I hope you will excuse me starting by talking about myself but it might help to explain some of my background and how I came to write this book. When I was doing my bachelor's degree in Zoology at the University of Bristol in England, one of my final year projects was on the structure of the eggshell, and the hatching mechanisms of the eggs, of a nematode parasite of cockroaches that rejoices in the splendid name of Hammerschmidtiella diesingi (named after a German nema-tologist, Hammerschmidt). Nematodes are a group of worm-like invertebrate animals. The eggshell turned out to have complex systems of pores and spaces in its outer layers. I stayed on at Bristol to do a PhD that followed up this work and looked at the eggshells of a variety of parasitic nematodes. The nematode eggshell is one of the most resistant of all biological structures. In some cases, it can even survive immersion in concentrated sulphuric acid. The eggshell has a layer of lipid, which restricts the exchange of materials between the egg and its environment. The eggs lose water very slowly when exposed to desiccation, enabling the larvae enclosed within them to survive the total loss of water from the egg. The pores in the eggshell of H. diesingi are involved in this process.

The free-living stages of some parasitic nematodes (those developing after the hatching of the egg), and of some free-living nematodes, show extraordinary abilities to survive extreme environmental stresses. They will tolerate freezing, complete desiccation and exposure to chemicals that are fatal to most other organisms (such as the fixatives used to kill and stabilise specimens for microscopy). Most of my career has been involved in trying to determine the mechanisms by which nematodes survive these extreme insults. I have gradually transformed from being a parasitologist (who studies the biology of parasites) into an environmental physiologist (who studies the interactions between organisms and their environment). When I moved to New Zealand in 1985, I had the opportunity to visit the Antarctic. The organisms that live in the rare terrestrial Antarctic sites that will support life are living in one of the most extreme environments on Earth. Experiencing such conditions myself stimulated my interest in extreme life even more.

Nematodes, of course, are not the only organisms that are able to survive in extreme environments. Since about the 1960s, we have become aware that a variety of microorganisms can flourish in all sorts of extreme conditions and that life is possible where it was previously thought to be impossible. This has broadened our understanding of the nature of life on Earth and the possibility of life elsewhere in the universe. In this book, I attempt to cover all types of organisms (animals, plants and microbes), the different types of extreme environments and the different aspects of their biology in these environments. I will also try to develop a framework for deciding what is extreme for life and for thinking about the biology of extreme organisms. This has been a large task - I will leave it to you to decide how well I have succeeded! Most people who have written about organisms in extreme environments are microbiologists or biochemists. As a zoologist, I am perhaps aware of a wider (or at least a different) range of organisms and approaches. I thus hope to bring a different perspective to the subject.

The book is written to be understandable by a non-expert (and hopefully even those with little background in biology or science). I have tried to explain things as I've gone along, but there is also a glossary to clarify unfamiliar terms. In order to keep the readability of the text, I have not formally cited references to original research papers. Instead, I have tried to include in the bibliography those that will enable the source of original research to be found and also mention in the text some of the major workers in the relevant areas. If any of my scientific colleagues feel that their work should have been directly cited, and was not, my apologies to them.

I would like to thank especially my wife Ann who, apart from supporting me during the writing of the book, read every chapter and, since she is not a scientist, helped me to make it more readable and understandable. Thanks also to my (now ex-) research student, Brent Sinclair, who also read every chapter and who was not shy about making suggestions for improvements. I would also like to thank those who read and commented on individual chapters and/or the book proposal: Carolyn Burns, Colin Townsend, Dev Nyogi, Bill Block, Don Gaff, Hans Ramlov, Craig Cary, Rick Lee and Graham Young. It was John Montgomery, of the University of Auckland, who started me thinking about resistance and capacity adaptations in relation to extreme environments. Jo Ogier has produced some wonderful illustrations and Ken Miller and Matthew Downes assisted me with those I prepared myself. Don Gaff and Craig Cary kindly supplied me with copies of their illustrations. The sources of material for illustrations, and relevant permissions, are acknowledged in the figure legends, where appropriate. Finally, I would like to thank my editors at Cambridge University Press, Alice Houston and Simon Mitton (and their team), for guiding me through the process of producing this book.

David A.Wharton Dunedin New Zealand

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