Signals Flashcards
What is an animal signal?
Information of one animal is being conveyed to another, the receiver.
Example: all sounds except echo location are signals
- attract: make cricket call female to burrow
- repel: make Robbin repels others from territory
- change physiology: male canary song causes mates ovaries to ripen
Aimed at own species or other
May have unintended effects
Example: cricket song is designed to call females but also calls parasitic flies and is eventually fatal - is this not then a signal to the flies? No as it is a consequence.
Has lead to evolution of morphological organs - crests and voice boxes
‘economy of effort’
This is the idea that signals are more efficient as they have their effect without any direct physical force
Example: Toxic frog
However, this cannot explain the evolution of signals as signals can be very costly and are not necesarily muted and subdued (e.g. exaggerated colour, plumage, sexual display)
- used in classical view which looks at signal design where signaller and receiver have common interest -> trying to convey signal efficiently
Example: bowerbird extended sexual display
Signals must have specially evolved for communication
Animal behavior may appear to be a signal but they are only signals when they have evolved for communication.
Example: Paler Bucephala moth
- Camoufalged as a twig for defence
- Predators have learnt to detect this camouflage it provides the predator with informations
- This is not a signal
Arms race due to mind reading
- so surely this evolutionary cause of signals is not a signal
- the receiver is using a signal to predict future of signaller, the signal has not evolved to convert information.
Honest vs cheating signals
Signals can be honest or cheating
Individuals are part of a ‘signalling system’ which is stable when the majority of signals are honest so it pays for the receiver to belive the signal.
Example: stomatopod shrimp
- Shrimps use their claw as a myriad signal
- When they are malting the claw is a dishonest signal
- However, the signal is honest more than it is dishonest due to limited frequency of malting
The classical view for the evolution of the design of signals
Signals are designed to overcome problems with signal detection and recognition. Signal and receivers have common interests and signals are evolved to be more efficient.
Problems:
- back ground noise
- Distinguishing signals from each other
- Signal degredation
- Correct recognition and reponse
Solutions
- Conspicuitiveness (distinctive)/ stereotype
-> The distinctiveness allows receivers to tell apart signals (Wattler birds)
-> The stereotypes/ typical intensity enable receivers to use variations in signals to make decisions (Stotting in Gazelles)
- repetitive and redundant (e.g. bird song)
Initially the signal likely evolved from a movement that formally had no function
- e.g. preening or feather settling in birds
Signal may be derived from another signal
- crouching of songbird females in courtship comes from juvenile begging
Unlikely that mutant derived signal (entirely new movement)
Movement then becomes ritualised to become a signal (e.g. reprieve and stereotype)
The modern approach (Dawkins and Krebs)
Animals and signals evolved not to transit information to receivers but to manipulate them to react in ways beneficial to the signaller.
Evidence of this are supernormal stimuli which manipulate receivers to act in a certain way
-> e.g. Ringed plovers preferred artificial eggs to their own eggs if they had exaggerated markings
-> e.g. bee orchids present supernormal stimulus of a female bee and male collects pollen while trying to copulate. (Manipulation)
Evidence:
- stickle back respond aggressively to red mail van passing window
Theory claims there is no difference between sea otter using a stone to crush shellfish and using female to raise young -> uses force to manipulate stone and signal to manipulate female
-> natural selection favours behaviours signalling to female
How do signals evolve under this modern view of evolution
-The nature of co-evolution depends on whether the vinctom (either the one having its mind read or the one being manipulated) is willing or not willing).
Arms race via manipulation
-> Signals started evolution by triggering a supernormal response in the receiver
-> Receiver evolves reduced sensitivity
-> Signaller escalates signal and there is an arms race
Non-willing
-> Leads to escalation of signals
-> Bee and orchid, Cuckoo, sexual selection
Willing
-> if there is a benefit to the one being manipulated they are less likely to evolve to be less sensitive.
