Photoperiodism. The biological calendar

Abstract

Photoperiodism –the biological calendar is a welcome contribution to the field of photoperiodic research because it brings together and summarises current understanding of the photoperiodic mechanisms present in all organisms, from animals and plants to invertebrates and fungi – something that has been needed for a long time. The book is appropriately divided into three sections, the first dealing with photoperiodism in plants and fungi, the second with photoperiodism in invertebrates, and the third with photoperiodism in vertebrates; at the start of each there is an overview written by one of the editors who are well known in those areas. Each section contains chapters written by researchers who are specialists on that particular topic. For example, the first section on plants and fungi starts of with a chapter on the photoperiodic flowering in arabidopsis written by Putterill et al., which covers the historical perspective describing the discovery of photoperiodism, the development of various models to explain the observed circadian phenomena, and the current knowledge of the molecular pathways controlling photoperiodic flowering in this long-day plant. This sets up nicely a comparison with the photoperiodic mechanisms in the short-day plants rice and Pharbitis covered in the following two chapters written by Izawa and Hayama, respectively. Dormancy in trees, another aspect of plant development also controlled by photoperiod, is described in one of the chapters, although it is a pity that other photoperiodic responses in plants, eg. tuberization, are not covered. The molecular basis of the important interaction between daylength and temperature in determining seasonal plant responses is described by Michaels, and seasonality in fungi is covered in the final chapter. Section two covers photoperiodic responses in invertebrates: whilst there are chapters on snails and copepods, the focus is mainly on photoperiodic responses in insects. This includes an inter-related set of chapters by Saunders on insect migration, e.g. that of the monarch butterfly, and also diapause, which is essential for survival of the cold temperatures of winter, by Goto et al. on circadian clock genes in insects, and by Williams et al. on the molecular role of some of these genes in the control of diapause. The last two chapters of this section by Nijhout and by Hardie deal with the effect of photoperiod on insect morphology, such as seasonal effects on butterfly wing patterns/colouration and on the development of winged or wingless forms of aphid. Photoperiodic responses in a wide range of vertebrates (fish, reptiles, birds and mammals) are covered in the final section. The differences in the photoperiodic response mechanisms between different vertebrates are discussed, such as the importance of temperature in the seasonal responses of amphibians and reptiles, and the differing importance of melatonin in regulating the response to photoperiod. The emerging role of thyroid hormones in regulating the photoperiodic response in birds and mammals is covered in chapters by Yoshimura and Sharp, and Hazlerigg, respectively. This section on vertebrates focuses mainly on seasonal reproduction, but it also contains a chapter on the effect of photoperiod on non-reproductive traits such as the immune system and behaviour by Demas et al., and migration in fishes is also discussed in a chapter by Borg. Having different chapters on similar topics written by different authors always runs the risk of a certain amount of repetition, and this is certainly the case in some chapters of this book, although it is not too much to be off-putting. There is a certain level of assumed knowledge from some of the authors in some of the chapters, and so this book is not well suited for the complete novice but is targeted more at readers with some familiarity of this field of research who would like to expand their knowledge of photoperiodic mechanisms in different organisms. In short this book provides a pretty comprehensive summary of the current understanding of photoperiodic responses in a wide range of organisms.