Seasons of life : the biological rhythms that enable living things to thrive and survive PDF
Preview Seasons of life : the biological rhythms that enable living things to thrive and survive
SEASONS OF LIFE ‘Much has been written about the circadian clock. Foster and Kreitzman focus on the less familiar circannual clock, which governs responses to seasonal changes and tells animals when to mate, migrate or hibernate – and plants when to grow and shed leaves. A complicated story but a joy to read.’ Financial Times ‘Seasons of Life is … compelling. Beneath the litany of statistics and scientific evidence there is a profound awe of the subtle rhythms and invisible mechanisms of the natural world, knowledge that may prove vital in the coming years.’ P. D. Smith, Guardian ‘Readable and enlightening … as the world has turned over millions of years, plants and animals have adapted to seasonal change and weather patterns. This might sound technical but in these authors hands, turns out to be deeply compelling.’ Jonathon Wright, Herald (Glasgow) ‘This tour-de-force addresses everything from feedback regulation of clock proteins to how migrating animals who navigate by the sun compensate for its apparent daily motion. The chapter on seasonal affective disorder helps explain our own winter trips. Elegant prose and clear diagrams make even the most complex physiology comprehensible. A must read for anyone who has ever looked up at a migrating skein of geese and wondered “how do they know …?”’ Adrian Barnett, New Scientist USA RUSSELL FOSTER FRS is a Professor of Circadian Neuroscience, Chair of the Nuffield Laboratory of Ophthalmology and a Senior Kurti Fellow at Brasenose College at the University of Oxford. LEON KREITZMAN is a scientific writer and broadcaster, a widely respected futurologist and author of The 24 Hour Society. The authors also co-wrote Rhythms of Life which describes the rhythms of the daily cycle and was translated into five languages. ALSO BY RUSSELL G. FOSTER AND LEON KREITZMAN Rhythms of Life SEASONS OF LIFE The biological rhythms that enable living things to thrive and survive Russell G. Foster & Leon Kreitzman Dedicated to the memory of Professor Eberhard (Ebo) Gwinner 1938–2004 Founding director Max-Planck-Institut für Ornithologie ‘He was not only one of the most influential ornithological researchers of the second half of the twentieth century, but also a remarkable friend, colleague and mentor’ (Brandstaetter & Krebs, 2004). CONTENTS Foreword Acknowledgements Introduction 1 The generation of the seasons 2 Adapting to seasonal change 3 Anticipating seasonal change in plants 4 Seasonal reproduction in mammals and birds 5 Staying put in the cold: hibernation and diapause 6 Timing migration 7 Seasons and human evolution 8 Timing reproduction in humans 9 Birth month effects 10 Disease and seasonal timing 11 Seasonal affective disorder 12 The seasonality of dying 13 We are all phenology freaks now Glossary of common terms Appendix I References Index FOREWORD In their first book on biological time, entitled Rhythms of Life, Russell Foster and Leon Kreitzman told how cells measure the time of day with what is called a circadian clock. That truly remarkable clock has a periodicity of 24 hours and shows all the hallmarks of a watch devised by us humans. Each day the ‘pips’ make sure that it keeps precisely in tune with the rotation of the earth and it is temperature compensated. Its role is to ensure that the myriad events of life occur in sequence each day. In this volume – Seasons of Life – they take us on to the story of how life adapts to changes of season. Those changes are dramatic indeed at the poles, and it is obvious that without great alterations life in these extreme regions would be impossible. That applies to a slightly lesser extent in the temperate zones but it is still critical to survive cold winters and hot summers, and to produce young at just that season of the year for them to survive to maturity. It comes as no especial surprise, therefore, that animals and plants not only have a daily clock but also possess a calendar that tells the organisms what time of year it is. We understand much about the calendars involved but not yet enough. As this book shows, there are (at least) two sorts of calendar. One is based on circadian clocks and allows the organism to work out daylength, which is a sound proxy for time of year. If that is not remarkable enough, then the other way of measuring time surely is! Many organisms seem to possess a clock with an innate periodicity of about one year and, by analogy with the daily clock, it is called a circannual clock. How it is constructed is unknown but for animals that hibernate or spend their winters in the deep tropical forests away from changes in daylength, it