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Insect Physiological Ecology This page intentionally left blank Insect Physiological Ecology Mechanisms and Patterns Steven L. Chown University of Stellenbosch Sue W. Nicolson University of Pretoria 1 1 Great Clarendon Street, Oxford OX2 6DP Oxford University Press is a department of the University of Oxford. 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ISBN 0 19 851548 0 (Hbk) ISBN 0 19 851549 9 (Pbk) 10987654321 Preface Living in the Southern Hemisphere has several differences are not only biologically interesting, advantages. It means ready access to relatively but might also have profound consequences for wild, undisturbed, and animal-rich areas, a climate the way in which humans attempt to manage the where the seasonal variation is usually not vast but global experiment they have set in motion. where every year brings something of a surprise, Like most other authors we have an intellectual and an extensive body of water, the Southern debt. We owe much of the way we think about Ocean, that is alive with riches should one choose the world to discussions with Andy Clarke, Peter to venture out onto it. However, living in the south Convey, Trish Fleming, Kevin Gaston, Allen Gibbs, also has several disadvantages. Like-minded scien- Sue Jackson, Jaco Klok, John Lighton, Gideon Louw, tists often live a day or more’s travel away, editors Lloyd Peck, Brent Sinclair, Ken Storey, Ben-Erik have until recently tended to view the equator as Van Wyk, and Karl Erik Zachariassen. We are something of an asymmetric barrier, and local grateful to them for the insights they have readily biological meetings almost inevitably leave certain contributed. SLC is particularly indebted to areas, such as insect physiology, scratching about Kevin Gaston for sharing many ideas and for the for an audience, if not for speakers. It is the latter thousands of messages that have crossed the disadvantage that provided the initial impetus for equator. Brent Sinclair and Ken Storey gave us this book. The field of insect physiological ecology, permission to use figures they had drawn. Kevin at least in southern Africa, is small. In consequence, Gaston, Allen Gibbs, Ary Hoffmann, Sue Jackson, we regularly found ourselves in the same sessions Melodie McGeoch, Brent Sinclair, Graham Stone, at the biennial zoological or entomological meet- and Art Woods read one or more chapters or ings, each presenting a rather different perspective the entire manuscript. We are grateful for their on physiological ecology: one more mechanistic, comments, which were helpful, challenging and the other more comparative. Our interactions over insightful. at least a decade of meetings, both locally and We thank the following for permission to repro- abroad, have shown that these perspectives have duce figures from works they have published: much to offer each other. Moreover, our discussions Academic Press, the American Association for the have mirrored a growing realization in the field as Advancement of Science, the American Institute of a whole that an integration of mechanistic and Biological Sciences, the American Physiological broader-scale comparative physiology can result in Society, Blackwell Publishing, Cambridge novel and unexpected insights. One of the main University Press, the Company of Biologists, the points of this book is to explore these insights. Ecological Society of America, Elsevier, Kluwer, the Along the way, we also hint at the idea that the National Academy of Sciences of the USA, Oxford Southern Hemisphere might differ from the north University Press, the Royal Society, the Society for in more ways than those alluded to above. These Integrative and Comparative Biology, the Society vi PREFACE for the Study of Evolution, Springer-Verlag, the by our recent moves around South Africa, and one University of Chicago Press and Wiley Interscience; of us being appointed to departmental chair. also Tim Bradley for permission to reproduce Our families were uniformly supportive, and Fig. 4.8. We are grateful to Sheena McGeoch and endured busy weekends and few holidays, for Anel Garthwaite for assistance with the figures. which we are grateful. Ian Sherman and Anita Petrie looked after pub- lication. Ian provided much encouragement and Stellenbosch and Pretoria advice throughout the project, and was unperturbed December 2003 Contents 1 Introduction 1 1.1 Physiological variation 2 1.2 How much variation? 