Chapter 16: Signal Evolutionamason/courses/AnCom/lecture5_2003.pdf · 2 BGYD45 2003:5 5...
Transcript of Chapter 16: Signal Evolutionamason/courses/AnCom/lecture5_2003.pdf · 2 BGYD45 2003:5 5...
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Chapter 16: Signal Evolution
How does the whole process get started?
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Origins
• One or both parties (sender & receiver) must initially evolve some precursor of their eventual role in communication for other reasons.
• Other party subsequently takes advantage of this preadaptation.
• Sender vs receiver preadaptations
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Sender precursors
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Sender Preadaptation Scenario1. Signal (cue) / condition association (sender code)
2. Perception of cue (signal)
3. Association of signal with condition (receiver code)
4. Association between updated information and decision rule
5. Receiver response
Receiver benefitsSender benefits
Ritualization
Tuning
Code acquisition
Preferences
Refinement
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Ritualization• Refinement of an inadvertent cue into a
signal• Likely requires fitness benefits to sender
and receiver• Involves
– simplification or reduction of number of components
– Exaggeration of remaining components– Repetition of the display– Stereotypy during repeated renditions
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Ducks
Mallard Mandarin
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Preening & Courtship
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Food advertisement and pheasant courtship displays
Males give food calls and feed mates inBobwhite quail
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Sources of visual signals• Intention movements
– Principle of antithesis• Motivational conflict
– Ambivalence– Displacement behaviour– Redirected behaviour
• Autonomic Processes• Co-option of other displays• Incidental??
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Intention movements
• Preparatory phase of some action may become ritualized into signal of intent.
• Principle of antithesis– Signals with opposite meanings (e.g.
aggression/submission) should have opposite or contrasting form
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Intention movements
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Antithetical displays
Aggressive displays usually reflectattack preparation movements
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Motivational conflict
• Animal has several motivational systems – More or less independent sources of
motivation• System which is at the highest level
dictates the current behaviour• Hydraulic model• If it’s a tie, then what happens?
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Motivational conflict in wolves
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Ambivalence
• Intention movements from both motivational systems– Mate - intruder - mate – intruder…
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Ambivalent threat displays
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Displacement behaviour
• Something else altogether– Maybe I’ll have something to eat instead
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Displacement Acts
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Redirected behaviour
• Acts relevant to one of the dominant motivational systems, but directed toward inappropriate target– Aggressive gulls tearing at grass
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Autonomic Processes
• Turning red when angry• Hair standing on end• Eyes bugging out• Etc.
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Displays from autonomic responses
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Other displays
• If a similar response is beneficial to senders, co-opt a signal from another context.
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Display co-option
Subordinate male appeasement display mimics soliciting female
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Sender precursors of auditory signals
• Visual courtship displays– Woodcock, grouse displays
• Defensive antipredator acts– rattlesnake
• Foraging movements– Mosquitoes, woodpeckers, beaver
• Respiration– High tension vocal chords = whistle,
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Jerusalem cricket
Drums but doesn’t sing.
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Giant weta:
Scrapes legs against body, has ears.
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Antithetical vocalizations
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Sources of olfactory signals
• Dietary– E.g. insects that can handle plant defensive
compounds• Reproductive precursors and products
– E.g. hormone derivatives (wild boar drool)• Defensive chemicals
– E.g. schrekstoff or ant alarm signals• De novo production
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Bark beetle mating pheromones
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Receiver bias and feature detectors
• Feature detectors are receiver refinements that improve signal detection in noise
• Feature detectors allow for invariant responses and require no learning
• Provide explanation for sign stimuli and supernormal stimuli
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Feature detectors
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Innate releasing mechanisms
Herring gull chicks use a moving red spot on bill as a sign stimulus to recognize their mother.
A yellow stick with red spots acts as a super normal stimulus.
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Receiver precursors
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Receiver preadaptation scenarios
• Models of signal evolution that propose new signals arise as a result of changes in receiver processes.
• Sensory Drive• Sensory Exploitation• Sensory Trap
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Sensory Drive• Environmental factors shape sensory system of
receiver• This imposes constraints on the effectiveness of
different possible signals• Drives signals toward certain forms that are
compatible with the environmental/sensory conditions
• Like previous model but sender has limited choice for code– In a context like mate advertisement, both can benefit
by being more obvious to one another
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Sensory driveSignal (cue) / condition association (sender code)
Perception of cue (signal)
Association of signal with condition (receiver code)
Association between updated information and decision rule
Receiver response
Receiver benefitsSender benefits
Ritualization
Tuning
Code acquisition
Preferences
Refinement
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Signalling may vary with habitat
Phylloscopus warblers: species in brighter habitats use more colour.
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Physalaemus pustulosus, the tungara frog
Sensory Exploitation
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Sensory exploitation
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Sensory Exploitation• aka pre-existing bias or hidden preferences• Pre-existing or latent preferences in receivers
are “exploited” by senders– Does not specify origins of these hidden preferences,
but some theoretical models exist• Adjust signals to match receiver bias• Origins only
– Unless receivers benefit, they will be under selection to discriminate more precisely
– “exploitation” may be a misleading term
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Water mite courtship evolution
T = male trembling mimicscopepod preyN = female net stance
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Sensory Trap• Similar to sensory exploitation, but includes
origins of female preference– Red berries hypothesis– Water mites, pretty good evidence
• Also includes importance of benefit to receiver
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Female preferences evolved prior to male swordtails
Phylogeny based on morphological data
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or do they?
Phylogeny based on mtDNA sequence data
Black = swordtailsWhite = no swordHatched = ambiguous
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How can any of this work?
• Neural network models– Trained to discriminate a given set of signals– End up particularly sensitive to a more
extreme signal (that was never part of the training)
– Could be mechanism for super-normal stimuli• Could be analagous to natural processing
mechanisms in sensory/nervous system