Download Animal Communication 3

Offspring-parent signaling:
Animal Communication 3
• Parents and offspring share an interest in keeping offspring alive.
• Parents under selection to allocate food in relation to the hunger of each
offspring.
• Individual offspring selected to mislead parents as to true level of need, since
they are selected to acquire more food than parents are selected to give.
• Begging seen as an expression of this conflict, with offspring attempting to
manipulate parents into providing extra food.
• How is honesty maintained?
•
Consider the benefit of begging from the point of view of a recently fed vs a
hungry individual:
•
Now consider the cost of begging as well:
Cost of begging
Fitness
Fitness
Benefit to
HUNGRY
offspring
Benefit to
HUNGRY
offspring
Benefit to
FED
offspring
Benefit to
FED
offspring
Begging Intensity
Begging Intensity
Optimal begging intensity for HUNGRY offspring
Optimal begging intensity for FED offspring
Canary chicks
Honest signaling:
•
Captive nests, where all chicks received the same amount of food.
•
Chicks experimentally induced to beg for 10 sec or 60 sec before being fed.
•
High begging chicks gained weight at a much lower rate, demonstrating a
metabolic cost to begging.
• By increasing resistance to a signal, receivers force signalers to
exaggerate.
• This eventually imposes significant costs, ensuring the honesty of the
signal.
• But is this evolutionarily stable?
• Selection will always act on signalers to develop ways to REDUCE the
cost of signaling.
• How? - Can anyone guess?
(Kilner 2001, PNAS vol. 98)
Cosmetics: reducing the cost of a signal
•
Universal in humans.
•
Exaggerates or simulates costly, age dependent or state dependent signals:
Other species do similar things:
•
Bearded vultures stain feathers with iron oxide from mud. Adults are more
intensely stained than juveniles, and females are more intensely stained than males.
•
Superb fairy wren males pick up bright yellow flower petals and present these to
females.
But this just re-ignites the Arms race
Dishonesty can be common and apparently stable:
• Brood parasite eggs and chicks
Signaler-receiver arms races are common
• Klepto-parasitic fork tailed drongos
Eventually lead to periods of stable honesty
• Deceptive ‘Bee’ orchids
• Deep sea angler fish…
Interrupted by brief periods of dishonesty,
which start new arms races.
Is this the whole story?
• Mimicry
– Adaptive resemblance of one species (the mimic) to another
(the model)
• Batesian mimicry
– A palatable mimic resembles an unpalatable model
• Aggressive mimicry
– Predator mimics a nonthreatening model
These systems have characteristic shared features:
• A small proportion of dishonest individuals survive within a
larger population of honest signalers.
• Suggests some sort of ESS, with frequency-dependent payoffs.
• How might this work?
Figure 6.24. Salamander mimicry. Ensatina salamander mimic (right) and its
toxic model (left). Note their yellow eye coloration and orange ventral surface.
Receivers must decide whether & how to respond to a
given stimulus, with 4 possible consequences:
Acceptance threshold
• Receivers should consider the payoffs to be obtained from
responding to or ignoring a signal.
Frequency
Signal
• The optimal threshold depends on
▪ The relative frequency of signals vs noise;
▪ The economics of the four outcomes
• We expect receivers to set their acceptance thresholds such that, on
average, the benefits of responding outweigh the costs.
Noise
Signal characteristics
Correct acceptance
Correct rejection
False alarm
Missed detection
As the cost of missed detections increases, expect receivers to shift
their acceptance threshold, increasing their correct detections, but
at the cost of more false alarms:
When the costs of a false alarm are high relative to a missed
detection, expect receivers to minimize false alarms, accepting
more missed detections:
Threshold becomes more stringent
Threshold becomes more
inclusive
Frequency
Signal
Frequency
Noise
Signal
Signal characteristics
Signal characteristics
False alarm
Missed detection
Noise
False alarm
Missed detection
http://www.youtube.com/watch?v=3FEX1XtNbwo
Cuckoos versus hosts
• Cuckoo family comprises 140 species
• 60% parental: build their own nests
& raise their young
• 40% are brood parasites
Robin
• Common cuckoo has several
Pied wagtail
genetically distinct races, each of
which specializes on one host species
Dunnock
and lays a distinctive egg type that
matches that of its host:
Reed Warbler
Egg mimicry by cuckoos evolves in response to host discrimination
The color match between cuckoo and host eggs varies across the
different host races of cuckoo, with a better match when the hosts
are stronger discriminators
Cuckoo eggs
Meadow Pipit
Great reed
warbler
Stoddard & Stevens 2011 Evolution Vol. 65
Cuckoos have evolved in response to hosts
Hosts have evolved in response to cuckoos
Experimental parasitism of reed warbler nests with model cuckoo eggs
reveals that hosts are more likely to reject the model egg if
• it is a poorer match of the hosts’ own eggs;
• it is laid before the hosts themselves begin to lay;
• it is laid at dawn, when the hosts themselves lay;
• if the hosts are alerted by the sight of a cuckoo on the nest.
