Animal Communication

III. Function, b. Honesty in Advertising

ABGG Core Class Fall 2012 Functional Issues: Part 2 - Honesty

III. Function, b. Honesty in Advertising We have a conflict of interest with advertisers: they want us to buy their product, we want to buy the best product

III. Function, b. Honesty in Advertising Early ethological approach: Because signals evolve from intentions, preparatory movements, physiological precursors, etc… they reliably predict what sender will do next because sender can t help it (they are constrained to be honest). Often ignored conflict entirely, and viewed communication as an altruistic exchange of information Dawkins/Krebs arms race and early game models: Senders should try to trick, mislead, and manipulate receivers into giving responses benefiting sender, and receivers should become mind-readers trying to discount false signals Zahavi Handicaps: Receivers only pay attention to signals that impose a cost (handicap) on senders, which makes it costly to send dishonest or exaggerated signals

III. Function, b. Honesty in Advertising, 2. Current Thinking There are several dozen game-theoretic models of communication when there is a conflict of interest between the sender and receiver, each depicting a different signaling context Common theme: There must be some type of cost or constraint imposed on senders to guarantee honesty, but this cost is different for each model or context We ll discuss 3 categories of costs in communication: A. Necessary costs B. Incidental costs C. Constraints Both senders and receiver may pay these costs, but it is the cost to the senders which we use to categorize the signals. Costs to receivers are also important, because they select for mind-readers who only respond to honest signals.

Animal Communication, Part 2: Function!

III. Function, b. Honesty in Advertising, 1. Costs A. Necessary Costs: Costs paid up front, do not depend on receiver response, includes: • 

Prior investment by sender in special structures, coloration, organs, brain circuitry, etc.

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Immediate costs sustained by sender while communicating such as time lost, energetic expenditure, and predation risk

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Receivers also pay some necessary costs (assessment costs, possible brain and sensory costs, etc.), which favors receivers who only pay attention to honest signals (i.e. mind-readers ).

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III. Function, b. Honesty in Advertising, 1. Costs B. Incidental Costs: Decreases in magnitude of payoffs to either the sender or receiver; does depend on receiver response • 

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Costs to the sender: if the receiver punishes the sender for sending the signal (e.g. badges of status), this selects for honest signals. Receivers can also pay incidental costs: If sender deceives the receiver into acting against the receiver s interests (sender deceit, bluff, exaggeration, withholding information). These costs select for receivers who only pay attention to honest signals (i.e. mind-readers ).

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III. Function, b. Honesty in Advertising, 1. Costs C. Constraints: limits on communication imposed by environment, phylogenetic history and physics Examples: Frequency and amplitude are limited by body size, brain size limits learning of songs, etc. These aren t always costly to signalers, but they prevent cheating because overcoming the constraints (if that s even possible), would require costs too large to bear

III. Function, b. Honesty in Advertising, 3. Types of Signals Type of cost affects the signal form, i.e. whether the signal is arbitrary or linked to the signal message (e.g. I am big ) Approach: classify and name signals by the type of cost that guarantees honesty Doing so, we end up with three types of signals:

A.  Quality handicap signals B.  Index signals

Indicator traits

C.  Costly Conventional signals Seismic courtship in Jumping spiders (Elias, et al. 2003)

Note: this is yet another area with many different terms and frameworks!

III. Function, b. Honesty in Advertising, 3. Types of Signals, A. Quality Handicaps

III. Function, b. Honesty in Advertising, 3. Types of Signals, A. Quality Handicaps

Zahavi (1975, 1977) proposed that signals need costs to maintain honesty, and that we should see that animals pay for their ornaments with fitness costs (e.g. they use up some of what they re advertising) Idea not given much credence until 1990, when Grafen created a plausible game theory model showing that it works. Recent work by Getty makes the story much more complicated! Maynard Smith and Harper (1995) discuss how there is a minimum efficacy cost that must be paid to send the signal; handicap signals are Cost-added signals , where there is extra cost paid beyond efficacy cost to ensure honesty (this is often forgotten in measures of handicap costs)

Animal Communication, Part 2: Function!

Cost: necessary costs (signal production costs, predation) Key feature: Poor quality individuals pay a higher cost to produce a given level or intensity of display compared to high quality individuals (condition-dependent handicap model) Signal form: graded and linked to that aspect of quality that the receiver wants to know (signal "uses up" the quality feature of interest). Information: Condition, health, vigor, fighting ability Contexts: mate attraction, some agonistic interactions

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III. Function, b. Honesty in Advertising, 3. Types of Signals, A. Quality Handicaps

III. Function, b. Honesty in Advertising, 3. Types of Signals, A. Quality Handicaps

Grafen 1990 model of mate quality asymmetric continuous-strategy scramble

Cost or

Female mate preference

High-quality male

Benefit

Display intensity

Nesting females

Low-quality male

Widowbirds (Malte Andersson, 1982)

Assumptions: 1.  Displaying is costly, reducing survival of displayer 2.  High-quality male pays lower cost than low-quality male Table 2. Final terms in a general linear model for mean wave height the experimental treatment. The to original model in3. afterFemales more likely mate cluded male claw length and all two-way and three-way interacwith high-investing male tions between terms (see text). 4.  Female preference for given Source df F P display level is not different for Treatment 1,22 13.93 0.001 high and low quality males Mean height before 1,22 206.27