3 1.3 Diversity at large scales: macrophysiology 7 1.4 Growing integration 9 1.5 This book 10 2 Nutritional physiology and ecology 14 2.1 Method and measurement 16 2.1.1 Artificial diets 16 2.1.2 Indices of food conversion efficiency 16 2.1.3 Use of a geometric framework 17 2.2 Physiological aspects of feeding behaviour 18 2.2.1 Optimal feeding in caterpillars 18 2.2.2 Regulation of meal size: volumetric or nutritional feedback 20 2.2.3 Regulation of protein and carbohydrate intake 22 2.3 Digestion and absorption of nutrients 23 2.3.1 Digestive enzymes and the organization of digestion 23 2.3.2 Gut physicochemistry of caterpillars 26 2.3.3 Absorption of nutrients 27 2.4 Overcoming problems with plant feeding 30 2.4.1 Cellulose digestion: endogenous or microbial? 30 2.4.2 Nitrogen as a limiting nutrient 32 2.4.3 Secondary plant compounds 34 2.5 Growth, development, and life history 39 2.5.1 Development time versus body size 39 2.5.2 Developmental trade-offs between body parts 41 2.6 Temperature and growth 44 2.6.1 Thermal effects on feeding and growth 44 2.6.2 Interactions with food quality 46 3 Metabolism and gas exchange 49 3.1 Method and measurement 50 3.2 Metabolism 51 3.2.1 Aerobic pathways 51 3.2.2 Anaerobic pathways and environmental hypoxia 52 viii CONTENTS 3.3 Gas exchange structures and principles 54 3.3.1 Gas exchange and transport in insects 55 3.3.2 Gas exchange principles 57 3.4 Gas exchange and metabolic rate at rest 60 3.4.1 Gas exchange patterns 60 3.4.2 Discontinuous gas exchange cycles 63 3.4.3 Variation in discontinuous gas exchange cycles 66 3.4.4 Origin and adaptive value of the DGC 68 3.4.5 Metabolic rate variation: size 73 3.4.6 Metabolic rate variation: temperature and water availability 75 3.5 Gas exchange and metabolic rate during activity 79 3.5.1 Flight 80 3.5.2 Crawling, running, carrying 83 3.5.3 Feeding 85 3.6 Metabolic rate and ecology 86 4 Water balance physiology 87 4.1 Water loss 87 4.1.1 Cuticle 88 4.1.2 Respiration 91 4.1.3 Excretion 94 4.2 Water gain 99 4.2.1 Food 100 4.2.2 Drinking 101 4.2.3 Metabolism 102 4.2.4 Water vapour absorption 102 4.3 Osmoregulation 103 4.3.1 Haemolymph composition 103 4.3.2 Responses to osmotic stress 105 4.3.3 Salt intake 107 4.4 Desiccation resistance 107 4.4.1 Microclimates 108 4.4.2 Group effects 109 4.4.3 Dormancy, size, and phylogeny 109 4.5 The evidence for adaptation: Drosophila as a model 111 5 Lethal temperature limits 115 5.1 Method and measurement 115 5.1.1 Rates of change 117 5.1.2 Measures of thermal stress 118 5.1.3 Exposure and recovery time 120 5.2 Heat shock, cold shock, and rapid hardening 121 5.2.1 Acclimation 122 5.2.2 Heat shock 124 5.2.3 Cold shock 131 5.2.4 Relationships between heat and cold shock responses 134 CONTENTS ix 5.3 Programmed responses to cold 137 5.3.1 Cold hardiness classifications 137 5.3.2 Freeze intolerance 139 5.3.3 Cryoprotective dehydration 144 5.3.4 Freezing tolerance 145 5.4 Large-scale patterns 146 5.4.1 Cold tolerance strategies: phylogeny, geography, benefits 147 5.4.2 The geography of upper and lower limits 150 6 Thermoregulation 154 6.1 Method and measurement 155 6.2 Power output and temperature 157 6.3 Behavioural regulation 160 6.3.1 Microhabitats and activity 161 6.3.2 Colour and body size 163 6.3.3 Evaporative cooling in ectothermic cicadas 165 6.4 Butterflies: interactions between levels 166 6.4.1 Variation at the phosphoglucose isomerase locus 167 6.4.2 Wing colour 167 6.4.3 The influence of predation 168 6.5 Regulation by endothermy 169 6.5.1 Preflight warm-up 170 6.5.2 Regulation of heat