The effect of temperature compensation on the circadian rhythmicity of photosynthesis in Symbiodinium, coral-symbiotic alga

Circadian rhythms, which are found in most eukaryotes, are defined as rhythms that persist under constant conditions with a periodicity close to 24 h. One central key characteristic of all circadian rhythms is "temperature compensation", which allows organisms to maintain robust rhythms with a period close to a diel cycle over a broad range of physiological temperatures. To better understand the response of the circadian clock in corals to temperature elevation, photosynthesis as an output process of the circadian clock was studied both in Stylophora pistillata corals and in cultured Symbiodinium algae. The time period of photosynthesis was not affected by temperature elevation in the cultured algae or in the corals harbouring Symbiodinium. However, the photosynthetic system responded to temperature elevations by adjusting the photosynthetic apparatus. These findings suggest that the endogenous algal circadian clock regulates the photosynthetic rhythm and compensates for temperature elevations that occur in the natural environment.