Insects' strategies for survival


Chown, S.L. & Nicolson, S.W. (2004) Insect physiological ecology — mechanisms and patterns. Oxford University Press, Oxford, UK. ix +243 pp., figs, tables, line diagrams, index. Hardback: price £70.00, ISBN 0-19-851548-0. Paperback: price £32.50, ISBN 0-19-851549-9.

The beginning of the 21st century has seen a revival of major publications in insect physiology: Klowden's Physiological systems in insects (2002), Nation's Insect physiology and biochemistry (2002), and now Chown and Nicolson's Insect physiological ecology. The first two take a more classical approach where physiological processes are discussed from an anatomical and biochemical perspective, and are thereby quite comprehensive, even though neither matches Wigglesworth's unique text, The principles of insect physiology (first published in 1939), which has dominated the 20th century. Because of the size of the class Insecta, only a multi-authored publication can do justice to, or provide an adequate analysis of the physiology of insects as influenced by the environment. The current contribution by Chown and Nicolson is a step in the right direction, essentially focused on ‘the ways in which insects respond to different components of the external environment’ (p. 177).

The book, written in a straightforward and readable style, provides a very concise account (out of 243 pages there are 111 figures — 10 of which occupy full pages — 3 tables and 45 pages of references) of four aspects of the insects’ strategy for survival: nutrition, metabolism and respiration, water balance, and temperature adaptation. It takes a cohesive look at the way in which insects exploit food resources, deal with gaseous exchange, survive with or without water and respond to temperature changes. Only two figures and one table make an original contribution to the field, the rest having been taken from publications in leading journals. The information presented is logically organized.

The 13-page introduction briefly discusses physiological variation, macrophysiology and the need to take a more integrated approach in physiological investigations, before presenting the objectives of the book and a rapid review of the various chapters. The figures appearing in this section could have been put to better use in the appropriate following chapters.

The authors use the last paragraph of the introduction to warn readers about what they do not cover in the book and ‘urge disappointed readers’ to seek information elsewhere ‘and then come back to this book’ (p. 13). Such a comment is unusual and normally directed at graduate students rather than the larger scientific community. Since this book does not dwell on hormonal regulation, muscle physiology, neuronal functioning, sensory perception, sclerotization, the physics of flight, insect clocks and diapause — all important dimensions of necessary physiological adaptations to the ever-changing environment — we have here a rather fragmented review of insect physiological ecology.

The major shortcoming of the introduction is the missed opportunity for an in-depth discussion of the differences between physiological ecology, environmental physiology (an expression used elsewhere in the text) and eco-physiology, terms which are in need of proper redefinition because they tend to be used interchangeably in the literature. After all, this is the first monograph on insect physiological ecology. Basically the authors can justify using ‘physiological ecology’ because they ‘examine interactions between insects and their environments from a physiological perspective’ (p. 10). The adaptations of insects to the ecosystems where they thrive are not discussed at the molecular level.

The book's subtitle is mechanisms and patterns. In this respect Chown and Nicolson have made a notable contribution to our understanding of insect physiology as influenced by environmental factors. They are to be commended for the space devoted to methods and measurement of physiological processes, mathematical analysis of these processes and their discussion and illustration of phylogenetic aspects of environmental adaptations.

Inevitably, by focusing on only four elements of adaptations to the milieux in which hexapods operate, and by extensive use of figures and tables from the reviewed literature, the authors have missed or neglected some important aspects. For instance, Chapter 2 (on nutritional physiology and ecology) is primarily devoted to physiology — and without the appropriate biochemical dimension — and does not dwell much on ecology. Only four pages are devoted to secondary plant compounds and their significance in insect nutrition and behaviour. Chemical ecologists will certainly be disappointed. It would have been appropriate to address plant–insect interactions in a context of global warming as insects extend their range, access new plant food sources, wild or cultivated, and adjust to more acute temperature/humidity fluctuations.

The authors’ admission that the subject matter presented in chapters 2 to 6 ‘has been dealt with in relative isolation’ (p. 177) becomes particularly evident in the discussion on water-balance physiology. Why choose to ignore aquatic insects when presenting metabolism and gas exchange and then include them in a review of their responses to osmotic stress?

The two chapters on temperature limits and thermoregulation discuss challenging questions and are the best of this book. They adequately review various aspects of insects’ adaptations and limitations. A more extensive discussion of adaptations to higher temperatures, beyond the Drosophila example would have been welcome.

Considering the importance of environmental changes on the evolutionary process, the authors have succinctly addressed the important issue of climate change and its current and future impacts on insect distribution. As the climate warms up, many insect species extend their range and may migrate, a phenomenon that requires proper physiological adjustments. The authors identify a number of important areas requiring further research. The examples discussed throughout the book reveal a dire need for more physiological ecology studies on insects of the southern hemisphere. Hopefully the book will trigger more interest in the insects of the southern half of the planet.

In spite of its shortcomings Chown and Nicolson's book will be a contribution welcomed by researchers and professors. It should particularly appeal to graduate students involved in both physiological and ecological studies of insects, in two disciplines that are complementary for developing a better understanding of insects’ evolution and success. It will also be an excellent source of information for teaching at both the undergraduate and graduate levels.