Spider Communication: Mechanisms and Ecological Significance

by Peter N. Witt, Jerome S. Rovner

Overview

Concentrating on the complex spider communication system, this book assembles the most recent multidisciplinary advances of leading researchers from many countries to assess the peculiar role spiders play in the animal kingdom.

Originally published in 1982.

The Princeton Legacy Library uses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These editions preserve the original texts of these important books while presenting them in durable paperback and hardcover editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.

Product Details

ISBN-13:	9780691642154
Publisher:	Princeton University Press
Publication date:	04/19/2016
Series:	Princeton Legacy Library , #536
Pages:	452
Product dimensions:	6.20(w) x 9.30(h) x 1.20(d)

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Spider Communication

Mechanisms and Ecological Significance

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By Peter N. Witt, Jerome S. Rovner

PRINCETON UNIVERSITY PRESS

Copyright © 1982 Princeton University Press
All rights reserved.
ISBN: 978-0-691-08291-2

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CHAPTER 1

INTRODUCTION: COMMUNICATION IN SPIDERS

Peter N. Witt
North Carolina Mental Health Research
Anderson Hall
Dorothea Dix Hospital
Raleigh, North Carolina 27611

Most of the authors of this book were invited by me to come together as part of the International Meeting sponsored by the American Arachnological Society in the summer of 1978 in Gainesville, Florida. They agreed to discuss their work as it contributed to our knowledge about communication in spiders. I conceived the plan for the book at the symposium and thus became its senior editor. At a later date I asked Jerome Rovner to join me in the editorial work, and we bear together the responsibility for the present list of contributors and the present shape. The final version developed after the symposium through additional reviews of the relevant literature and inclusion of current laboratory and field work. All along we tried to preserve the attraction of the immediateness of the reports from the authors' own laboratories and combine them with a more general review of the field. The text aims at presenting the present state of knowledge and is a compromise between completeness and readability. Sometimes a chapter fits only the widest definition of "communication," e.g., Riechert and-Luczak's "Spider Foraging: Behavioral Responses to Prey." Because it contains valuable information on spider behavior and ecology which is not to be found summarized elsewhere, and because it rounds off the other chapters by applying some of the sensory physiology and other knowledge to predator-prey interactions, the editors decided to include it. After all, the subject matter of that chapter is an important part of the spider's relationship with its environment. A special effort is made to address readers beyond arachnologists, so that they can sample and compare how much (or little) is known about one aspect of this one group of animals at the present time.

To many readers opening this volume, the title will seem strange, if not unworthy of serious and lengthy treatment. On the face of it, spiders do not deserve reputations for communicability. Rather, they are popularly regarded as solitary and silent predators, who neither seek, nor are likely to obtain, partners in any gentle exchange. A moment's reflection will revise that judgment, but it is probably the first task of an introduction to offer some explanation of why the volume is thicker than one might anticipate. The events of courtship would probably be granted at once to be a matter of communication. Even the "news" which prey provides, however regretfully it does so, could be construed as communication. Indeed, this latter, very broad interpretation of the term "communication" is the one I have chosen to use in order to include material in this volume which is relevant to a consideration of mechanisms underlying communication sensu strictu. Thus, even where the research dealt with a system for prey detection, the findings of such a study could also be of interest to those seeking to understand the use of the same channel for signaling by a male spider when courting a female.

For the reader who pictures only the solitary web-builder, there will be surprises in this book, especially when communal spiders are considered. But the topic is capable of even wider expansion, so much so that in preparing this book one became convinced that to cover the problem thoroughly, it will never be thick enough. Scarcity of knowledge, rather than lack of subject matter worthy of discussion, has limited the size of the present work. In the search for knowledge, this book is a way station where we review how far we have come in order to determine where we want to go.

Invertebrates have recently become particularly interesting to neuroscientists. Chase (1979) points out that papers in invertebrate neurobiology constituted the third largest of 41 topical categories at the 1978 meeting, which represented the whole Society of Neuroscience's interest. He discusses the advantages of relatively fewer neuronal elements for identification in invertebrates, together with greater technical accessibility. This accounts for the fact that physiological descriptions of behavioral control are more complete for invertebrate models than they are for vertebrate models. If one assumes evolutionary continuity from animals to man, it follows that studies of identification of the role of particular neurons in invertebrates become relevant to the human situation. This in turn permits more enlightened speculation on the mind-body problem (see Chase, 1979).

Spiders, one of several groups making up the class Arachnida, are invertebrates which show a number of peculiarities. An example of the special body structure of spiders is shown in Figure 1.1. Spiders show a number of precoded behavior patterns, frequently called fixed action patterns. In several places in this book such behavior patterns as courtship, web-building, and feeding will be described as highly ritualized and species-specific. The neuronal substrates of such behavior probably will be elucidated one day. The following chapters review much of the present knowledge as an early step in this process. Table 1.1 lists the families of spiders containing one or more species whose names will appear in these chapters.

