Editing Signalling theory (section)

==Honest signals==
[[File:2012-06-09 16-04-22 Switzerland Kanton Graubünden Sagliaz cropped.JPG|thumb|left|Eurasian jay, ''[[Garrulus glandarius]]'', gives honest signals—loud alarm calls—from its tree perch when it sees a predator.]]

{{further|Unconscious communication|Reciprocal altruism|Handicap principle|Aposematism}}

In biology, signals are traits, including structures and behaviours, that have evolved specifically because they change the behaviour of receivers in ways that benefit the signaller.{{sfn|Bradbury|Vehrenkamp|1998}} Traits or actions that benefit the receiver exclusively are called "cues". For example, when an alert bird deliberately gives a warning call to a stalking predator and the predator gives up the hunt, the sound is a "signal". But when a foraging bird inadvertently makes a rustling sound in the leaves that attracts predators and increases the risk of predation, the sound is not a signal, but a cue.{{sfn|Bradbury|Vehrenkamp|1998}}

Signalling systems are shaped by mutual interests between signallers and receivers. An alert bird such as a [[Eurasian jay]] warning off a stalking predator is communicating something useful to the predator: that it has been detected by the prey; it might as well quit wasting its time stalking this alerted prey, which it is unlikely to catch. When the predator gives up, the signaller can get back to other tasks such as feeding. Once the stalking predator is detected, the signalling prey and receiving predator thus have a mutual interest in terminating the hunt.{{sfn|Bergstrom|Lachmann|2001}}{{sfn|Getty|2002}}

Within species, mutual interests increase with kinship.{{sfn|Johnstone|1998}} Kinship is central to models of signalling between relatives, for instance when broods of nestling birds beg and compete for food from their parents.{{sfn|Godfray|1995}}{{sfn|Johnstone|1999}}

[[File:yellow-banded.poison.dart.frog.arp.jpg|thumb|upright|The [[yellow-banded poison dart frog]], ''Dendrobates leucomelas'', gives an honest signal of its toxicity to [[aposematism|warn off predators]] and reduce the frog's risk of injury.]]

The term honesty in [[animal communication]] is controversial because in non-technical usage it implies intent, to discriminate deception from honesty in human interactions.{{sfn|Getty|2002}} However, biologists use the phrase "honest signals" in a direct, statistical sense. Biological signals, like warning calls or resplendent tail feathers, are honest if they ''reliably'' convey useful information to the receiver. That is, the signal trait{{efn|Economists call what is available to the receiver "public information".}} tells the receiver about an otherwise unobservable factor.{{efn|Economists call the unobservable thing that would be of value to the receiver "private information"; biologists often call it "quality"}} Honest biological signals do not need to be perfectly informative, reducing uncertainty to zero; all they need to be useful is to be correct "on average", so that some behavioural response to the signal is advantageous, statistically, compared to the behaviour that would occur in absence of the signal.{{sfn|Johnstone|1999}} Ultimately the [[Value of information|value]] of the signalled information depends on the extent to which it allows the receiver to increase its [[Fitness (biology)|fitness]].{{sfn|Dall|Giraldeau|Olsson|McNamara|2005}}

One type of honest signal is the signalling of quality in sexually reproducing animals. In sexually reproducing animals one sex is generally the 'choosing sex' (often females) and the other the 'advertising sex' (often males). The choosing sex achieves the highest fitness by choosing the partner of the highest (genetic) quality. This quality cannot be observed directly, so the advertising sex can evolve a signal, which advertises its quality. Examples of these signals include the tail of a peacock and the colouration of male sticklebacks. Such signals only work, i.e. are reliable, if the signal is honest. The link between the quality of the advertising sex and the signal may depend on environmental stressors, with honesty increasing in more challenging environments.<ref name="Candolin 2001">{{cite journal |last1=Candolin |first1=U. |last2=Voigt |first2=H.-R. |title=No effect of a parasite on reproduction in stickleback males: a laboratory artefact? |journal=[[Parasitology]] |date=2001 |volume=122 |issue=4 |pages=457–464 |doi=10.1017/S0031182001007600|pmid=11315179 |s2cid=15544990 }}</ref>

Another type of honest signal is the [[aposematism|aposematic]] warning signal, generally visual, given by poisonous or dangerous animals such as [[wasp]]s, [[poison dart frog]]s, and [[pufferfish]]. Warning signals are honest indications of noxious prey, because conspicuousness evolves in tandem with noxiousness (a conspicuous, non-noxious organism gets eaten). Thus, the brighter and more conspicuous the organism, the more toxic it usually is.{{sfn|Maan|Cummings|2012}}{{sfn|Blount|Speed|Ruxton|Stephens|2009}} The most common and effective colours are red, yellow, black and white.{{sfn|Stevens|Ruxton|2012}}

The mathematical biologist [[John Maynard Smith]] discusses whether honest signalling must always be costly. He notes that it had been shown that "in some circumstances" a signal is reliable only if it is costly. He states that it had been assumed that parameters such as pay-offs and signalling costs were constant, but that this might be unrealistic. He states that with some restrictions, signals can be cost-free, reliable, and evolutionarily stable. However, if costs and benefits "vary uniformly over the whole range" then indeed honest signals have to be costly.{{sfn|Maynard Smith|1994}}