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BEHAVIOURAL TRAITS UNDER NATURAL SELECTION

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Title: BEHAVIOURAL TRAITS UNDER NATURAL SELECTION


1
BEHAVIOURAL TRAITS UNDER NATURAL SELECTION
SHWETA PATEL Id no. - 42537
2
What is a Trait ?
Behaviour The response of an organism to
signals from the environment.
Behaviorual Ecology is the study of how animals
interact with their environment and the survival
value of behaviours.
  • A characteristic of some organism, like how it
    looks or acts. can be passed down from parents to
    offspring (inherited) and also can be learned

3
Ecology
Population Biology
Evolutionary Biology
Genetics
Ethology
Sociobiology
Endocrinology
Neurophysiology
Physiology
4
Natural selection
  • Natural selection organisms with the most
    favourable traits survive in the natural
    environment and reproduce most successfully.
  • The concept of selection is central to Darwin's
    theory of evolution. Behaviours that increase
    mating opportunities and survival will enhance
    reproductive success.

5
Three types of Natural Selection
  • Directional
  • Allele frequencies shift to favor individuals at
    one extreme of the normal range
  • Only one side of the distribution reproduce
  • Population looks different over time
  • Stabilizing
  • Favors individuals with an average genetic makeup
  • Only the middle reproduce
  • Population looks more similar over time
  • (eliminates extremes)
  • Diversifying (Disruptive)
  • Environmental conditions favor individuals at
    both ends of the genetic spectrum
  • Population split into two groups

6
Levels of Analysis in Ethology
Proximate Causes
Ultimate Causes
Genetic/Developmental Mechanisms
Sensory/Motor Mechanisms
Historical Pathways
Selective Processes
-adaptive context ?
-nervous systems for stimulus
detection -hormone systems for adjusting
response levels -muscles for carrying out
responses
-evolutionary development of a trait
  • -effects of heredity
  • -development of sensory-
  • motor systems
  • gene-environment
  • interactions

Why?
How?
7
The Nobel Prize in Physiology or Medicine 1973
  • Karl von Frisch, Konrad Lorenz, and Nikolaas
    Tinbergen "for their discoveries concerning
    organization and elicitation of individual and
    social behavior patterns
  • Karl von Frisch- Made major contributions to
    the study of honey bees, their ability to
    communicate to hive mates about food sources with
    the waggle dance, use of pheromones, and their
    ability to see in color and in ultraviolet and
    polarized light.
  • Konrad Lorenz- Studied instincts and fixed
    action patterns in birds, and later became
    interested in human behaviours.
  • Nikolaas Tinbergen- Studied fish, birds and
    insects in nature and the laboratory and later
    autism.

8
Behaviour can Evolve through Natural Selection
  • There is variation in behaviours (feeding
    behaviours, attack behaviours, Foraging
    behaviours etc).
  • This variation depends on environment and
    animals survival.
  • Some behavioural components are genetic - passed
    down from parent to offspring.
  • Two Categories of Behaviour
  • Innate or Unlearned Behaviour
  • Learned Behaviour or Conditioning

9
Innate Behaviour
  • Innate behaviour is genetically
    programmed. Individuals inherit a suite of
    behaviours (often called an Ethogram).
  •   innate behaviours will always be 
  • Heritable -encoded in DNA and passed from
    generation to generation
  • Intrinsic - present in animals raised in
    isolation from others
  • Stereotypic - performed in the same way each time
    by each individual
  • Inflexible - not modified by development or
    experience
  • Consummate - fully developed or expressed at
    first performance

10
Innate behaviour Kinesis
  • Kinesis-strong change in activity or turning
    rate in response to stimulus.
  • Ex-
  • Sow bugs become more active in dry areas and less
    active in humid areas.
  • Woodlice become more active in dry areas and less
    in humid areas.

11
  • Fig 51.7a

12
  • Fixed action pattern (FAP)
  • A sequence of behavioral acts that is essentially
    unchangeable and usually carried to completion
    once initiated.
  • FAP is triggered by an external sensory stimulus
    known as a sign stimulus
  • FAP usually occurs in a series of actions the
    same way every time.
  • Releaser is used for stimuli that have evolved to
    facilitate communication between animals of the
    same species
  • Sign stimuli are features of an animal's
    environment to which it reacts in a particular
    way
  • For example-
  • The fly orchid is a plant that looks like an
    insect which helps it attract pollinators.
  •  

13
Learned Behaviour
  • Learning as a persistent change in behaviour that
    occurs as a result of experience.  Since a new
    born nymph or larva has no prior experience, its
    first behaviours will be entirely innate. learned
    behaviours will always be-
  • Non heritable -- acquired only through
    observation or experience
  • Extrinsic -- absent in animals raised in
    isolation from others
  • Per mutable -- pattern or sequence may change
    over time
  • Adaptable -- capable of modification to suit
    changing conditions
  • Progressive -- subject to improvement through
    practice

14
  • Habituation - Loss of responsiveness to stimuli
    that do not convey useful information (cry wolf
    effect).
  • Ex-
  • A puff of air on the cerci of a cockroach will
    cause the animal to scamper away.  But repeating
    the same stimulus over and over will lead to a
    decrease in the response and eventually to no
    response at all. 
  • In some insect populations, widespread use of sex
    pheromone will disrupt mating behaviour.  smell
    like a virgin female, males become habituated to
    the odour and stop responding to the signal. 

