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Locomotion of Animals PDF

169 Pages·1982·3.814 MB·English
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Locomotion of Animals TERTIARY LEVEL BIOLOGY A series covering selected areas of biology at advanced undergraduate level. While designed specifically for course options at this level within Universities and Polytechnics, the series will be of great value to specialists and research workers in other fields who require a knowledge of the essentials of a subject. Titles in the series: Experimentation in Biology Ridgman Methods in Experimental Biology Ralph Visceral Muscle Huddart and Hunt Biological Membranes Harrison and Lunt Comparative Immunobiology Manning and Turner Water and Plants Meidner and Sheriff Biology of Nematodes Croll and Matthews An Introduction to Biological Rhythms Saunders Biology of Ageing Lamb Biology of Reproduction Hogarth An Introduction to Marine Science Meadows and Campbell Biology of Fresh Waters Maitland An Introduction to Developmental Biology Ede Physiology of Parasites Chappell Neurosecretion Maddrell and Nordmann Biology of Communication Lewis and Gower Population Genetics Gale Structure and Biochemistry of Cell Organelles Reid Developmental Microbiology Peberdy Genetics of Microbes Bainbridge Biological Functions of Carbohydrates Candy Endocrinology Goldsworthy, Robinson and Mordue The Estuarine Ecosystem McLusky Animal Osmoregulation Rankin and Davenport Molecular Enzymology Wharton and Eisenthal Environmental Microbiology Grant and Long The Genetic Basis of Development Stewart and Hunt TERTIARY LEVEL BIOLOGY Locomotion of Animals R. McNeill Alexander, D.Sc. Professor of Zoology University of Leeds Blackie Glasgow and London Distributed in the USA by Chapman and Hall New York Blackie & Son Limited Bishopbriggs, Glasgow G64 2NZ Furnival House, 14-18 High Holborn, London WC1 V 6BX Distributed in the USA by Chapman and Hall, 733 Third Avenue, New York, N.Y. 10017 in association with Methuen, Inc. © 1982 ~Iackie & Son Limited First published 1982 Softcover reprint of the hardcover 1s t edition 1982 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, recording or otherwise, without prior permission of the Publishers British Library Cataloguing in Publication Data Alexander, R. McNeill Locomotion of animals.-(Tertiary level biology) 1. Animal locomotion I. Title II. Series 591 .1 '852 OP301 ISBN-l3: 978-94-011-6011-7 e-ISBN-13: 978-94-011-6009-4 DOl: lO.lO07/978-94-011-6009-4 For the USA, International Standard Book Numbers are cloth 0-412-00001-6 paper 0-412-00011-3 Filmset by Advanced Filmsetters (Glasgow) Ltd Preface This book is about how animals travel around on land, in water and in the air. It is mainly about mechanisms of locomotion, their limitations and their energy requirements. There is some information about muscle physiology in Chapter 1, but only as much as seems necessary for the discussions of mechanisms and energetics. There is information in later chapters about the patterns of repetitive movement involved, for instance, in different gaits, but nothing about nervous mechanisms of coordination. I have tried to include most ofthe widely-used methods of locomotion, but have not thought it sensible to try to mention every variety of locomotion used by animals. This book is designed for undergraduates, but I hope that other people will also find it interesting. It is possible and sometimes illuminating to use complex mathematics in discussions of animal locomotion. This book includes many equations, but little mathematics. Such mathematics as there is, is simple. Discussions of the mechanisms and energetics of locomotion inevitably involve mechanics. I expect that some readers will know a lot of mechanics, and some hardly any. I have tried to help the latter without boring the former, by putting a summary of the necessary mechanics in an appendix (p. 140). References from the main text to the appendix will tell readers where they can find help, if they need it. Figures and equations in the appendix have numbers distinguished by a prefix A (for instance, Figure A.3). There is a list of references and suggestions for further reading at the end of the book. References in the text indicate principal sources of information, but I have not thought it desirable to insert the much larger number of references that would be needed to show the authority for every statement. Dr H. C. Bennet-Clark and Dr C. J. Pennycuick read the typescript and