Design features of animal signals

Sinauer Associates, 1998. £32.95 hbk (xiii + 882 pages)ISBN 0 87893 100 7Fine wines, cicadas, truffles. These are the kinds of things that require time to mature, time to become specialty items with unique signatures. Bradbury and Vehrencamp’s Principles of Animal Communication (hereafeter PAC) joins this illustrious list. PAC has been incubating for 25 years. It represents the culmination of the authors’ teaching and research efforts, and a thoughtful synthesis of the voluminous literature on communication in animals. The breadth of taxonomic groups covered is astonishing.The book is dedicated to three of the pioneers of animal communication who, together, covered most of the major animal groups—Robert Capranica for frogs, Donald Griffin for bats, beavers and bees, and Peter Marler for birds and primates. And the comparative approach is crucial, for in this book, Bradbury and Vehrencamp do what no one has really done before. They use the power of Darwin’s brainchild to illuminate biological principles of design, principles that show the workings of natural selection to sculpt adaptations. And what adaptations could be more important than those related to communication? Communicative signals provide the functional glue for maintaining species integrity, for attracting mates, detecting predators, manipulating competitors, mediating parent–offspring interactions and facilitating cooperative interactions.PAC is divided into three parts. Part 1 (on production, transmission and reception of signals) deals with the diversity of signaling modalities in the animal kingdom, and the mechanisms that allow for their transmission and reception in different environments. Thus, we learn about the physical acoustics underlying vocal signaling, the problems of spatial discrimination and temporal resolution relevant to visual displays, the biochemistry of pheromonal signals, and the detection of electric fields in different transmission media; there is little mention of seismic signaling, but this has only recently gained the attention of biologists1xNarins, P.M. BioScience. 1990; 40: 268–274CrossrefSee all References, 2xNarins, P.M. et al. Brain Res. Bull. 1997; 44: 641–646Crossref | PubMed | Scopus (52)See all References.The material covered in Part 1 is heavy, demanding an integration of fundamental principles and theories from physics, mathematics and chemistry. Bradbury and Vehrencamp have done an admirable job in making this material not only comprehensible, but interesting. Moreover, they raise (implicitly) the point that those who jump into animal communication with a singular interest in adaptation and functional design must acquire an appreciation of the biomechanical and ecological constraints imposed on the structure and, consequently, efficiency of a signal. Students of animal communication should also appreciate constraints at the neural level, a problem that is not covered in PAC, but as the authors point out, has been reviewed in other texts3xThe Evolution of Communication. Hauser, M.D. See all References, 4xSee all References, 5xThe Evolutionary Biology of Hearing. Webster, D.B., Fay, R.F., and Popper, A.N. CrossrefSee all References.Part 2 (on optimizing information transfer) takes as its starting point the view that communication is about the transmission of information, at least in some form. The bulk of this section represents an attempt to integrate the evolutionary biologist’s fondness for economic analyses with the psychophysical and statistical insights from information theory, and in particular, signal detection analysis and Bayesian probabilities. The authors generate many creative insights, and they argue to great effect that there are tasty analytical tools available for quantitatively assessing the causal effect of a signal on a perceiver’s response (e.g. receiver operating curves, Bayesian updating procedures), as well as for determining such aspects of a communication system as its repertoire size, the units of analysis (both from the researchers perspective as well as the signalers and receivers), and the costs and benefits of signal transmission and reception.Although I am completely sympathetic to some of the tools they suggest and recommend, I am somewhat skeptical that such tools will be of general use. For example, many of the statistical and signal detection techniques will be difficult to apply because the experimental tools required to extract the relevant data are either insufficient, or cannot be implemented on all species and in all modalities. Along these lines, the authors correctly note that we know relatively little about signaling in the visual modality because the experimental and analytical tools have yet to be developed or applied in a serious fashion; they do, however, neglect the potential revolutionary developments in video technology that have allowed researchers to assess the mechanisms of courtship in jumping spiders6xClark, D.L. and Uetz, G.W. Anim. Behav. 1990; 40: 884–890Crossref | Scopus (92)See all References, 7xClark, D.L. and Uetz, G.W. Anim. Behav. 1992; 43: 247–254Crossref | Scopus (85)See all References, species recognition in lizards8xMacedonia, J.M., Evans, C.S., and Losos, J.B. Anim. Behav. 1994; 47: 1220–1223Crossref | Scopus (50)See all References8 and predator detection in domestic chickens9xEvans, C.S. and Marler, P. Anim. Behav. 1991; 41: 17–26Crossref | Scopus (114)See all References9.Part 3 (on game theory and signaling strategies) begins with the application of game theory to the problem of animal communication and the stability of signaling strategies over evolutionary time. This not only represents a good review of the literature, but an excellent introduction to the logic of game theory, its underlying assumptions and applications. Having raised such problems as alternative strategies, frequency dependence and evolutionary stability, Bradbury and Vehrencamp go on to discuss the topics of honesty and conflict resolution, followed by an analysis of five communicative contexts: territoriality, mating, social interaction, environmental conditions (e.g. predators, food) and self (i.e. echolocation in bats and cetaceans).In general, I found this section of the book thoroughly enjoyable, and filled with both fascinating examples, and insightful intuition into general principles of signal design. My only disappointment was that the authors failed to capture some of the controversy currently emerging over the stability of Tit-For-Tat strategies, as well as conflict over the interpretation of many putative cases of reciprocal altruism (see, for example, the recent reviews by Dugatkin10xCooperation Among Animals: An Evolutionary Perspective. Dugatkin, L.A. See all References10 and Sober and Wilson11xUnto Others. Sober, E. and Wilson, D.S. See all References11).Bradbury and Vehrencamp say that the book is aimed at undergraduates, as well as graduate students. I think this is the only level at which the book fails. I have given sections of the book to several undergraduates and they have struggled. Granted, the math, physics and chemistry are relatively elementary, but not for a lot of students who nonetheless have a passion for, and working knowledge of biology. Consequently, using PAC to teach undergraduates will require an instructor that cannot only do the math, but who can teach it with ease. That said, Bradbury and Vehrencamp should be applauded for providing the field of animal behavior with an incredible synthesis. No one interested in animals should be allowed to have this volume missing from their libraries. It will, for a long time to come, provide a guiding light. Bravo!