Signal Honesty

• Definitions and history

• Alternative models– Agonistic displays– Courtship– Begging

• Explanations for deceit

Honesty vs cheating

• Sender deceives receiver– emits false signal

• bluff - amplifier

• mimic

– withholds signal, e.g. alarm

• Receiver exploits sender

Signal honesty in perspective

• Classic ethology– all signals are honest because source of signal is linked

to motivation

• Game theory (Krebs and Davies 1978)– Arms race occurs between deceitful signalers and

discriminating receivers

• Signals as handicaps (Zahavi 1977; Grafen 1990)– Receivers only attend to costly signals, which can only

be produced by honest senders

Honesty requires costly signals

Goldfinch displays predict outcome

Grafen’s handicap signaling model• Signalling is costly to males• Cost to high quality males is less than to low quality males• High quality males have higher probability of mating• Low quality males never do better than high quality males

Male damselfish display rate correlates with paternal care

House finches signal with carotenoids

Carotenoids cannot besynthesized, so their Display by males provides an honest measure of a male’s foraging ability

Status badges signal dominance

Honesty is insured if largebadges are challenged andthere is a cost of beingaggressive (testosterone)

Begging

• Sender tries to persuade receiver to provide aid• Receivers do not benefit unless

– Share genes in common with sender (kin selection)

– Repay the favor later (reciprocity)

• Honest senders only beg when in need• Signal production must be costly (perhaps by

attracting predators) to insure honesty

Sir Philip Sydney Game• Wounded officer has to choose between donating his last water to a begging

wounded soldier or keep it for himself• Sender strategies

– Only beg when in need– Always beg regardless of need– Never beg

• Receiver strategies– Only give to senders when they beg– Always give to senders– Never give to senders

• Two ESSs, assuming some relatedness– Sender never begs and receiver ignores– Sender only begs when in need, and receiver only gives in response to begging, requires

a cost to begging, costs covary with r

Evolutionary games on honesty

Examples of deceit

• Foraging birds give alarm calls to scare competitors away from food (Møller)

• Rhesus macaques will withhold food calls when food is discovered unless relatives are nearby

• Mantis shrimp will threaten after molting when vulnerable (Adams and Caldwell)

Bluffing by mantis shrimp

Flee, threaten, do nothing

Threat display.Newly moltedanimals can beseverely injured

Responsesof newlymoltedresidents

threaten, do nothing

Explanations for deceit

• Perceptual error by receivers allows cheaters to escape detection

• Evolving signaling systems are not at the ESS

• A single type of receiver may have to deal with multiple senders

Consequences of player error

• Adding error to games insures that all strategies are tested and thereby improves stability

• Senders need not be perfectly honest. If receiver error is 10%, why should a male signal 10% more than another male? – Senders should increment in steps according to

magnitude of error. – Provides explanation for stereotypy

Receiver error in handicap models

Multiple senders

• What if there are two beggars: one honest and one that always begs regardless of need?

• ESS is for receivers to respond to begging as long as honest beggars are closely related to receivers or honest beggars pay a higher cost than constant beggars, if they are sufficiently common

• Provides explanation for mantis shrimp, etc.

Sensory exploitation and neural networks

• Senders that exploit receiver biases are sending dishonest signals. Is this stable?

• Neural network models can be used to examine this issue.

• If senders and receivers evolve, honesty can emerge.

Neural network model

• Use 3 layer neural net to produce and receive signal

• Senders vary in quality and produce multidimensional signals

• Receivers locating highest quality senders have highest fitness and leave more progeny

• Compared outcomes with and without signal costs

Outcome

• In absence of costs, sender fitness rises at expense of receiver

• When signaling is differentially costly, receiver fitness can rise proportional to number of signals used.

• Periods of exploitation recur and are followed by honest signalling