Table Of ContentA FUNCTIONAL BIOLOGY OF NEMATODES
FUNCTIONAL BIOLOGY SERIES
General Editor: Peter Calow, Department of Zoology,
University of Sheffield
A Functional Biology of Free-living Protozoa
Johanna Laybourn-Parry
A Functional Biology of Sticklebacks
R.J. Wootton
A Functional Biology of Marine Gastropods
Roger N. Hughes
A Functional Biology of Nematodes
David A. Wharton
F".ctio,",l
A
Biology
of
Nematodes
David A. Wharton, PhD,
Lecturer in Zoology,
University of Otago,
New Zealand
qp
CROOM HELM
London & Sydney
© 1986 David A. Wharton
Softcover reprint of the hardcover 1st edition 1986
Croom Helm Ltd, Provident House, Burrell Row,
Beckenham, Kent BR3 1AT
Croom Helm Australia Pty Ltd, Suite 4, 6th Floor,
64-76 Kippax Street, Surry Hills, NSW 2010, Australia
British Library Cataloguing in Publication Data
Wharton, David A.
A functional biology of nematodes.
1. Nematoda
I. Title
595.1'82 QL391.N4
TSBN-I3: 978-1-4615-8518-3 e-TSBN-I3: 978-1-4615-8516-9
DOl: 1O.lO07/978-1-4615-8516-9
Typeset in lOpt Times Roman by Leaper & Gard Ltd, Bristol, England
Biddies Ltd, Guildford and King's Lynn
CONTENTS
Series Foreword
Preface
1. Introduction 1
2. Functional Organisation 9
3. Movement and Co-ordination 35
4. Reproductive Biology 60
5. Parasitism 88
6. LifeCycle 118
7. Environmental Physiology 149
References 171
Index 185
For Ann
FUNCTIONAL BIOLOGY SERIES: FOREWORD
General Editor: Peter Calow, Department of Zoology, University of Sheffield,
England
The main aim of this series will be to illustrate and to explain the way
organisms 'make a living' in nature. At the heart of this - their
functional biology - is the way organisms acquire and then make use
of resources in metabolism, movement, growth, reproduction, and so
on. These processes will form the fundamental framework of all the
books in the series. Each book will concentrate on a particular taxon
(species, family, class or even phylum) and will bring together
information on the form, physiology, ecology and evolutionary
biology of the group. The aim will be not only to describe how
organisms work, but also to consider why they have come to work in
that way. By concentrating on taxa which are well known, it is hoped
that the series will not only illustrate the success of selection, but also
show the constraints imposed upon it by the physiological, morpho
logical and developmentallimhations of the groups.
Another important feature of the series will be its organismic
orientation. Each book will emphasise the importance of functional
integration in the day-to-day lives and the evolution of organisms.
This is crucial since, though it may be true that organisms can be
considered as collections of gene-determined traits, they neverthe
less interact with their environment as integrated wholes and it is in
this context that individual traits have been subjected to natural
selection and have evolved.
The key features of the series are, therefore:
(1) Its emphasis on whole organisms as integrated, resource-using
systems.
(2) Its interest in the way selection and constraints have moulded
the evolution of adaptations in particular taxonomic groups.
(3) Its bringing together of physiological, morphological, eco
logical and evolutionary information.
P.Calow
PREFACE
I am continually surprised and delighted by the variety and beauty
of the adaptations that enable nematodes to exploit their various
habitats. Sometimes these are almost unbelievable. Some nema
todes can remain active for several hours in fixative, and can
survive exposure to extreme desiccation and vacuum, and the eggs
of some species can survive exposure to concentrated sulphuric
acid. The ability to survive periods of exposure to adverse environ
mental conditions has enabled nematodes to exploit almost every
conceivable habitat. For activity, growth and reproduction to
occur, however, at least a film of water must be present.
The economic importance of parasitic nematodes has focused
attention on these, rather than free-living species. Despite the
abundance of free-living nematodes, they have been relatively little
studied, and this book, of necessity, reflects this imbalance. It has,
however, been my intention to examine the biology of the phylum
as a whole and, where possible, examples have been drawn from
animal parasitic, plant parasitic and free-living species. The free
living nematode Caenorhabditis elegans has in recent years been
adopted as a convenient model to study important problems in the
developmental genetics and biology of metazoans. Clearly, our
knowledge of the biology of free-living nematodes and of nema
tode biology as a whole will increasingly be based on this species.
