temperature, as most bees emerged within a 2 hour time frame every day, www.nature.com/scientificreports whereas under light-dark (LD) cycles bees emerged with no clear rhythmicity
Summary
We find evidence for circadian clocks everywhere in nature, many aspects of the underlying clock mechanisms, and the behaviors that result from them, are yet to be understood. The raw data of the emergence events across 13 days, plotted with a time bin of 2 hours (Fig. 1A), demonstrate that under constant conditions (treatment DD) following synchronization with temperature cycles bees emerged with a daily rhythm.
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