Discriminating customers, honest salesmen

‘Truth in advertising’ is the subject of thisrecent monograph and, if the number ofpublications [1,2] addressing this topic isany indication, honest signaling repre-sents the foremost problem for studentsof animal communication. Searcy andNowicki have done an admirable job ingathering, organizing and explaining acomplex and expanding array of theoryandexperimentalwork.Inpart,theyhaveaccomplishedthisbyfocusingexplicitlyonthereliabilityofsignals.Theauthorshave alsoselecteda restricted sampleof species groups and signals on which to concentrate:avian plumage (especially aspects that appear to be inﬂu-enced by carotenoid pigments), avian vocalization (in bothmating and parent–offspring contexts), frog calls and theappendage displays exhibited by various crustaceans.These are arguably those phenomena that have beenprobed most deeply, and the various studies provide theauthors with the material needed to evaluate the basichypotheses and their many corollaries. Nonetheless, onecould ask whether observations from a more extensive setof animals would have altered any conclusions.The Evolution of Animal Communication begins bylaying out the basic dilemma: if signals are not reliableindications of the state, ability or intention of the trans-mitter, receivers ought not to attend to them and, becausesignals are likely to bear some cost in development and/orproduction, unattended signals should eventually disap-pear. Thus, a mechanism that ensures honest indication isexpected, except in those cases where signalers and recei-vers have largely overlapping interests. In this situation,the mechanism is intrinsic: it is in the interest of thetransmitter to broadcast signals that are by and largetruthful. But, elsewhere, it is generally assumed thatsignals are costly and that inferior individuals (or thosewith inferior needs) cannot (or should not) bear the eco-nomic cost that would be required to send out a falseadvertisement. With this basic logic, which has been mod-iﬁed by many speciﬁcations to suit various social affairs,thequestionbecomesasearchformechanismsthatensurethe differential cost. Consequently, much attention is paidto those signals that appear to be honest but do not comewith any recognizable cost (e.g. avian badges) and to thosecases that involve some measure of deception.The authors expand upon this framework in three chap-ters that deal with communication in which the expectedlevel of conﬂict between the participants is successivelygreater. Each begins with a presentation of the relevanttheory,followedbytreatmentoftheempiricalliteratureandan assessment of theory as revealed by experimental ﬁnd-ings.Recognizingtherecentawarenessthatcommunicationoften occurs among networks [3], as well as within pairs, ofindividuals, a fourth chapter explores the reliability ofsignals as perceived by third parties and other audiences.I found the writing to be unusually clear and well-balancedthroughout. The authors rely on text and simple ﬁgures totranslate some intricate theory into cogent arguments andhypotheses with deﬁnite predictions. That said, several‘mathematics boxes’ in addition to the two included mighthave strengthened some parts. The reporting of the litera-tureisquitefairbutnottotheexclusionoftheauthors’(well-informed) opinions where deemed necessary. Appeals forfuture work in crucial areas are made, and there is aninteresting section on the authors’ novel work on the relia-bility factor in the dialects of songbirds.After reading The Evolution of Animal Communication,I felt that my appreciation and understanding of the sub-ject was improved. But I was also left with the feeling,particularly following the section on networks, that beha-vioral ecologists are masters of generating hypotheses anorder of magnitude faster than they can ever be tested.Here, part of the imbalance might reﬂect what we do notyet know about the perception and cognition side of com-munication in most species, and the extent to which thesefactors might constrain reliability. Another issue nottouched upon is the potential impact of unpredictableenvironmental variation, coupled with genotype x envir-onment interactions, on signal reliability [4]: What is thevalueofsignalsthatindicatereliablywhenthetransmitterhasdevelopedinoneplaceandtimebutnotinanother,andwhat sort of signals might be resistant to this dilemma?That said, The Evolution of Animal Communication is a‘must read’ for any student of behavioral ecology. It isconcise but thorough, and represents our clearest descrip-tion of a complex area that has seen several major shifts intheory over the past 30 years.