Current Understanding of the Circadian Clock Within Cnidaria

Molecularly-based timing systems drive many periodic biological processes in both animals and plants. In cnidarians these periodic processes include daily cycles in metabolism, growth, and tentacle and body wall movements and monthly or yearly reproductive activity. In this chapter we review the current understanding of biological clocks in the cnidaria, with an emphasis on the molecular underpinnings of these processes. The genes that form this molecular clock and drive biological rhythms in well-characterized genetic systems such as Drosophila and mouse are highly conserved in cnidarians and, like these model systems, display diel cycles in transcription levels. In addition to describing the clock genes, we also review potential entraining systems and discuss the broader implications of biological clocks in cnidarian biology.