Lecture 9 T Flashcards
How do animals communicate?
Through signals and cues!
Both are a feature of one individual (the sender) that modifies the behaviour of another individual (the receiver)
What are cues?
The receiver uses some feature of the sender to guide their behaviour, but this feature has not evolved for this purpose
Give an example of a cue
Carbon dioxide as a cue to mosquitoes.
Animals don’t breath out carbon dioxide to attract mosquitoes
What are signals?
Signals have evolved to allow the sender to guide the behaviour of the receiver
Receivers must also have evolved response to signals- either before or after the evolution of signal
The signal must benefit the receivers or they would ignore it
Give an example of a signal
Body weight (cue) vs web vibrating (signal) as indicators fighting ability in funnel-web spiders
How must signals evolve?
A signal must have evolved independently of the feature about which it is conveying
What keeps signals honest?
3 hypothetical reasons
The signal is costly
The signal is constrained
Signaller and receiver have a shared (or common) interest in signal honesty
Give an example of a constrained signal
The peacocks train may be constrained by the size of the male-only large, high-quality males can carry extra eyespots
It would be reliable signal because it cannot be faked - index
What is an index?
An index is signal whose intensity is causally related to the quality being signalled and which cannot be faked
Why are signals costly?
Poor quality makes could make more eyespots but it would be prohibitively costly for them to do so - e.g trade spots between signal and immune function
If the signal was faked, males would experience low mating success for other reasons (e.g. Health)- handicap
What is a handicap?
A handicap is a signal whose reliability is ensured because it is costly to produce or has costly consequences
Why does common interest drive honest signalling?
E.g. Genetically compatible mates may raise healthier offspring
In such cases, a fake signal would not benefit signaller or receiver
Give an example of indices in mammals
Red deer stags compete for females
Reproductive success depends on fighting ability- but fighting is costly (20-30% of males are permanently injured)
Costs minimised by assessment of fighting potential- indices (height, vocalising lower frequencies) can’t be faked
Give an example of indices in amphibians
Croak of the common toad also provides an index of size and fighting ability - lower = bigger
Larger males more successful at dislodging smaller males
Why can’t indices be faked?
Occasionally changes (e.g. Larynx structure mean that deeper sounds can be produced)
This would allow males to exaggerate their signal, but make it unreliable
The new structure would quickly spread to fixation, and become a index again