Cuckoos and reed warblers:
•
Parents are not able to discriminate perfectly between own eggs and cuckoo eggs.
•
Still make some recognition errors:
– 70% of time correct
– 30% of time reject own eggs
•
Host reproductive success
Host response
In each nest, host can choose to accept or reject a ‘suspicious’ egg, with 4 possible outcomes :
Not parasitised nest
Parasitised nest
4 host eggs
3 host + 1 cuckoo
Accept
Correct acceptance:
4 eggs
Missed detection:
0 eggs
Reject
False alarm:
3 eggs
Correct detection:
(0.7 x 3) + (0.3x0)
= 2.1 eggs
Host reproductive success
Host response
Not parasitised nest
Parasitised nest
4 host eggs
3 host + 1 cuckoo
Accept
Correct acceptance:
4 eggs
Missed detection:
0 eggs
Reject
False alarm:
3 eggs
Correct detection:
(0.7 x 3) + (0.3 x 0)
= 2.1 eggs
• It’s clearly better to reject if parasitized (2.1>0) but to accept if not parasitized
(4>3).
• However, the probability of being parasitized can also have an effect
Davies et al. 1996 Proceedings of
the Royal Society of London
Series B, Vol. 263
Fork tailed drongos and pied babblers
• Babblers forage in family groups, in the open, on the ground.
• Under heavy predation pressure, so individuals take turns to be a sentinel.
• Being a sentinel is costly (lost foraging, possible risk of predation).
• In reality, probability of parasitism is extremely low (between 1 – 2 %).
• Therefore generally best to ‘Accept everything’.
• Unless obtain evidence that the risk of parasitism has increased.
• Rejection MUCH more likely if parents SEE a cuckoo.
• Fork tailed drongos follow foraging babbler groups.
• Perch above the group, like a sentinel.
• Small babbler groups (3-4) let drongos stay, large groups (8-14) chase them away
– Despite the risk of klepto-parasitism, the value of a semi-reliable sentinel is high enough
for small groups to accept them.
• Give two types of alarm call:
– Real alarms, in response to genuine predators.
– False alarms, when a babbler finds a valuable food item.
• Recent experiments suggest that when the risk of predation increases, babblers are more
likely to react to drongo alarm calls
– The cost of ignoring an alarm has increased.
• False alarms are usually mimicked babbler calls.
• Babblers face several decisions:
– Chase drongo away or let it stay.
– Respond to drongo alarm calls or ignore them.
Key points:
• Where conflicts of interest arise, selection will favor low-cost
behavioral mechanisms which alter the behavior of other
individuals (‘signals’).
Animal Cognition 1
• Individuals exposed to these (‘receivers’) will be under
selection to extract accurate information and only respond when
the benefits outweigh the costs.
• This will tend to drive arms races between signalers and
receivers, with two possible outcomes:
– Stable honesty, with honesty imposed by the cost of signaling.
– Low levels of dishonesty, maintained by frequency-dependent selection.
"Now we must redefine tool, redefine Man, or accept
chimpanzees as humans."
- Dr. Louis Leakey -
What makes us human?
Which mental abilities set us apart from all other
animals?
Evolution of learning
Learning
• modification of behavior based on experience
• permits animals to deal with environmental unpredictability or
instability
• permits fine-tuning to local environments
• Should learning evolve in a fixed
or dynamic world? Neither!
