Daily rhythms on zooxanthellate and azooxanthellate corals, an integrative approach of gene expression, microbiome, physiology, and environmental parameters

Abstract

Environmental rhythms regulate the behavior and physiology of all living organisms. The most conspicuous rhythm is the light:dark cycle, regulating metabolic states, physiologic process, reproduction, and behavioral activities either by an endogenous circadian clock or as a simple response to light. The circadian clock mechanism as well as gene expression profiles are widely known for model organisms, but it has been explored for cnidarians only in the last few decades. Scleractinian corals are known to have the same core circadian genes observed in mouse and fly, suggesting that the ability to perceive, anticipate, and respond to constant changes in the environment arose early in animal evolution. Interestingly, some of the core circadian genes seem to behave differently in corals, losing rhythmicity under constant darkness. Furthermore, the symbiotic relationship with dinoflagellate algae from the family Symbiodiniaceae complicate studies, and most of the available results on circadian gene expression patterns are performed for the holobiont. Here we propose an unprecedented approach, in which the symbiont is isolated from the coral tissue after collection for an independent evaluation of the gene expression, microbiome, and physiological parameters of both parts in symbiosis, correlating them with environmental variables. The results will serve as a baseline about the functioning of healthy corals and how the host coral and its symbionts respond to the light:dark cycle. In this context, Madracis decactis, a zooxanthellate species, and Tubastraea coccinea, an azooxanthellate species will be studied and will compose the first study in the South Atlantic on the circadian clock in an integrative and transdisciplinary way. (AU)