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2nd Year: Evolutionary Genetics > Frequency-dependent selection > Flashcards

Flashcards in Frequency-dependent selection Deck (31)
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1
Q

What is frequency dependent selection?

A

When the fitness of a genotype depends on its frequency within a population, i.e. the same genotype will have a different fitness when common and when rare.

2
Q

What is frequency dependent selection an example of?

A

Flexibility fitness

3
Q

What is positive frequency dependence?

A

A morph increases in fitness as it increases in frequency.

4
Q

Explain how positive frequency dependence works using the example species A and B.

A

As A increases in fitness it becomes more successful, causing the numbers of B to decline. Because B is rare it is unsuccessful, and vice versa.

5
Q

Define the point of neutrality.

A

When both species have the same fitness, an equilibrium.

6
Q

Is the point of neutrality stable in positive frequency dependence? Why, why not?

A

No - if the equilibrium is disturbed in either direction, for example by genetic drift, it will lead to fixation.

7
Q

Give an example of positive frequency dependent selection in nature.

A

Mullerian mimicry in butterflies. The more common their phenotypes are, the more likely (young) predators know not to eat them, thus they become more successful in commonality.

8
Q

What does ‘geographical locality among the same species’ mean?

A

Members of the same species that look different depending on location.

9
Q

What is negative frequency dependence?

A

When a morph becomes less successful when it is common, i.e. it becomes fitter when it is rare.

10
Q

Is the point of neutrality in negative frequency dependence stable? Why, Why not?

A

Yes, because the fitness differential pushes a population back to equilibrium.

11
Q

Explain how negative frequency dependence is maintained using the example species A.

A

If species A grows in number this has a detrimental effect on their fitness, thus selection acts to remove individuals from the population until A is at a low frequency where it thrives.

12
Q

Give an example of negative frequency dependence in nature.

A

Sex ratios: if sex ratios become imbalanced, the rarer sex will have a greater than average contribution to the next generation in the form of gametes. This will restore parity.

13
Q

What is meant by an ‘evolutionary sustainable strategy’ (ESS)?

A

One that is un-invadable. ‘If all members of a population adopt the ESS, no mutant strategy can invade’.

14
Q

What is ‘game theory’ in the context of evolutionary biology?

A

A method for describing the constraints of ritualised contests between animals as they compete for resources.

15
Q

HAWK-DOVE theory is the simplest example of game theory. Describe the role of a) hawk and b) dove.

A

a) Hawk fights unconventionally without restraint. It only stops if it wins or is seriously injured.
b) Dove only ever threatens and runs away at signs of aggression, thus it is never injured.

16
Q

What happens if 2 doves contest?

A

Time is wasted before either of them wins because they keep running away from each other (pussies).

17
Q

HAWK-DOVE assumes there is asexual inheritance of behaviour. What does this mean?

A

That offspring behave exactly as the parents do. Hawks produce hawks and doves produce doves.

18
Q

In HAWK-DOVE games, the players meet in pairs in frequencies representative of the population. True or false?

A

True.

19
Q

We assign pay-offs to the outcome of each contest. What do these pay-offs indicate.

A

Increments or decrements of fitness.

20
Q

What are the 3 main pay-offs in HAWK-DOVE games?

A
  1. Victory
  2. Injury
  3. Time-wasting
21
Q

How do you work out the average pay-off when two hawks meet?

A

Pay-off for victory plus pay-off for injury (as one hawk wins and the other loses) over 2 (because there are 2 hawks).

22
Q

How do you work out the average pay-off when two doves meet?

A

Pay-off for victory plus pay-off for time-wasting (as one dove won and the other just wasted time), over 2 (because there are 2 doves).

23
Q

What are the pay-offs to a) a hawk and b) a dove when they meet?

A

a) The pay-off assigned to victory, hawk always beats dove

b) Always 0 - the animal runs away and is not injured and does not waste time

24
Q

If an ESS is said to be pure what does this mean?

A

It is 100% hawk or 100% dove.

25
Q

An ESS cannot be mixed. True or false?

A

False - ESSs are often a mix of hawk and dove.

26
Q

How do you assess which is the ESS? Imagine you think the ESS might be 100% hawk.

A

Think of all the interactions in a 100% hawk population, i.e. hawk meets hawk or dove meets hawk. Compare the pay-offs to each player in these interactions. If the pay-off to dove is higher than to hawk, 100% hawk cannot be the ESS.

27
Q

If the ESS is mixed we can use algebra to deduce the proportions of hawk and dove. How?

N.B. this is probably not the best way to remember it but it will help you (maths retard)

A

Imagine a pay-off matrix. ‘Pay-off to’ are the rows and ‘when meeting a’ are the columns. Each column is assigned a letter, e.g. hawk is given X and dove is given Y. Then you put this into an equation and solve it. It will look like:
pay-off to hawk (X) when meeting a hawk plus pay-off to hawk when meeting a dove (Y) = pay-off to dove when meeting a hawk (X) plus pay-off to dove when meeting a dove (Y). ALL PAY-OFFS TO HAWK ON THE LEFT, ALL PAY-OFFS TO DOVE ON THE RIGHT. Effectively ‘X’ means ‘when meeting a hawk’ and ‘Y’ means ‘when meeting a dove’.

28
Q

In nature under what 2 conditions is more-hawkish behaviour observed?

A
  1. When the resource is of higher value

3. When the cost of injury is low

29
Q

Give an example of when cost of injury is low in nature.

A

Male salmon die after reproduction, so getting seriously injured in contests for mates is no biggie.

30
Q

Give an example of when the resource is of higher value in nature.

A

Male newts fight harder for larger females, as size is directly correlated to fertility.

31
Q

What is Bourgeois theory?

A

It brings ownership into games: a resource cannot be shared. Resource owners act as hawks and intruders as doves. Ownership is always respected.