This suggests that conspicuous, stereotypes, exaggerated signals are not mechanisms for efficient information transfer, they are instead over-the-top instruments of manipulation (result of antagonistic arms race) -> Handicap is required to stop dishonest exageration
Arms race via mind reading
-> Receiver detects cues that predict the future of an emitter
-> The emitter (signaller), reduces the conspicuousness of such que (more cryptic)
-> Receiver gets more sensitive to the cues
-> Arms race for stealth and concealment
Unwilling victim
-> Signal gets more and more concealed, and animal gets more sensitive to fine clues
-> Example: clever horse that pored ground until he got to the right answer. Turns out was looking at the owner for a signal -> owner made signal more concealed and horse got more sensitive.
Willing victim and fitness interests align
- It may benefit the emitter to have its mind read
- This means signal may not become more concealed.
- Example: female read signals that mate is aggressive or wanting to mate. Benefits mate as avoids him having to be aggressive or kill a female (may mate with in future)
- For example: eye contact with prey showing you have seen them
Cooperative breeding: Conspirational whispers (e.g. the waggle dance)
-> may pay to make signal less obvious as less expensive (e.g. attract predators)
Mind reading often predisposes manipulation
Zahavis problem with Dawkin’s and Kreb’s view
Zahavis reasoned that if conflicts of interest lead to signals that manipulate the fitness interest of the receiver then how do honest signals evolve and persist? Surely would make sense to produce dishonest signals to manipulate the receiver.
Solution: Handicaps
1) impossible to cheat: The signal has a physical connection to the quantity being signalled about (e.g. depth of frogs croak is restrained by their size)
Example: signal and reward may be the same. Plant produces nectar as reward to pollinator, intensity of smell attract the pollinator (signal) cannot cheat as intensity depends on nectar production. But flower may produce smells to mimic nectar.
Example: growth of petals has large energetic cost so rarely used for cheating
2) Not worth cheating: The cost of signals is proportional to the quality of the individuals so cost-benefit analyses reveal optimum for low-quality individuals is less than for high-quality individuals. (e.g. roaring in red deer stags taxes the thoracic muscles needed for fighting and there is a greater cost for low-quality individuals)
Selection for honest signals favours physically constrained, expensive signals.
A more integrated view: two-component signal design.
Have signals evolved to be efficient or costly? Manipulative or informative?
When considering how signals have evolved it can be helpful to consider that they have evolved for two different functions.
Signal content: This considers how a signal is designed to contain a particular message (e.g. handicaps leading to hoest signals)
Signal efficacy: This considers how signals have evolved to get the message across (detectable, distinctive and recognisable)
-> They have evolved to the landscape of receiver psychology
Example of the integrated view of evolution
Head bobbing and dewlap extension of Anolis lizards
Stage 1: This has evolved for efficacy
- Constant dewlap and exaggerated head bobbing to catch attention
Stage 2: This has evolved to show signal content
- Dewlab extension becomes active and head bobbing is less jerky
In most signal both functions are merged together (e.g. red dear roar is both detectable and honest as it is costly)
Example: plumage in manican
- high levels of sexual selection
- efficacy: maximise contrast against back ground
- mechanisms: different colours are produced by different mechanisms which vary in expense
- potential trade off as more expensive colours may not be more contrasting
Overview
The evolution of animal signals
Classical view: Signal design was a series of solutions to the problem of signal detection and recognition
- Consciousness
- Repetitive/ redundant
- Distinctive/ stereotype
- Typical intensity
The modern approach: animals and signals evolved not to transmit information to receivers but to manipulate them to react in ways beneficial to the signaller
- Arms race via manipulation
- Arms race via mindreading
But how can honest signals continue under this model as surely dishonest signals will evolve if signallers are trying to manipulate the receiver?
Handicaps
- Impossible to cheat: Signal selection would favour characters that had some necessary physical connection to the quality being signalled about. (not possible to display a dishonest signal)
- Not worth cheating: Even if it is possible to display a dishonest signal it may not pay do so due to difference between costs and benefits.
-> To produce an exaggerated signal would be more costly than the benefits gained.
A more integrated view of signal design
Two-component design:
Signal ‘content’
- How is the signal designed to contain a particular message?
- The signal may have a handicap.
Signal ‘efficacy’
- How a signal is designed to get the message across
- Detectability, Discriminability, memorability (receiver psychology)
Example: Head bobbing and dewlap extension in Anolis lizards
- Efficacy: First part of signal
- Content: second section of signal