Why do we focus on communication? Communication is important for an animal's survival. Animals change their behavior as a consequence of the information they receive. In social animals all communal life is based on a communication network, which carries information among the individuals, letting each know what it has to do to assist in the survival of relatives and thereby insure its own best genetic interest. Communication between sexually reproducing animals is one prerequisite for their genes' survival.

There are many ways in which living beings communicate. Some of the ways are so characteristic for a species or genus that they can be used for defining the difference between that group and others. Humans are frequently distinguished from animals by the ability of our species to use language for communication. The more recent investigations of chimpanzees' ability to master and apply American Sign Language are efforts to resolve the controversy over the degree of sophistication, abstraction, and generalization which these apes can develop in this communication medium as compared to humans (Griffin, 1977, 1978; Premack and Woodruff, 1978).

Understanding communication between living beings requires insight into many different aspects of life. The organs which transmit and receive signals can be studied as to their physical appearance and particular function. The signal itself — its variation, nature, means of transmittal, and its information content — is another subject for investigation. These components cannot be understood as part of the communication process if the meaning of the message is not clarified: how it was encoded by the communicator and how it was decoded and interpreted by the receiver. Usually, observation and the measurement of the individual's behavior under specified conditions are used as methods for gaining some understanding of the content and meaning of a communication process.

The central position which communication plays in animals' lives can be deduced from the observation that studying communication leads to an understanding of the peculiarities of that animal and its conspecifics. The description of a simple experiment will illustrate the point.

A spider hangs face down in the center of its intricate orb web. A low-frequency tuning fork is struck. As soon as the vibrating prongs of the instrument touch a radius of the web, the spider turns and positions one front leg on the moving radius (Figure 1.2). This trial can be repeated over and over, and the results will nearly always be the same. Further reaction is more variable and depends on a number of circumstances: the duration of the signal, the response of the web to short jerks on the radius by the first legs, the spider's appetite, the number and character of preceding trials, and even general circumstances such as time of day, sun, wind, and rain.

What has just been described represents certain aspects of communication (broadly defined) which are characteristic of many species of spiders. The tuning fork produced a measurable signal; frequency, intensity, and variability of the signal could have been tested for the ranges in which they elicit a response. The instrument was used in place of another animal — a conspecific or prey — to test the nature, frequency, and intensity of effective signal production. The signal was transmitted through a specific channel, in this case mechanically through the silken radial thread. The channel connected the signaler with the receiver. The resulting behavior of the spider, i.e., turning in the direction of the tuning fork, provided evidence that the signal was received and decoded. The lyriform and slit organs on the legs of the spider (here Araneus diadematus) have been shown in other spiders to be sensitive to vibration-induced strains in the exoskeleton, as will be discussed by Barth. These receptors sent impulses (action potentials) along nerve fibers through the legs to the central nervous system. Here the message was decoded and translated into outgoing nerve-borne signals, which resulted in patterned muscular contractions that produced movements of the legs and body. All sections of this communication system worked together to produce an observable action- reaction sequence. As will be fully discussed in later chapters, the investigator can analyze the various parts of the system, and define the role each plays in the total process.

Beyond the general conception of communication which we have derived from this observation, it has taught us much about the animal in its living space. This particular spider, like many of its relatives, has made use of a specific signal quality, namely the vibration of the substrate on which it rests. Each type of signal, be it chemical, acoustic, visual or, as in this case, vibratory, has properties which make it practical for a specific environment. Vibration, for example, is independent of light and can be as effective at night as during the day. It is relatively independent of air currents, which can, on the other hand, carry chemicals with them. Nocturnal spiders, which build an invisible trap to catch visually orienting flies, were preadapted with a sensory system which is highly receptive, independent of vision. Many spiders have compensated for the absence of a suitable substrate over which a vibratory signal can be conducted, as well as for limitations in the distance of conduction in available substrates, by extending the perceptual range of the legs with a silken structure. It is not enough that the area of capture is enlarged; the fact of contact by the prey with the silk must be communicated. Suddenly the radiating shape of the web (Figure 1.2) takes on a new meaning for the observer: the web extends the perceptual range of the sense of vibration from about 15mm to more than 500 mm by forming a suitable substrate for the transmission of vibrations to the legs. The legs, in turn, improve reception by pulling the silk tight.

Knowledge of the organs for communication lets us understand other behaviors of the animal. During orb-web construction, the spider pulls and probes existing threads to gather information on the degree of completion, before new strands are laid (Peters, 1938; Reed, 1969). It straddles angles, apparently assessing their width and comparing them to an internal "plan" or template, which guides web construction. In the laboratory we have let the cross-spider build an orb-web in a closed box in complete darkness. Elaborate measurements carried out on the resulting webs showed no differences between these webs and those built by the same animal in partial light. No longer dependent on vision, and in darkness safe from visually searching predators, the spider builds an almost invisible web on which it will catch visually orienting prey.