15
  • Classical Conditioning - Is learning to associate
    one stimulus with another, unrelated stimulus. 
  • for example-
  • Honey bees, learn to associate floral colours
    and fragrances with the presence of nectar.  They
    can be "trained" to collect sugar water from
    coloured dishes on a feeding table.  If a blue
    dish with pure water sits next to a yellow dish
    with sugar water, worker bees will quickly learn
    to associate "yellow" with "food.When solutions
    in the two dishes are suddenly swapped , the bees
    will ignore blue and continue to forage at yellow
    until they eventually "learn" (by trial and
    error) to look for the blue dish.

16
  • Latent Learning involves memory of patterns or
    events when there is no apparent reward or
    punishment associated with the behaviour. 
  • for example-
  • A sand wasp learns the location of her nest site
    by taking a short reconnaissance flight each time
    she leaves the nest.  She remembers the pattern
    of surrounding landmarks to help her find the
    nest when she returns. 
  • worker ants can remember a series of landmarks
    along a trail and follow them (in reverse order)
    back home to the nest site. 
  • Honey bees also show latent learning when they
    follow the waggle dance of a forager and then use
    that information to find the reported nectar
    source.

17
Operant Conditioning - learning in which an
animal is rewarded or punished for performing a
behaviour. Ex- Cockroaches learning to run
through a simple maize to find food is a simple
example of operant conditioning (also known as
instrumental learning). Rats in Skinner box  
trial by error learning
  • Imprinting- Is a special case of programmed
    learning that occurs early in life and only
    within a short time-window known as the "critical
    period". 
  • Ex-
  • Fruit fly larvae will imprint on the taste and
    smell of their food.  If reared on a diet that
    contains apple extract, adult females will show a
    strong preference for apples when they eventually
    search for a place to lay their own eggs. 

18
Proximate and ultimate perspectives on imprinting
in graylag geese
19
In a classic experiment, Niko Tinbergen Tinbergen'
s Observations on the Bee Wolf - Philanthus
triangulum
1.Observation - Female flies in a circle before
going to hunt.
3. Prediction - Female will return to a
landmark to find the nest.
2. Hypothesis - Female is using landmarks to find
the nest.
4. Test - Place an artificial landmark around
the nest and move it when the female is away
5. Result - Female orients to new landmark.
6. Confirm hypothesis ?
20
Auditory Communication
  • Experiments with various insects

21
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22
Behavioural traits evolve by natural selection
  • Agelenopis aperta a funnel web spider occurs in
    both desert and riparian (riverside) woodland.
  • Desert spiders (which occur in food-poor
    habitat) are much more aggressive and attack
    potential prey much more quickly than riverine
    spiders.

23
  • 51.19

24
Optimal foraging
In optimal foraging organisms maximize their food
intake while minimizing their energy expenditure
and risk of mortality.
  • Zachs crow work
  • Crows feeding on whelks (marine snails) fly up
    and drop the whelks on rocks to break them.
  • Height from which a shell is dropped affects its
    probability of breaking.
  • Dropping from greater height increases
    probability of breaking shell, but it costs
    energy to fly up.

25
  • Fig 51.22

26
Risk of predation is one of the most significant
potential costs to a forager
  • Mule deer are preyed on by mountain lions
    throughout their range. Risk of predation varied
    greatly upon areas.
  •   Mountain lions killed most mule deer at forest
    edges.
  •   Few were killed in open areas and forest
    interiors.
  • Mule deer feed predominantly in open areas,
    avoiding forest edges and forest interiors. When
    deer are at the forest edge, they spend
    significantly more time scanning their
    surroundings.

27
Risk of Predation
  • Bluegill sunfish feeding on Daphnia of different
    sizes at different prey densities
  • At low densities, there was little selectivity
  • At high prey densities, there was significant
    selectivity for feeding on larger prey sizes
  • This minimizes capture and handling costs and
    maximizes payoff to the fish

28
Environment influences the behaviour
  • The California mouse (Peromyscus californicus) is
    monogamous and like male prairie voles, male
    California mice are highly aggressive to other
    mice and provide considerable parental care.   
  • Researchers placed new born California mice in
    the nests of white-footed mice and vice-versa.
    This cross-fostering changed the behaviour of
    both species.
  • Cross-fostered California mice provided less
    parental care and were less aggressive toward
    intruders when they grew up and reared their own
    young.
  • Their brains had reduced levels of AVP, compared
    with California mice raised by their own parents

29
Mating Behaviour Mate Choice
  • Mating behaviour is the result of sexual
    selection.
  • As other behaviours, must enhance reproductive
    success (fitness).

30
Sperm competition
  • Males compete not only to mate with females, but
    frequently engage in sperm competition as well.
    More sperm a male can insert the higher his
    chances of fertilizing eggs (like a lottery).
  • Ex-
  • Males also commonly remove other males sperm
    (e.g. damselflies have a penis with spines), plug
    up females reproductive tract (many insects) or
    guard females against other males.

Altruistic Behaviour
  • behaviour that appears to decrease individual
    fitness but increases the fitness of others.
  • For example-
  • Many animals give alarm calls that warn others
    of a predator but put the caller at risk.
  • In bees, ants and other social insects many
    individuals do not reproduce themselves but
    assist another individual (the queen) to
    reproduce.

31
Behavioural traits evolve by natural selection
Drosophila foraging
  • In lab studies in low density populations of
    Drosophila for S allele increased in frequency.
    Opposite was true in high density populations.
  • In low density populations for S individuals did
    not waste energy traveling long distances for
    food. In high-density populations for R allele
    caused larvae to move beyond areas of food
    depletion.

32
Behavioural traits evolve by natural selection-
Drosophila foraging
  • Two alleles in a gene for foraging for R and for
    S.
  • For R rover larva moves more than average.
  • For S sitter larva moves less than average.

Foraging pathways of individual Drosophila larvae
33
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