Chronobiology: biological timekeeping

Abstract

bTime is nature’s way of making sure everything doesn’thappen at once.Q Unknown.The earth’s environment imposes recurrent daily,monthly, and annual changes. Whether these changesoccur in temperature, light–dark cycles, tidal rhythms, orthe changing of the seasons, one common aspect is theirpredictability. Organisms have evolved mechanisms bywhich to anticipate these changes to maximize survivaland improve fitness. Mechanisms enabling anticipation ofenvironmental changes occur throughout phylogeny. Allorganisms studied to date, from single-celled algae tohumans, have evolved complex biological timing mech-anisms. It has been posited that these biological time-keeping systems ensure that biochemical processes occurin their optimal temporal niche. Over time, as complexityof organisms increased, biological timing mechanismsgrew to govern everything from vegetative physiologicalprocesses, to control of complex behaviors. A textbookwhich aims to discuss the field of chronobiology as awhole is faced with the mammoth task of explainingbiological timekeeping, from the simplest prokaryote tothe most complex eukaryote. In addition, such a bookmust tackle a wide range of issues, from a host ofdifferent fields running the gamut from moleculargenetics and cell biology, through to ecology, psychology,and even engineering. bChronobiology: Biological Time-keeping,Q edited by J.C. Dunlap, J.J. Loros, and P.J.DeCoursey [1], takes up this challenge.Chronobiology moves through the different levels ofanalysis used to dissect timekeeping mechanisms, progress-ing from the earliest behavioral observations, to moderngenetic, biochemical, and molecular techniques, which haveopened up new avenues of inquiry. This provides aframework for understanding the progression of knowledgein a field which draws upon diverse research areas, andunderscores today’s interdisciplinary approaches.The opening chapters of the text introduce the reader tothe historical background of timekeeping, from the firsttimekeeping mechanisms built by people, to the discoveryof the endogenous nature of biological clocks in plants andanimals. Next is a discussion on the evolutionary trendswhich are observed in nature. This highlights the generalityof biological clocks in simple and complex organisms. Forexample (page 12), Hastings and Sweeny discovered thatthe single-celled organism Gonyaulax (a dinoflagellate) hasa circadian rhythm in bioluminescence. They also firstdescribed the phase dependency of shifting the clock bylight. These studies showed that all of the importantproperties of a circadian clock could be found within asingle cell. The introductory chapters do an excellent job inpresenting the reader with a digest of the large literature onthe evolutionary history of biological timing in a mannerwhich is easy to understand, without sacrificing scientificrigor. A dense Chapter 3 discusses the fundamental proper-ties of circadian rhythms, from entrainment (i.e. synchroni-zation) to the external environment in the wild and thelaboratory, to mathematical modeling of circadian pace-makers. Some of the discussions of the different models ofpacemaker function are particularly challenging. Thesummaries and study questions at the end of this chapterare somewhat terse, especially compared to other chapters.Students would have found additional summaries and studyquestions helpful.Chapter 4 reviews research on circannual rhythms andphotoperiodism. This chapter provides a student new to thisarea of research with a background on the variety of