Seasonal cycles select for self-sustained circadian oscillators.

Area of Science:

• Chronobiology
• Evolutionary Biology
• Genetics

Background:

• Circadian clocks are widespread timekeeping mechanisms crucial for anticipating daily environmental changes, providing a fitness advantage.
• A key feature of circadian clocks is their ability to maintain self-sustained oscillations, even in constant environmental conditions.
• The evolutionary advantage of self-sustained oscillations in circadian systems, despite evolving in variable environments, remains a key question.

Purpose of the Study:

• To investigate the environmental pressures that select for self-sustained circadian oscillators.
• To determine if seasonal photoperiod changes are sufficient to drive the evolution of self-sustained circadian clocks.

Main Methods:

• Utilized an experimental analysis involving competition among strains with differing phenotypes.
• Focused on the impact of changing photoperiods, simulating seasonal variations.
• Compared experimental findings with previous extensive modeling analyses.

Main Results:

• Experimental analysis revealed that changing photoperiods are a sufficient environmental pressure for selecting self-sustained circadian oscillators.
• This selection occurs even in the absence of fluctuations in other environmental factors like temperature.
• Findings contrast with modeling studies suggesting combined weather and daylength variability are necessary.

Conclusions:

• The evolution of self-sustained circadian clocks is significantly shaped by environmental cycles of multiple periodicities, including daily and seasonal variations.
• Seasonal photoperiod modulation is a critical selective pressure driving the ubiquity of self-sustained circadian oscillators.
• Circadian clock properties are molded by the interplay of daily and annual environmental cycles.