Pertinent to the topic of communication is the fact that the web also plays a delicate and essential role in the spider's courtship behavior. A male may drum or pluck on the web of a female over long periods of time, until the aggressive attack of the female changes to acceptance of the male for copulation. It can be shown, by comparison of the webs of a few spider species (Risch, 1977), that the web built by the adult female is more species-specific than is the juvenile web. This observation holds for measures of size, fine structure, and shape. It raises the question of whether the specific resonance of the female web plays a role in species recognition for the "short-sighted" male. Blanke's (1973) experiments revealed reactions of males to wind which had blown across sexually mature females, suggesting that in finding the female web the male may be aided by an airborne signal, probably a chemical. This may then be followed by vibratory communication. Rarely is only one sensory modality involved in communication behavior; instead, one channel is usually predominant and others assist in one stage of communication. The roles may be reversed in the next stage.

It is not necessary to suppose that the spider has any conception of the world which she so nicely manages. In this respect, the condition bears some resemblance to the human condition. The world outside us, and the mental picture we have of it, is a product of what we can detect through our receptor organs and the subsequent analyses in the brain. We see colors and shades from which we guess at shapes and materials. We smell, feel, hear; and we use those inputs to recognize, categorize, understand objects and other living beings. Philosophers like Schopenhauer have gone so far as to describe the world as a product of our will and imagination.

Arthur Schopenhauer's principal work is the book Die Welt als Wille und Vorstellung, which appeared first in Leipzig in 1819, and was translated into English in 1883 under the title The World as Will and Idea (see ref. Schopenhauer). The second part of the title, which describes the first part of his philosophy, is of special interest here. The German word Vorstellung can also be translated as "representation, conception, mental image" (The New Cassell's Dictionary, 1958). Any of those three words appear to this writer to describe part of Schopenhauer's philosophy better than the common translation "idea." Based on Descartes, Kant, and Locke, Schopenhauer stressed the distinction between the phenomenon, or the appearance that a thing presents to the perceiving mind, and the thing as it is in itself. Through perception the mind is presumed to be aware only of the observable facts or events, i.e., of the phenomena: what lies behind them, being beyond all possible experience, is unknowable. It is impossible to dissociate conceptual thinking from the perceptual experience on which it is based. To use Schopenhauer's words (in translation): "Conceptions and abstractions which do not ultimately refer to perception [translator's italics] are like paths in the wood that end without leading out of it." In brief, our conception or understanding of the world is formed by the organs we have to perceive it; thus, we have a predominantly visual world. A very different world, mainly filled with touch and vibration signals, exists for the web-building spider. By discussing the spider's organs for communication, some of the contributors to this book try to introduce the reader to the "inner world" of the spider.

Such an argument is not intended to mean that the present author believes exclusively in the familiar "idea that there can be nothing in our intellect which has not entered it through our senses." We must assume that "every animal is born with expectations and anticipations" (Popper, 1974), which means that it possesses inborn knowledge. However, it is argued that observation of the perceptual repertoire of an animal (including the central nervous processing of signals) introduces some special understanding of the animal and its works, in our case of spiders, which cannot be gained otherwise.

(Continues...)

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Excerpted from Spider Communication by Peter N. Witt, Jerome S. Rovner. Copyright © 1982 Princeton University Press. Excerpted by permission of PRINCETON UNIVERSITY PRESS.
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Table of Contents

• FrontMatter, pg. i
• CONTENTS, pg. vii
• Chapter 1 Introduction: Communication in Spiders, pg. 3
• Chapter 2 The Significance and Complexity of Communication in Spiders, pg. 15
• Chapter 3 Spiders and Vibratory Signals: Sensory Reception and Behavioral Significance, pg. 67
• Chapter 4 Acoustic Communication and Reproductive Isolation in Spiders, pg. 123
• Chapter 5 Visual Communication in Jumping Spiders (Salticidae), pg. 161
• Chapter 6 The Behavior of Communicating in Jumping Spiders (Salticidae), pg. 213
• Chapter 7 Chemical Communication in Lycosids and Other Spiders, pg. 249
• Chapter 8 Spider Interaction Strategies: Communication vs. Coercion, pg. 281
• Chapter 9 Social Spacing Strategies in Spiders, pg. 317
• Chapter 10 Spider Foraging: Behavioral Responses to Prey, pg. 353
• Epilogue, pg. 387
• Literature Cited, pg. 393
• Taxonomic Index, pg. 433
• Subject Index, pg. 437