made many very helpful suggestions. R. McNeill Alexander v Contents Chapter 1 SOURCES OF POWER 1 Muscle. Types of muscle. Arrangement of muscles. Other sources of power. Chapter 2 SWIMMING 13 Swimming by undulation. Rowing. Swimming with hydrofoils. Jet propulsion. Chapter 3 BUOYANCY 39 Dense animals. Low-density materials. Gas-filled floats. Buoyancy and ways of life. Advantages of different buoyancy aids. Chapter 4 FLIGHT 54 Gliding. Soaring. Fast flapping flight. Hovering and slow flight. Take-off and landing. Chapter 5 WALKING, RUNNING AND JUMPING 81 Walking slowly. Walking faster. Running bipeds. Running quad- rupeds. Energetics. Stance. Climbing. Jumping. Chapter 6 CRAWLING 114 Two-anchor crawling. Peristalsis. Pedal waves. Serpentine crawl- ing. Amoeboid crawling. Chapter 7 LOCOMOTION IN GENERAL 126 Comparisons. Escape and capture. Herds, flocks and shoals. Appendix BASIC MECHANICS 140 Units. Vectors. Movement. Force. Energy. Properties of materials. Similarity. Bodies in fluids. REFERENCES AND FURTHER READING 154 INDEX 159 Vll CHAPTER ONE SOURCES OF POWER The movements described in this book are powered by muscles, cilia, flagella or cytoplasmic streaming. This chapter is mainly about muscle but includes brief accounts of the other sources of power. Muscle Muscle fibres do work by shortening while exerting a force. The structures that generate force have been identified in electron microscope sections and are shown diagrammatically in Figure l.la,b (see also White, 1977). They are protein filaments a few micrometres long, arranged parallel to the length of the fibre. There are thick filaments of myosin and thin ones of actin and tropomyosin. The muscles that move the skeletons of vertebrates and insects are of the cross-striated kind shown in the figure. Interdigitating bands of thick and thin filaments alternate along the length of the fibre, and partitions called Z-discs cross the fibre, through the mid points of the thin filaments. Each repeat of the resulting pattern of stripes is called a sarcomere. A different, obliquely-striated type of muscle fibre is found in nematode and annelid worms and in many of the muscles of molluscs. Its sarcomeres run obliquely across the fibre. The thick filaments have projections called cross-bridges that seem to be capable of attaching to a thin filament and then swinging through an angle, making the filaments slide past each other. They can detach, swing back and reattach to a different point on the thin filament. In this way the cross-bridges can pull on the thin filaments like a man pulling in a rope hand over hand. Each sarcomere can be shortened from the state shown in Figure l.1a to that shown in Figure l.1b. Notice that if the sarcomere were stretched beyond the state shown in Figure l.1a the thin filaments 1 g nin ed. e n , , , , \ rate of short siderably shortening. -, , 'power, , c ed and in (b) conwhich it is shorte - ndat /I muscle is exted on the rate I I he pen n (a) tert de Ix muscle. e can e d scl eu atm f cross-striwer that a 1-: / b dinal section oe force and po " "ents nts 1 arcomere 1 of a longituwing how th " thick filam thin filame / Z-disc f --'I" one s .. a (a, b) Diagrams ematic graph sho 'I' ,t e 1.1 A sch gur(c) Fi SOURCES OF POWER 3 would be pulled right out from between the thick ones and the cross bridges could no longer attach. Also, sarcomeres cannot shorten much beyond the point shown in Figure 1.1 b because the thick filaments abut against the Z-discs. Therefore, cross-striated muscle can operate only over a limited range of lengths: the minimum length is not much less than half the maximum. There is an intermediate length at which all the cross bridges can attach but none of the disadvantages of excessive shortening operate. This is the length at which most force can be exerted. Since the cross-bridges transmit the force from the thick filaments to the thin ones, the force that a muscle fibre can produce is proportional to the number of cross-bridges in each sarcomere. Muscles with long filaments can therefore exert more stress than muscles with shorter ones. Vertebrate skeletal muscles have thick filaments about 1.61lm long and can exert maximum stresses of about 0.3 MPa, * but locust leg muscle has filaments about 5.5 11m long and can exert 0.8 MPa. Imagine (if you can) a vertebrate muscle of volume 1 m3• When this particular muscle is fully extended its fibres are 1.4 m long, and when it is fully shortened they are just half as long, or 0.7 m. About