Ecology of Freshwater Nematodes

Walter Traunspurger

• Publisher: CAB International
• Year: 2021
• Print ISBN: 9781789243635
• eBook ISBN: 9781789243659
• Topic: Biological Sciences
• Subtopic: Ecology
• Index: Biological Sciences

Nematodes are incontestably the most numerous and the most diverse metazoans in freshwater habitats, and these properties bestow exceptional significance to their role in the environment. An array of functional roles has been attributed to them: they are grazers on bacteria and primary producers, regulators of decomposition of plant material, predators, prey for other animals, and closely associated symbionts of bacteria and other organisms.Freshwater nematodes are central in the context of environmental monitoring, pollution assessments, global warming and food webs, and this is increasingly being recognized. Moreover, the short generation time (a few days to months) of many species makes nematodes ideal for laboratory studies. This book: Provides a follow-up to Freshwater Nematodes: Ecology and Taxonomy (2006).Offers guidelines for studying the ecology of free-living nematodes, including detailed protocols and case studies.Promotes free-living nematodes as model organisms for studies in a broad range of research fields.Despite the recognized importance of nematodes across ecosystems, many species of free-living nematodes have yet to be discovered, and essential knowledge gaps remain. Ecology of Freshwater Nematodes provides an overview of research efforts in this field, and is an important resource for researchers in the field of nematology and ecology.

1 Introduction to Freshwater Nematodes in Ecology: Current Knowledge and Research

NABIL MAJDI AND WALTER TRAUNSPURGER

Animal Ecology, Bielefeld University, Bielefeld, Germany

1.1 A Short Summary of Nematode Morphology and Reproduction

1.2 What Is the Role of Nematodes in Freshwater Ecosystems?

1.2.1 A brief history and definition of ecology

1.2.2 Distribution and dispersal of free-living nematodes

1.2.3 Role of free-living nematodes in food webs

1.3 Why This Book?

1.3.1 The relevance of ecology in nematology

1.3.2 An overview of the book’s content

1.4 Species Diversity and an Overview of Nematode Classification

1.4.1 Torquentia Andrássy, 1974

1.4.2 Secernentia Linstow, 1905

1.4.3 Penetrantia Andrássy, 1974

Highlights

• Nematodes are tiny roundworms that abound in most parts of the biosphere.

• They show remarkably diverse life strategies and occupy important positions in food webs.

• Their role in ecosystems has nonetheless been largely ignored by ecologists and nematologists.

• This book offers guidelines for studying the ecology of free-living nematodes, with the aim of increasing interest in this topic in current and future generations of scientists.

1.1 A Short Summary of Nematode Morphology and Reproduction

Nematodes are tiny roundworms, usually elongated, bilaterally symmetrical, and rod- or thread-like in shape. They comprise the ‘phylum’ Nematoda, the name of which derives from a Latinized form of the Greek words nema- (meaning thread) and -eidos (meaning form or resemblance) (Andrássy, 2005). Most species are microscopic and translucent, with the body lengths of most freshwater species ranging between 0.3 and 5 mm. Parasitic species may be much larger depending on the size of their host. For example, the body length of the largest nematode described so far, Placentonema gigantissima, a parasite of sperm whales, may exceed 6–8 m (Gubanov, 1951).

The nematode body wall is composed of an outer non-cellular sheath (the cuticle), an inner syncytial layer (the hypodermis), and the somatic musculature. The body wall determines the shape of the nematode, serves as a barrier to external physico-chemical obstacles, biotic agents, and pathogens, enables direct contact between the worm and its environment, and allows the exchange of fluids and gases into and out of the nematode’s body (Andrássy, 2005). The surface of the cuticle may be entirely smooth (as observed by light microscopy) or marked by various transverse or longitudinal structures (Fig. 1.1a,b). During nematode ontogenesis, from egg to adult, the cuticle normally is shed four times (molting or ecdysis).

Fig. 1.1. Examples of representative morphological characteristics of freshwater nematodes: (a) and (b) cuticle ornamentation; (c) and (d) anterior part showing papillae, lips, and other cephalic setae; (e), (f), and (g) head with inner mouth structures; (h) amphid; (i) and (k) examples of esophagus shape; (l) and (m) female genital system; (n), (o), and (p) male genital system.