offers a precise calendar. That may be how organisms time the year, but this is where seasonality really starts to become intriguing. Virtually every process is best carried out at one time or other of the year and that is not something to take lightly. Survival depends on it, and transmitting one’s genes into the next generation certainly does. Much of this book is devoted to the wonderful processes that occur seasonally. The most obvious examples are the migration of birds and large mammals to avoid unpleasant winters and yet who return with unerring accuracy the following year. The alternative strategy is to avoid inclement winters altogether by hibernation in rodents, diapause in insects, dormancy in plants. Finally one has to breed at that time when the young stand the best chance of themselves surviving to maturity. This is invariably determined by chance of themselves surviving to maturity. This is invariably determined by the availability of food for the newly born offspring, and so the seasonal cycles of many species become inextricably connected. This is where climate change is intruding into this carefully evolved system. Earlier springs cause caterpillar emergence to advance in Wytham Woods near Oxford, and so the great tits had better track these changes and advance the date of egg-laying or they will become extinct. There is much more to seasonality, though, than breeding or migration. Virtually every internal process alters. Male red deer restrict food consumption quite drastically during Alpine winters as part of their survival strategy, even though, of course, they do not hibernate. This does not happen because food is absent, although one might imagine so. Take the deer down to lower altitudes and still it eats less. We humans were clearly highly seasonal beasts until the coming of electric light but traces remain. So-called seasonal affective disorder (SAD) is an example, although as in so many stories one has to disentangle fact from supposition. Foster and Kreitzman attempt this and many other challenges in what is a wonderful story. Sir Brian Follett FRS, Department of Zoology, University of Oxford ACKNOWLEDGEMENTS Several summers and autumns – and winters and springs for that matter – have passed since we first thought of writing this book. We tried the patience of family, friends and publishers but we managed to finish, with no small thanks to academic colleagues who reviewed our work with a critical eye. Barbara Helm, Stuart Peirson, Jim Hardie, David Saunders and Daniel Rock read through the entire draft, and their helpful comments on the overall structure and content has been of enormous benefit, as has the particular expertise they brought to various chapters. Harriet McWatters kindly read Chapter 3 and gave us the benefit of her friendly criticism and comment; a very big thank you is due to Barbara Helm, who also advised on Chapters 4, 5, 6 in detail; Andrew Loudon and David Hazelrigg provided expert help on Chapter 4; Bambos Kyriacou reviewed Chapter 5; Till Roenneberg was extremely helpful with Chapters 8 and 9, and Daniel Rock provided valuable comments and material for Chapter 12. Ben Lobley and Sally Pellow read the entire draft for style and coherence, and the late Mike Karger assisted on early drafts. Philippe Rousseau kindly helped with our references to ‘classical’ writings. We would also like to thank the referees who read through the first version of the final manuscript at the request of the publishers. They will recognise their anonymous but vital help in the comments and critiques incorporated into the final text. Any errors are solely down to us, and the last people to whom they can be attributed are Andrew Franklin of Profile Books & Serpents Tail, and Jean Black of Yale University Press. We are fortunate in having had guidance from such distinguished and wise editors. Helga Gwinner graciously put us in touch with colleagues who had worked with her late husband, and also provided us with relevant papers and books. Our thanks go to colleagues at The Nuffield Laboratory of Ophthalmology and Brasenose College, University of Oxford, for their sustained enthusiasm and support for this project. This is the second book we have written together, and familiarity has its ups and downs. That we managed without too much friction is due in no small part to the support of our families. Thanks are due again from L.K. to Linda, Sophie to the support of our families. Thanks are due again from L.K. to Linda, Sophie and Leah, and from R.G.F. to Elizabeth, Charlotte, William and Victoria. Both of us know how boring it can be for the rest of the family when the writer retreats to ‘the book’, and we are grateful for the forbearances we have been shown.
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