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Animal Signalling and Communication Purposes of Signals Signal Components Tactical Components 2. Sexual ritual or calling behavior between males Purposes of Signals and females Tungara Frogs Fireflies Animal Signalling and 1. recognition of species, individuals, neighbors, castes (social insects), kin, or demes 3. Establishing territories and/or social status Communication •Bird-song differences between species: are they Red deer, red-winged blackbirds adaptive? •Allopatric Speciation 4. Alarm calling •Hybridization zones Ground squirrels •If hybridization decreases fitness, we’d expect Outline: Great tits and other birds subject to raptor predation greater song differentiation in areas of closely- 1. Purposes and variety of Convergent evolution in “seet” calls related species overlap. signals •Gill and Murray (1972): Compared bird songs of 2. Signals in evolutionary context golden-winged and blue-winged warbler in areas of species 5. Information in groups of foragers Tactical components overlap and non-overlap Honey-bee example. The Sensory exploitation “Waggle Dance” Unintended receivers •Songs were less 3. Evolutionary thought on signalling varied in areas of Number of waggles gives •Strategic components overlap, perhaps info re: distance to food •Honest and deceptive signals because it was •Zahavi’s handicap principle adaptive to be more Direction of the straight- 4. Specific examples in territorial behavior specific. run gives info regarding •But this is a lone the direction toward a study amongst Golden-winged warbler food source. many that suggest bird song is not so important for species recognition. Tactical Components 6. Parental care: offspring/parent recognition Signal Components “Getting the message across” Studholme (1994): Example from Johnstone (1997): Anoline lizards Fiordland penguins Tactical Components: and the “assertion display” versus the “challenge Offspring orient to and Features of a signal which are concerned display” respond to their parent’s with how easy it is for the signaller to calls more than other calls. (But parents seem transmit it, for the receiver to receive it and less responsive to their discriminate it from other signals. particular offspring’s call.) Strategic Components: The assertion display is not Properties of a signal that are concerned sent out to anyone in parti- with what good they do to the signaller, i.e. cular. But it “ought” to be how does the signaller benefit from emitting noticed by some other lizard. the signal. Conveying Hunger levels: •Common features of signals ensuring their appropriate reception: Adult birds bringing food back Both have been viewed from an adaptationist 1. Conspicuousness for nestlings. The hungrier nestlings perspective. 2. Stereotypy analogy to electronic signal transmission could scream louder. 3. Redundancy } 4. Alerting components Tactical Components and the Back to the Methodology Zone for a moment: The Nasty Statistical Issue: It is important to know if the observed relationship Environment The Comparative Method between the two variables in statistically significant. Signals’ conspicuousness seems to have evolved with However a simple linear regression (put a least- respect to the environmental background. •Definition: squares-fit line through the data and then test to see •Marchetti (1993): Plumage patterns of congeneric Quite often, the relationship between two traits, if the slope of the line is significantly different from warblers. Those living in low light environments had OR the relationship between an environmental zero) is invalid because it assumes that all the brighter plumage. characteristic and an organismal trait will be observations are independent. •Wiley (1991): Comparison of song-birds in North explored by comparison of the traits and American habitats. environments across species (or other taxa). But in the comparative method, the different points •Rated sonograms of birdsongs for The goal is to demonstrate a significant are not independent. They are related by their •period of repeat of elements correlation between the two traits in question, or common phylogenetic history. Consider: •buzzes between the environmental conditions and the trait. This, then, might be taken as evidence of •side-bands oo o adaptation. This process is called the o o •Categories for habitat type (i.e. grassland versus o forest, etc) Comparative Method. x xx x •Songs from birds in open habitat had more •Example: Length of Rep. El. reveberation-degradable features than songs from Studying, for example, the length of a repeated Env. Reverb forest habitats. element in bird songs versus the amount of x reverberation from the environment x x x xx each x represents a x x x different species o x o x xx x o Some Sonograms of different birdsongs Length of Rep. El. o Env. Reverb o If the