FIGURE 2.

Diagram showing the results of experiments done previously to test the adaptive value of the circadian clock in cyanobacteria (first and second row), as well as a proposed experiment (third row). Experiments in the first row refer to publications described in the text (Ouyang et al., 1998; Woelfle et al., 2004; Ma et al., 2013), and show that resonance between the circadian period (FRP = free-running period) and the environmental period increases cyanobacterial fitness, while no difference was observed in constant conditions (LL). Experiments in the second row are explained in more detail in the text (Woelfle et al., 2004; Ma et al., 2013), and show that cyanobacteria with circadian clocks outcompete clock-less cyanobacteria in rhythmic (LD) but not in constant (LL) conditions. This latter result was unexpected given the typical bias among chronobiologists that circadian clocks would be able to increase fitness by facilitating proper internal temporal order. The last row features an experiment that is yet to be reported, namely, interspecific competitions between different species of cyanobacteria. A possible prediction of this experiment is that the co-existence or not of the two species would be modulated by the environmental rhythmic conditions, and perhaps by the two species’ circadian clocks.