halfway through the contraction the fibres are 1 m long so the cross-sectional area is 1 m2, and if the stress is OJ MPa the force is 0.3 MN. The fibres shorten by 0.7 m while exerting this force, so the work done is 0.7 x 0.3 = 0.21 MJ. The mass of 1 m3 muscle would be about 1000 kg, so this work is 210 J per kg muscle. This is a very crude argument, but a more precise one leads to a similar conclusion. Vertebrate skeletal muscle cannot do more work than about 200 J /kg in a single contraction. There is a limit to the rate at which cross-bridges can attach, pull and detach again. There is therefore a limit to the rate at which they can make the filaments slide past each other. The rate varies in different muscles: let it be u in a muscle fibre that has length I when its sarcomeres have length A.. Each sarcomere can shorten at a speed 2u and the fibre as a whole can shorten at 2ul/), because it has 1/), sarcomeres. The fastest known muscles seem to be a rat eye muscle and a mouse toe muscle, which can shorten at rates corresponding to 25 fibre lengths per second (i.e. 2u/ A = 25 s -1 ). Mammal muscles have sarcomeres about 2.5 11m long, so this implies a sliding speed u of about 30llm/s. Notice that the rate of shortening of the fibre would be less (for given u) if the sarcomere were longer. Long sarcomeres give high stresses but low rates of shortening. The faster a muscle is shortening, the less force it can exert. Conversely, * A megapascal (MPa) is one million newtons per square metre or 102 grams weight per square millimetre. See the explanation of units in the appendix. 4 LOCOMOTION OF ANIMALS the less resistance it experiences, the faster it can shorten (Figure 1.1c). The maximum stress of 0.3 MPa exerted by typical vertebrate skeletal muscles can be exerted only when the muscle is shortening very slowly or not at all. The maximum work of 200 J kg - can therefore be done only in a very 1 slow contraction. The maximum speed of shortening (25 lengths s - 1 ) given above for the fastest rat and mouse muscles can be achieved only when no external load acts on the muscle. The power output of a muscle is the force it exerts multiplied by the rate of shortening. At the highest rate of shortening no force is developed, so the power is zero. A large force can be exerted if the rate of shortening is zero but the power is then again zero. Power output is greatest at an intermediate speed (Figure 1.1c). The flight muscles of various insects and hummingbirds have been shown to be capable of power outputs of about 200 W per kg muscle-this is the mean power output over a series of cycles of contraction and relaxation, and no muscles are known to produce much more power than this. These muscles work aerobically, and have up to about half of their volume occupied by mitochondria. It is possible that a very fast anaerobic muscle containing fewer mitochondria and more thick and thin filaments could produce more power. Aerobic and anaerobic muscles are discussed in the next section of this chapter. A muscle that shortens while exerting a force does (positive) work. One that is forcibly extended while exerting a force has work done on it and degrades this work to heat Gust as work is degraded to heat in the brakes of a vehicle). This is often described by saying that the muscle does negative work. Figure 1.1c shows that large forces cause lengthening (negative rates of shortening) of muscles. Muscles have to do negative work when a running animal slows down, or decelerates a moving limb. The rates at which animals use chemical energy can be calculated from their rates of oxygen consumption (unless anaerobic metabolism is being used). This is the basis for many measurements of muscle efficiency. For instance, the rates of oxygen consumption have been measured for people resting and doing work at a known rate by pedalling a bicycle ergometer. The difference gave the metabolic power used for pedalling, so the efficiency could be calculated as (mechanical power output) -;- (metabolic power consumption). This experiment showed that over a wide range of rates of pedalling, the efficiency of doing positive work is about 0.25. Measurements of the rates of oxygen consumption of people, squirrels and other mammals running up steep gradients, and of birds flying up gradients in wind-tunnels, have confirmed that muscle can do positive work with efficiencies up to about 0.25. (Experiments involving running up

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