Paul Overton - Lecture 2 - Sociobiology and Behavioural Ecology

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What is Paul Overton's lecture 2 about?
Sociobiology and Behavioural Ecology
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Evolutionary approach to behaviour has various names:
'Behavioural ecology', 'Sociobiology', 'Sociobiology: a new synthesis'
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'Behavioural ecology'
Stresses way that behavioural contribution to Darwinian fitness depends on ecology (food; enemies; nesting requirements etc.)
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Term coined by: Wilson 'Sociobiology: a new synthesis'
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'Sociobiology: a new synthesis'
Stresses merger of behaviour ('socio') and genetics ('biology)
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Central problem -
Explanation of altruism
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What is altruism?
Behaviour that increases survival and reproduction of other individuals at a cost to one's own survival and reproduction
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E.g. of altruism
A Belding's ground squirrel produces an alarm call when it detects a predator
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First major hypothesis of how altruism evolved
Kin Selection (Maynard Smith, 1964). Relatives (or kin) also have copies of an individual's genes. Gene proliferation can occur through care for relatives (when they reproduce). Acts may be phenotypically altruistic but genotypically selfish.
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Probability that relatives will share a particular gene =
Coefficient of relatedness (r)
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Diploid species - i.e.....
With pairs of chromosomes; one from each parent
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Egg + sperm fuse =
Each parent contributes 50% of genes
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Probability of any one gene being shared by parent and offspring (r) =
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r =
coefficient of relatedness
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r = ....for identical twins
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r = .....for siblings
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r = ....for grandparents + grandchildren
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r = ......for grandparents + great-grandchildren
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r can easily be calculated for....
Any relatives
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Relatives contribute to an individual's....
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Fitness (Darwinian) =
Measure of genes contributed to next generation
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What are the two components of fitness (Darwinian)
1. Direct Fitness - Component from personal reproduction. 2. Indirect Fitness - Component from reproduction of kin
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An individual's total fitness is called its....
Inclusive Fitness (Hamilton)
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Concepts of direct and indirect fitness help us to....
Understand how altruism arises amongst selfish individuals
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How does concepts of direct and indirect fitness help us to understand how altruism arises amongst selfish individuals?
Need to look at the costs and benefits of altruism. Frequency of an altruistic gene will increase (in the population) if fitness benefit to altruist is great greater than fitness cost: B > C (Hamilton's rule)
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What do we mean by 'fitness benefit' and 'fitness cost'?
Since we're talking about fitness ('measure of genes contributed to next generation')...costs (C) and benefits (B) are calculated in genetic terms (in 'genetic units')
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Fitness Costs
C depends on impact (of altruistic act) on Direct Fitness (personal reproduction) C = number of offspring (forgone) in next generation x r. Since these are your offspring, r = 0.5. Gives a value for C in 'genetic units'.
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Fitness Benefits
B depends on impact on Indirect Fitness (reproduction of kin). B = number of kin's offspring in next generation (as a result of altruism) x r. Value of r is variable (depends how genetically close helped kin are to you). Gives a value for B in units
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So, frequency of an altruistic gene will increase (in the population) if....
B > C or (Nk x r) genetic units > (Ns x 0.5) genetic units
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Nk =
Number of kin's offspring resulting
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Ns =
Number of own offspring forgone
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E.g. (1)
Gene for self sacrifice. If it causes you to sacrifice yourself prior to reproduction...On assumption that most people will produce 2 children. C (2 x r) = 2 x 0.5 = 1 (genetic unit).
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E.g. (2)
Gene will increase in frequency if act saves life of (e.g.) a brother/sister who goes on to have more than 4 children (r = 0.25). For 5 children: B > C. (B) 5 x 0.25 > (C) 2 x 0.5. (B) 1.25 > (C) 1.00
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E.g. Influence of indirect fitness on behaviour. Alarm calls in prairie dogs...
Live in social groups ('coteries'). Hoogland (1983) studied alarm calls elicited by a (stuffed) badger (natural predator).
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Alarm calls in prairie dogs...Alarm calls were more frequent when....
Kin were present. Offspring and non-descendent kin were just as effective
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E.g. (3)
In >200 species of birds and 120 species of mammals, some individuals spend part of lives helping others to reproduce. Helping in white fronted bee eaters (Kenya). Potential helpers - likelihood of helping closely linked to degree of relatedness
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Second major hypothesis of how altruism evolved
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Explain Mutualism
Cooperation may occur because each participant gains (net) survival/reproductive benefit.
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Third major hypothesis of how altruism evolved
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Explain manipulation
Donors may be 'tricked' into behaving altruistically.
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Example of manipulation
Cuckoo. 'Brood parasites' - lay eggs in nests of other species. Parasitises host nest during host's laying period (one egg per nest). Takes egg from host nest and replaces it with one of own; young eject rest. Young are raised for free.
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Before she lays her own egg, a female cuckoo....
Removes an egg from the host bird's nest
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Fourth major hypothesis of how altruism evolved
Reciprocal Altruism (Trivers)
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Explain Reciprocal Altruism
"You scratch my back this time and I'll scratch your back next time" Doesn't require participants to be related; however, if unrelated...problem of cheating (Because of temporal delay; unlike mutualism)
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To avoid cheating in reciprocal altruism...
May give rise to very good inter-individual recognition
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Example of reciprocity
Regurgitation of blood by vampire bats (Wilkinson) Some failed to obtain a blood meal during night. Beg blood from others in daytime roosts; often successful. Regurgitation only occurred between frequent roostmates (or relatives) Preferential
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What does the example of reciprocity suggest
That individuals were able to recognise each other
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Underlying assumption =
Individual selection
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Central problem -
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Kin selection =
Can increase (indirect) fitness by caring for kin
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Mutualism =
Cooperation may increase survival and reproduction of participants
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Manipulation =
Doners may be tricked into behaving altruistically
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Reciprocal altruism =
Individuals gain from repayment of altruistic act at future date.
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Evolutionary approach to behaviour has various names:


'Behavioural ecology', 'Sociobiology', 'Sociobiology: a new synthesis'

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'Behavioural ecology'


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'Sociobiology: a new synthesis'


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