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Chapter 6

LIFESCI 2D03 Chapter Notes - Chapter 6: Frequency-Dependent Selection, Strawberry Poison-Dart Frog, Natural Selection

Life Sciences
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Rashid Khan

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Animal Behaviour Chapter 6
The evolution and accuracy of signals will depend on the benefits and costs of signal production
and the fitness interests of those involved.
6.1 Communication occurs when a specialized signal from one individual influences the
behaviour of another.
- Communication: the process in which a specialized signal produced by one individual
affects the behaviour of another
Signaler: an individual that produces a signal
Signal receiver: an individual that detects a signal
- Signal: a packet of energy or matter generated from a display or action of a signaler that
travels to a receiver.
Can be physiological traits, morphological traits, or behaviours
Honeybees and the Waggle Dance (von Frisch 1973)
- Individual honeybees in a colony leave the hive to scout out a rich food source and return
to the hive to recruit others to help exploit it. The scout communicates the location of the
food to other bees using the waggle dance: the scout moves in a figure-eight pattern on a
vertical wall of the honeycomb.
- Waggle dance: a behaviour performed by a honeybee scout that recruits workers to a food
The duration of wagging in the linear movement of the dance indicates the location
of the food. Every 75msec of waggling translates into a distance of approximately
100m from the hive.
The waggle dance describes the direction of the food source relative to an
imaginary line that runs from the hive to the sun.
- Travel times of bees are longer than expected, so it was proposed that the bees doing the
dance present the odour of the food source, allowing recruits to find it on their own.
Wenner and Johnson proposed that new recruits fly downwind before starting their search
and use olfaction as a method of locating the food by flying upwind in a zigzag pattern
back to the hive.
Odor or the Dance in Bees? (Riley et al. 2005)
- Research question: Which is more important in honeybee’s localization of food: odor or the
waggle dance?
- Methods:
Examined the flight paths of recruits that viewed the scout waggle dance from a
hive placed in a large, flat, mowed field.
The only available food source was located at a feeding source.
Wind speed and direction were recorded at ten second intervals from four
locations surrounding the field and at the hive
In order to enter and leave the hive, bees had to pass through a clear plastic tube,
allowing researchers to mark the bees with numbered tags.
Transponders were placed on the backs of recruits who were released either at
the hive or at one of three locations 200-250m southwest of the hive.
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- Results:
In response to the waggle dance, bees flew 200m due east of the hive, whether
they were released at the hive or displaced before release.
The wind data indicated that no odor from the feeding station was available to the
bees at their release sites.
Bees were not able to accurately locate the food source in the absence of odour
cues, but used the waggle dance to find the general area.
- Conclusion: the waggle dance is a behavioural signal that allows individuals to travel to the
area of a distance food source, but bees then use local odour cues to find the food itself.
Auditory signals: Alarm Calls (Cheney & Seyfarth 1980)
- Alarm call: unique vocalizations produced by social animals when a predator is nearby
- The alarm calls of vervet monkeys (Chlorocebus pygeruthrus) differ in how they affect
- Individuals produce different alarm calls for different predators because each predator
represents a threat that requires a different behavioural response.
Leopard: bark call, receivers move up into trees
Eagle: cough call, receivers move into dense bushes
Snake: chutter, receivers stand erect and look into grass clumps
- It cannot be determined whether alarm calls identify the predator present or instruct other
monkeys what actions they should take. For example, vervet alarm calls may not mean
“leopard present”, but rather “climb a tree”.
Titmouse Alarm Calls (Courter & Ritchison 2010)
- Background information:
The tufted titmouse (Baeolophus bicolor) is a songbird that produces an alarm call
in response to a perched avian predator in order to recruit others to approach and
mob the predator.
The titmouse call is composed of three basic notes (Z, A, and D) and individuals
vary the number of D notes.
Mobbing behaviour, in which birds produce loud vocalizations, often harasses a
predator and can drive it away from an area.
The size of a predator negatively correlates the risk to a titmouse.
- Research question: Do titmouse alarm calls differ in responses that correlate with the size
and degree of threat posed by a perched avian predator?
- Prediction: The number of D notes produced in an alarm call indicates the degree of threat
posed by a predator.
- Methods:
Several feeding stations for titmice were set up
Lifelike models of six different birds were placed on platforms 1m from the feeding
stations, three of which were high-risk predators, two were low-risk predators, and
one was a non-predator control bird. In the second control, no model was
presented on the platform.
Models were uncovered once titmice were within 25m of the feeding station
Behaviour of the titmice was recorded for 6 minutes and all alarm calls were
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- Results:
The number of D notes produced per titmouse was higher in response to small,
high-risk predators compared to the number produced to large, low-risk predators
and controls.
The smaller the predator, the longer the mobbing response lasted.
- Conclusion: Titmice produce different alarm calls that lead to differences in the behaviour
of receivers, which correlate with varying levels of threat.
6.2 Signals are perceived by sensory systems and influenced by the environment
- Sensory receptor: nerve endings that respond to an internal or external environmental
- Chemoreceptor: a sensory receptor that detects chemical stimuli
Most primitive and universal sensory receptors
- Olfaction: the detection of airborne chemical stimuli
Olfactory signals can be transmitted by water or air, are long-lasting, and can
travel long distances.
Olfactory signals can be produced in variable amounts, allowing animals to vary
their strength.
- Gustation: the detection of dissolved chemicals, often within the mouth.
- Volatile: a chemical that can evaporate (become gaseous)
- There are two classes of chemical stimuli, both of which are volatile:
1. Odourant: a gaseous compound that is perceived as odourous
2. Pheromones: volatile organic compounds that are species specific and affect the
behaviour of another individual of the same species.
Pheromones can be used as a species-specific pest control method by
disruption of mating signals.
In ants, sentries at the nest entrance use tactile cues (antennal contact of the
outer cuticle that contains pheromones) to determine whether individuals
should be admitted to their nests or attacked. When the hydrocarbon signal
from the postpharyngeal gland of a non-nestmate is dissolved in a solution
and placed near an ant, it responds aggressively, indicating that there seems
to be a volatile component to the pheromonal signal.
- Photoreceptor: a specialized neuron that is sensitive to light
- Rod: a type of photoreceptor, sensitive to low light levels
- Cone: a type of photoreceptors for colour vision under bright light conditions
- Visual signals can be detected quickly to allow a rapid response, but are dependent upon
sufficient light levels and obstacles.
- Visual signals are most often used by diurnal organisms that interact over relatively short
distances in open habitats.
Habitat Structure and Visual Signals in Birds (Marchetti 1993)
- Background information:
Old World warblers live in a variety of forest habitats that vary in light intensity
The birds are mostly dull green in colour but differ in the number of bright colour
patches that occur on their wings, crown, rump, and tail.
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