X’s and O’s are more closely related to one another, Tactical Components and the Tactical Components and evolutionarily, then the observations in the cluster of X’s and the cluster of O’s are not independent of one another. “Audience” Unintended Audiences “Color blind organisms should not have colorful A simple linear regression will treat each point (species) as displays or signals.” Any time an animal is signalling, the message if it were an independent observation. may get picked up by an unintended receiver The Result: too much statistical significance inferred. Sensory Exploitation: (for example a predator). When signalling behavior evolves to take advantage of In reality, bird species of the “x” cluster may have all pre-existing sensory biases. Two types of alarm calls in great tits: inherited a mutation that shortens the length of song Proctor (1991): male water mites Mobbing alarm call: loud indiscreet signal to elements, and they may live in less reverberative “tremble” at a similar frequency to others to mob and molest a perched hawk. environments, but the two may not be related. prey. The females are acutely sens- itive to this (being part of their for- “Seet” alarm call: short, high-pitched, discrete There are methods to try to correct for the non- aging behavior repertoire). alarm call given to warn others of a flying hawk. independence between closely related species (for example Felsenstein (1985)). The female grabs at the The frequency of the seet call is high enough that These are what Johnstone is referring to when he uses male who somehow con- hawks cannot hear it very well, but it is well within phrases like “incorporating various measures to control tends with the female’s the range that great tits can hear well. fro the effects of phylogeny.” mouth parts, and is able to effectively mate with (Studies with hawk orientation to recorded seet her. calls.) Was this sensory exploita- tion? (Proctor 1992) and phylogenies. The Evolution of Strategic Signalling and Conflict of Honest Signals Interest Components of Signals An honest signal is one which reflects the true state of Signaller and Receiver don’t always stand to benefit in the sender by virtue of physical necessity Traditional Ethological View (Pre-1970’s) the same way •Signals were there to “facilitate and coordinate Examples: social interactions by making information available Examples: Hill and Montgemorie (1994): Correlation between to be shared.” Displays of territory owners coloration and nutritional condition of male house •Reasonable for cooperative signaling--- finches •When both the signaller and the receiver In some species males seek matings with as many benefit females as possible while females seek to mate with •Deceit was not commonly considered, even the “most fit” males though it was well-known on an inter-specific level, i.e. Batesian mimicry: Early 1970’s. Maynard Smith and game theory for signalling---without appropriate controls deceit should abound and signals should evolve to become meaningless. Since signals are not all meaningless, something has Clutton-Brock and red deer roaring contests maintained their honesty or utility. What? Two main (and related) types of explanation: Also, frog-croaking tone. Small frogs •“Honest Signals” are unable to croak at the lowest freqs. •Handicap Principle Main point = direct link between the ability to generate the Viceroy Butterfly Monarch Butterfly These reflect other evolutionary pressures that may be signal and the physical condition or foraging ability (taken Basilarchia archipus Danaus plexipus acting on signalling behavior to be a surrogate for fitness) of the signaller Another way (in theory) to curtail deceit Handicap Principle At the heart of the Handicap Principle are (Zahavi 1975 and later) Condition-Dependent Cost or •Similar to the Honest Signal notion, but here the link Benefits between condition and the ability to generate the signal is The signal/handicap must cost more for the “low-quality” not so clear. individual than the “high-quality” individual •Rather, deceit is discouraged because one must have high fitness in order to overcome the handicap of the signal. Conceptually/Graphically: •Example: Andersson (1982): Male Widowbirds in central Costs to africa. The “signal” is the long tail. Low Qual. Benefit of •Females have a preference for males with long tails Indiv. the signal •The tails don’t confer a fitness advantage to the males- --if anything they are a handicap. Male Widowbird Costs to Hi Qual. Indiv. Costs and Benefits Notion of the handicap principle Signal Intensity echoes Veblen (1899): The Theory of the Leisure Class, and his idea of This has made actual testing of the Handicap “conspicuous Principle very difficult. Almost no studies consumption” have managed to quantify condition-dependent costs..
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