• Fixed world
– No need to learn because of
environmental constancy
• Dynamic (unpredictable) world
– Learning is not beneficial because of
unpredictable changes in the
environment
• The real world is intermediate
and so learning is adaptive and
expected to evolve
Adaptive value of learning
Constraints on learning
(a.k.a. “biased” learning)
• Behaviorists held that the evolutionary history of an
animal was unimportant with respect to learning
– Law of equipotentiality
•
Same sort of learning occurs in
all animals
•
Any stimulus can be associated
with any task
•
Ignores selection for nichespecific learning tasks
• Natural selection operates on the ability to learn (Hinde,
1966)
• Animals come into the world prepared to learn some
things more easily than others
– Preparedness: genetically based predisposition to learn
certain things, and to make mental associations between
some stimuli but not others
“Biased” Learning
John Garcia’s ‘bright-noisy’ water experiments
Some animals learn a task much more readily
than others
Polygynous
Monogamous
Fig 3.43
Types of Learning
• Non-associative learning
Habituation
Decline in the magnitude of a reflexive response when an irrelevant
stimulus is repeated several times in succession
– No association is formed between two events or stimuli, only
strengthening or weakening of preexisting stimulus-response
sequences
• Habituation, Sensitization
• Associative Learning
– A mental connection is made between two stimuli or events that were
level of
response
Aplysia
previously unrelated
• Imprinting
• Classical & operant conditioning
• Social learning
5
10
stimulus number
15
Sensitization
Tendency to respond more strongly to repeated weak stimuli after the
organism has been aroused by a noxious or intense stimulus
Types of Learning
• Non-associative learning
– No association is formed between two events or stimuli, only
strengthening or weakening of preexisting stimulus-response
electric shock
sequences
• Habituation, Sensitization
• Associative Learning
level of
response
Aplysia
– A mental connection is made between two stimuli or events that were
previously unrelated
• Imprinting
• Classical & operant conditioning
5
10
stimulus number
15
• Social learning
Associativelearning
Sofundamentaltothewaythatanimalslearn,thatsomeanimals
evenevolvetolookcertainwaystotakeadvantageofit(e.g.
Aposematism).
A male mouse will carefully inspect a female mouse the first
time they meet. However, if the same female is repeatedly
placed in the male’s cage, he will stop inspecting her. This is
an example of:
a) Operant conditioning
b) Classical conditioning
c) Habituation
d) Imprinting
e) Sensitization
Stimulus
Blackandorangepattern
Outcome
Disgust/nausea
Infuture:
Avoid!
Learning is associated with neurological changes
• Nerves are composed
of neurons
• Neurons
– Cells that receive and
transfer electrical and
chemical signals
Neurotransmitters and learning in chicks
• Research question: Is the release of
neurotransmitters from the presynaptic neuron
associated with imprinting learning? (Meredith et
al. 2004)
Learning is associated with neurological
changes
• Synapse
– Junction between two
neurons
– Chemical signals
transfer information
between two neurons
Neurotransmitters and learning in chicks
• Methods:
– Domestic chicken chicks (Gallus
gallus domesticus)
– Control group – no visual stimulus
for imprinting
– Experimental groups – trained with
visual imprinting stimulus (red box
or blue cylinder)
• Trained on running wheel
• Measured movement toward stimulus
– Measured amino acid transmitters in
intermediate and medial portions of
hyperstriatum ventrale (IMHV)
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Neurotransmitters and learning in chicks
Neurotransmitters and learning in chicks
• Results
• Results
– Trained chicks
had higher
glutamate
levels
– Chicks with higher
preference scores had
higher amount of
GABA in their brain
• Conclusion
– Neurotransmitters
appear to play a role in
imprinting
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Memory is associated with changes in the
brain
• Memory
– Retention of a learned experience
• Neural plasticity
Dendritic spines and learning in mice
• Research question: Is dendritic spine formation
associated with learning in mice? (Yang, Pan, & Gan
2009)
– Structural changes in the brain
– Especially in the number and chemical strength of
synapses between neurons
• Dendritic spines
– Small protuberances on a dendrite that receive
synaptic inputs
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Dendritic spines and learning in mice
• Methods:
– Controls: no training
– Experimental: mice
trained to run on a
rotorod
– Measured formation of
new dendritic spines
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Dendritic spines and learning in mice
• Results:
– Mice that developed more
dendritic spines performed
better on the rotorod
• Conclusion:
– The formation of new
dendritic spines is
associated with learning
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Dendritic spines and learning in mice
• Results:
– Mice that learned new
skill (running on
rotorod) had higher
levels of dendritic
spine formation
From Nordell and Valone, Animal Behavior: Concepts, Methods, and Applications, © 2014 by Oxford University Press
Some animals learn a task much more readily
than others
Polygynous
Monogamous