The general cavity contains an alimentary tract made up of a mouth or oral aperture (Fig. 1.1c–g) and amphid (Fig. 1.1h), followed by an esophagus (Fig. 1.1i,k) and an intestine that opens to the outside via an anus. The excretory system of nematodes is unparalleled among invertebrates because it does not rely on cilia, flame cells, or protonephridia. The nervous system of Nematoda is rather complex. It mainly consists of a central part. The nerve ring (‘brain’), and a number of (predominantly six) nerve chords extending anteriorly or posteriorly through the entire body. The longitudinal nerves are then provided with several ganglia.

The female genital system differs substantially from that of the male. In the female, the genital tube or gonad consists of the ovaries, oviducts, uterus (with or without eggs), spermatheca, and vagina (Fig. 1.1l,m). It opens through a separate pore, the vulva, on the ventral side of the body. The male genital system consists of a larger number of sexual characters or structures and is made up of primary and secondary organs. The former includes the testis, seminal vesicle, ejaculatory duct, cloacal chamber, and associated glands, and the latter the copulatory muscles, spicula, gubernaculum, guiding pieces, genital papillae, supplementary organs, and bursa (Fig. 1.1n–p). Most nematode species are bisexual (especially marine nematode species). Sex ratios are variable, but for most free-living nematode species females and males occur in near equal abundance. In other nematode genera and species males are much fewer in number (e.g. Eumonhystera spp., Plectus spp.). For example, in Rhabdolaimus spp. the male:female ratio is typically 1:1000. Moreover, there are several species, such as Bunonema, in which only females are found, with males either thus far unobserved because of their rarity or their complete absence. Some of these species are capable of parthenogenesis, a process of monosexual reproduction in which progeny develop from unfertilized ova (eggs), without the participation of male genital cells (spermatozoa). Monosexual reproduction is also exhibited by the few species that are hermaphroditic, especially those belonging to the Secernentia (Andrássy, 2005). In this case, the hermaphrodite parent, a female-like individual with the usual external (and internal) female characters, produces both eggs and sperm and reproduction occurs through self-fertilization.

1.2 What Is the Role of Nematodes in Freshwater Ecosystems?

1.2.1 A brief history and definition of ecology

Free-living nematodes are widespread in inland waters. Their diverse morphologies and life strategies, as briefly discussed above, reflect their many functions in freshwater ecosystems, the main subject of this book. Although ecology emerged with the Industrial Revolution and the changes in human society that accompanied it, ecological questions were already being posed two millennia earlier. Both Aristotle and Pliny the Elder contemplated the relationship between living beings and their environment as well as the role of humans in the balances of nature. The natural histories developed by these philosophers remained unchallenged until the emergence of the classification system of Linnaeus, the publication of Malthus’ An Essay on the Principle of Population, the biogeographical reports of Humboldt, the economics of Liebig, and, especially, Darwin’s theory of evolution. Together, these works gave rise to the definition of ecology proposed in 1866 by Haeckel: ‘Ecology is the science of the relations of living beings, plants and animals, between them and with their environment’. But it was not until the beginning of the 20th century that a more rigorous approach to ecology emerged. Important ecologists, among others, during the past 100 years are: Alfred J. Lotka and Vito Volterra, who, working independently, developed predator–prey models; Vladimir Vernadski, who introduced the biogeochemical concept of ‘biosphere’; Arthur G. Tansley, who introduced the concept of ...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• Dedication
• Contents
• List of Contributors
• Preface
• 1 Introduction to Freshwater Nematodes in Ecology: Current Knowledge and Research
• 2 Sampling and Processing of Freshwater Nematodes with Emphasis on Molecular Methods
• 3 Species Composition and Distribution of Free-living Nematodes in Lakes and Streams
• 4 Nematodes from Extreme and Unusual Freshwater Habitats
• 5 Dispersal of Free-living Nematodes
• 6 Feeding Ecology of Free-living Nematodes
• 7 Role of Nematodes in the Food Web: Nematodes as Predator and Prey
• 8 Production of Freshwater Nematodes
• 9 Freshwater Nematodes in Metacommunity Studies
• 10 Single- and Multi-species Toxicity Testing with Nematodes
• 11 Freshwater Nematodes as Bioindicators in Field Studies – The NemaSPEAR[%]-index
• 12 Case Studies with Nematodes from the Individual to Ecosystem Level
• Index
• Cabi
• Back