Any author attempting to write on a group as widespread as the
Nematoda is in danger of being overwhelmed by the volume of
information which he unearths. My approach has been to try to
provide an overview of the features of the biology of nematodes
which seem to me to be important. Above all I have attempted to
show how nematodes work as integrated wholes, and how they are
able to live in the habitats they do. I have not tried to give detailed
descriptions of nematode morphology and the structural variations
between species, but have tried to provide references where such
details can be found. I hope that enough morphological detail has
been provided to enable the functional organisation of nematodes
to be understood.
Many people have helped and encouraged me in the writing of
the book. Thanks are due especially to Professor John Barrett,
Preface
without whose aid and advice over the past few years I would
never have been in a position to undertake such a task. Thanks
also to John Barrett, Stephen Young, Ann Wharton, Rolo Perry,
Tim Hardwick and Peter Calow who read the entire manuscript,
and to Bob Wootton, Adrian Hopkins, Lloyd Davis, Mike Barker,
Rod Turner, Marcus Trett and Chris Preston who read parts of it.
Julia Bowler drew or completed the drawing of most of the figures
and Jean Clough drew some of the figures in Chapter 6. The
following kindly provided me with copies of published figures
and/or plates: Dr D.J. McLaren, Dr AM. Shepherd, Dr c.c.
Doncaster, Dr R.1. Sommerville, Dr J. Giebel, Dr M.G.K. Jones,
Dr T. Jenkins, Dr H.C. Bennet-Clark, Dr E.A Munn, Professor
K.A Wright, Dr P.AG. Wilson, Professor H.R. Wallace, Dr J.G.
White and Dr C.M. Preston. The sources of redrawn figures and
published data are acknowledged in the text. I would also like to
thank the following for permission to reproduce material:
Academic Press, Macmillan Publishers, Cambridge University
Press, Pergamon Press, Annual Reviews Inc., Longman Group
Ltd, Annals of Applied Biology, Zoological Society of London,
Society of Nematologists, Elsevier/North Holland Press, and the
Royal Society of London. The sources of published figures and
plates are given in the text.
David A Wharton
1 INTRODUCTION
Within the animal kingdom, nematodes are second only to the
arthropods both in the numbers of species and in the numbers of
individuals present. Indeed, they are so numerous that, in a famous
quote, Cobb (1915) was led to comment:
If all the matter in the universe except the nematodes were
swept away, our world would still be dimly recognisable, and if,
as disembodied spirits, we could investigate it, we should find its
mountains, hills, vales, rivers, lakes and oceans represented by a
thin film of nematodes ...
Although they have a relatively constant body form, nematodes
have successfully exploited a wide variety of habitats. They are
parasites of almost every species of animal and plant. Free-living
species live in the soil, and in freshwater and marine habitats. They
may be bacterial-feeders, fungal-feeders, algal-feeders, herbivores,
omnivores, parasites or predators. They are found in hot springs,
were thawed out from the Antarctic ice by members of the
Shackleton expedition, and can survive complete desiccation and
exposure to high vacuum. Their only limiting factor appears to be
that, although some species can survive desiccation, activity is
limited to environments where they are surrounded by at least a
film of water.
Approximately 48 per cent of nematode genera are parasites of
animals and plants (Table 1.1). The remainder are free-living in
the soil and in freshwater or marine sands and muds') These figures
are probably heavily biased towards parasitic nematodes. The large
number of genera of vertebrate parasites reflects the amount of
study that has been devoted to this group as well as the richness of
the fauna. (Around 1500 to 1600 nematode species have been
described, and it has been esti91ated that there are about 42000
species in total)(Poinar, 1983). Free-living nematodes have been
relatively little studied, and it is clear that many species remain to
be discovered. Parasitic species may, therefore, be heavily out
numbered by free-living species.
Despite the ubiquity of nematodes they rarely reach the con-
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