Summary: Kronfeld-Schor et al. (2013)

The circadian "clock" is the body's internal mechanism for keeping track of time. This "clock" is driven by an individual's physiology and it influences an animal's behaviour on a daily basis. Alterations to environmental light conditions results in the natural time-keeping rhythms to become entrained to particular light-dark (day-night) cycles. The circadian system consists of molecular, cellular, tissue and organismal levels, and how these levels contribute to an individuals behaviour is quite well understood. The shortcomings of these studies relate to the species studied, typically those that are standard laboratory species that have been maintained in captivity (so called "model" organisms). Kronfeld-Schor et al. (2013) suggest that to understand the evolutionary significance of the circadian clock, we need to study a variety of species from multiple taxonomic groups that display a diversity in activity patterns (e.g. diurnal, nocturnal, cathemeral, crepuscular). In a special feature of the Proceedings of the Royal Society of London B, Kronfeld-Schor et al. (2013) highlight seven papers that attempt to explore the adaptive significance of the circadian clock, with the reviews including the influence of moonlight, latitude, evolutionary history, sociality, temporal niche specialization, annual variation and post-transcriptional mechanisms. These seven papers demonstrate the complexity, as well as the diversity, of the circadian system.