Week 6: Evolution of communication Flashcards
Acoustic communication in crickets
signaler (male) — information –> receiver (female)
As a result of acoustic communication, both female fitness and male fitness increase
Communication is adaptive for both male and female crickets.
Not all male crickets are singing in the field
Male mating tactics in crickets
- calling tactic:
- produce calling songs
- defend calling territory
- high reproductive success
but
- spend energy to produce sound
- may be parasitised by illegitimate receivers - Satellite tactic:
- sneak in a calling male
- remain silent
- try to intercept a female
but
- low reproductive success
Parasitic fly
Ormia ochracea:
A female fly is attracted by the song of the male cricket and deposits larvae on or around him.
The larvae quickly burrow into the host and emerge about 7 – 10 days later, killing the host.
The parasitic flies are illegitimate receivers to calling males
Life stages of crickets and life cycle
egg –> juvenile (nymph) –> adult (fully developed wings and fertile)
most cricket species in Korea (one generation per year, some with two generations)
Eggs during winter and juveniles during summer. Adults in fall.
The fly population density
Flies typically overwinter as adults.
The development time from eggs to adults is about 1 – 3 weeks.
The fly populations increase rapidly as the temperature rises in the spring and summer.
When there is the first frost, most flies die. Only a tiny portion of the population survives throughout the winter.
Seasonal calling patterns in Gryllus Rubens
Fewer males called during the autumn than during the spring. (most flies in summer/fall, fewer in spring)
Autumn males were less likely to call at dusk, when flies were most active.
G. ovisopis produce no sound.
Evolution of animal communication
Fitness
(signaler) (receiver)
(-) (+) ---> no evolution of a signal (+) (-) ---> no evolution of a signal (+) (+) ---> evolution of a signal
Natural selection can cause signal changes to spread through a species only if both signalers and receivers drive net benefits from their participation in the system.
Types of information exchange
signaler(+) and receiver(+) = true communication
Signaler(0) and receiver(+) = eavesdropping
Signaler(-) and receiver(+) = exploitation
signaler(+) and receiver(0) = manipulation
signaler (+) and receiver(-) = deceit
True communication
- The provision of information occurs only because it benefits the signaler.
- The receiver must also benefit by having access to the provided information.
true communication —> evolution of a signal
Signal vs cue
signal:
≡ An act or structure that alters the behavior of another organism, which evolved because of that effect, and which is effective because the receiver’s response has also evolved
cue:
≡ a feature of the world, animate or inanimate, that can be used by an animal as a guide to future action
ex) A cricket calling song is a cue to the parasitic fly.
As a rule of thumb, signals benefit the sender, but cues do not.
Example of manipulation
Signaler: milk snakes
Receiver: potential predators
Milk snake looks like the coral snake which is poisonous. A signal that benefits the signaler and does nothing to the receiver.
Honest signal
Honesty is the provision of accurate information by the sender.
Deception is the provision of unreliable information.
Cooperative and manipulative views of communication
(1) Cooperative (classical) view of communication:
- Many signals were found to have evolved through the ritualization of behaviors that were functionally appropriate to the context in which the signals are now given.
- Signals were believed to be honest indicators of underlying motivations.
(2) Manipulative view of communication:
- Dawkins and Krebs in 1970s
- Senders were best characterized as “deceitful manipulators” trying to mask their true intentions and trick receivers into actions benefiting senders.
- Receivers in turn were characterized as “mind readers” trying to discount false signals, anticipate the true intent of the sender, and thus identify their own best countermove.
Handicap signal
Amotz Zahavi
Handicap signals are those with an associated production cost, such as energy expenditure, predation risk, development investment, or vulnerability to attack.
Handicap signals are strategic, in the sense that all senders can in principle make all signal variants, but it costs more to make a bigger or more intense signal.
Senders are assumed to vary in their ability to bear these production costs, or in their ability to reap benefits from a given amount of display investment. The different benefit/cost trade-off optima for individuals of different abilities lead to a positive association between display intensity and sender characteristics, which can be highly informative to receivers.
Handicap signals refer to signals made reliable by cost/benefit trade-offs.
Handicap principle is now accepted as an important mechanism for the evolution of reliable signals.
Deep croaks deter rivals in European toads
Why don’t small males pretend to be large by giving low-pitched calls?
→They can’t. Body mass determines the pitch of the signal that a male toad can generate.
—> honest signal
low pitch croak:
- fewer attacks
- less time spent attacking
Flash signal evolution in the firefly
Each species of Photinus has its own flash pattern.
A female may respond to male signal by giving a flash of her own after precise time interval
Aggressive mimicry
The female Photuris firefly is feeding on a male Photinus firefly that she lured to his death by imitating the flashes given by females of his species. —-> deceit
How can deception evolve?
Deception: costly behavioral traits:
- Phonotaxis of parasitic flies to cricket calling songs
- aggressive mimicry in fireflies
Bold males:
- explore possible flashes
- may be devoured by an exploitative Photuris signaler
Cautious males:
- may live longer
- probably ignore some females of their own species
Possible scenarios
low predation pressure from illegitimate signalers —> maintenance of a signal
High predation pressure from illegitimate signalers —> no more communication
Exploitation theory og signal deception
Costly behavioral traits have been shown to occur because certain individuals (illegitimate signalers or illegitimate receivers) are able to exploit an otherwise adaptive communication system for their own benefit.
The response of a male Photinus to certain flashes increase his fitness, even though one of the costs of responding is the chance that he will be devoured by an exploitive Photuris signaler.
An adaptation need not be perfect, but it must contribute more to fitness on average than other possible alternative traits.
