Contrast Red Queen and the Wright Landscape metaphor

Question 1

Can adaptation be brought about by both abiotic and biotic changes?

Answer 1

Yes

Question 2

Give examples of abiotic changes.

Answer 2

Climatic variables like temperature or rainfall

Question 3

Give examples of biotic changes.

Answer 3

New predator, parasite or competitor introduction.

Question 4

Are abiotic changes fast?

Answer 4

No

Question 5

Are biotic changes fast?

Answer 5

Yes

Question 6

Which is better for modelling abiotic changes, Red Queen or Wright Metaphor? Why?

Answer 6

Wright metaphor, because it is more rigid

Question 7

Which is better for modelling biotic changes, Red Queen or Wright Metaphor? Why?

Answer 7

Red Queen, as it is better at explaining dynamic and rapid changes

Question 8

Who created the Wright Metaphor and when?

Answer 8

Sewell Wright in 1932

Question 9

How does the Wright Metaphor visualise reproductive fitness?

Answer 9

As a topology, where peaks are fitness optima and troughs are fitness minima

Question 10

What does the position of an individual in the landscape depend on?

Answer 10

Their genetic composition

Question 11

In the Wright Metaphor, does an individual’s position on the topology change?

Answer 11

No

Question 12

In the Wright Metaphor, what causes the distribution of individuals to change?

Answer 12

Changes to population allele frequency

I think basically the topology changes but the individuals stay in the same position

Question 13

In the Wright Metaphor, information is conveyed by a combination of…

Answer 13

landscape topology and individual position

Question 14

In the Wright Metaphor, if the topology is rugged, and peaks are steeper, what does this show?

Answer 14

That selection is stronger and there is greater disparity in fitness between genotypes

Question 15

In the Wright Metaphor, if the topology is broader, and peaks are flatter, what does this show?

Answer 15

That selection is weaker and there is less disparity in fitness between genotypes

Question 16

In the Wright Metaphor, what does it show if individuals are clustered around a peak?

Answer 16

Mutation rate is low, allowing more individuals to achieve optimum fitness

Question 17

In the Wright Metaphor, what does it show if there are fewer individuals at the peak?

Answer 17

Mutation rate is high and less individuals have achieved optimum fitness

Question 18

Populations always move down peaks. True or false?

Answer 18

False, they only ever move UP

Question 19

Why can individuals only move up peaks?

Answer 19

Because deleterious mutations are removed by selection, so organism fitness either stays the same or improves (moves up)

Question 20

What is a hill-climbing mutation?

Answer 20

Beneficial mutations of small effect that allow movement of a whole population up a peak

The mutation initially arose in one organism but then spread through the population as it was advantageous

Question 21

Why are hill-climbing mutations generally of small effect?

Answer 21

As large mutations are often deleterious

Question 22

Rugged fitness landscapes, where there are multiple optima, contain numerous peaks separated by adaptive valleys. How do individuals move peaks?

Answer 22

In a phenomena called ‘peak jumping’ as they cannot move down in the fitness landscape

Question 23

Peak-jumping occurs via two major mechanisms. What are these?

Answer 23

1. Peak shifts

2. Wright’s shifting balance theory

Question 24

How do peak shifts occur?

Answer 24

Mutations in regulatory genes cause major phenotypic effects. These are either deleterious and removed or beneficial, causing organisms to jump to a new optima.

Question 25

What is Wright’s Shifting Balance Theory?

Answer 25

When a subpopulation is exposed to drift, it shifts across the landscape through the trough of an adaptive valley, as reduced genetic diversity produces minimal fitness. The subpop. is then at the base of a new peak and can begin hill-climbing towards new optima.

Question 26

Who critiqued Wright’s Shifting Balance Theory? What did they say?

Answer 26

Coyne et al., 1997

There is support for each stage of the theory independently but no cases in which all three come together to produce an adaptive shift

Question 27

In the Wright Metaphor, evolution is thought to halt at a peak and recommence only under…

Answer 27

changing conditions

This means the Wright Metaphor is insufficient to explain rapid biotic changes that are continually evolving

Question 28

Who put forward the RQ hypothesis and when?

Answer 28

Leigh Van Valen in 1973

Question 29

What is the RQ hypothesis?

Answer 29

That adaptation is driven by biological factors in a cyclical process that requires perpetual change in all players to ensure their survival

Question 30

The RQ hypothesis is named after a quote from Alic Through The Looking Glass by Lewis Carroll, when the Red Queen says ‘…it takes all the running you can do to stay in the same place…’, what does this mean in terms of evolution?

Answer 30

Players are in a constant evolutionary arms race, evolving to out-compete each other but remaining constantly locked in competition

Question 31

What is Fluctuating Red Queen (FRQ)?

Answer 31

Fluctuating selection drives continuous, time-lagged oscillations in allele frequency in both parties

Question 32

Explain FRQ in terms of exploiters and their victims.

Answer 32

Exploiters track the common genotype, allowing the rare genotype to become common, then the exploiter shifts its preference to the new common genotype, and the cycle continues

Question 33

Give a referenced example of FRQ in snails.

Answer 33

Jokela et al., 2009

P. antipodarum snails are hosts for nematodes. Snails exist in mixed sexual and asexual pops.
Sexual populations remained stable, whilst asexual populations did not. Common clonal types became more susceptible to parasites and were eventually driven to extinction, whilst rare clonal types became more prevalent as common types declined.

Question 34

Give a referenced example of FRC in worms.

Answer 34

Morran et al., 2011

C. elegans worms are hosts for parasite S. marcescens. Mating system was genetically manipulated so that worms existed in either sexual, self-fertilising or mixed populations.
Parasite introduction = self-fertilising populations driven to extinction, whilst sexual populations displayed reciprocal coevolution.

Question 35

Why did sexual populations persist in response to FRC in both Jokela et al. (2009) and Morran et al. (2011)?

Answer 35

Because sex increases variance by recombination, creating new genotypes that have higher fitness than the parents in response to parasite invasion

Question 36

What is Escalatory Red Queen (ERQ)?

Answer 36

Directional selection favours extreme phenotypes, which drives the evolution of an adaptive trait. The traits in both parties exceed in value until a stable equilibrium is reached or one player can no longer compete.

Question 37

Under ERQ what limits coevolution?

Answer 37

When traits become too costly to produce

Question 38

Give an example of EQR between a reptile and an amphibian.

Answer 38

Geffeney et al., 2002

Predator is T. sirtalis (garter snake) and prey is newts of the genus Taricha.
Newts produce tetrodotoxin (TTX) to discourage snakes.
Snakes display toxin resistance.
In areas of high snake resistance newts produce more toxin.

Question 39

Geffeney et al., 2002:

How do garter snakes resist the effects of TTX?

Answer 39

They have developed TTX-resistant sodium channels in their skeletal muscle

Question 40

Give an example of ERQ in bean weevils.

Answer 40

Crudgington et al., 2000

C. maculatus males and females are under SAC.
Males have sclerotic penile spines that break off in female repro tract and injure her. Therefore she cannot mate again for long periods which ensures that the male’s sperm fertilise her eggs. Plus males release chemicals that stimulate female oviposition, which enter her haemolymph more quickly through wounds.
In response females have coevolved the behaviour of kicking males during copulation; this significantly reduces male copulation time and damage to repro tract.
Spines/kicking phenotypes have increased over time.

Question 41

So in conclusion, the Wright metaphor is better for studying…

Answer 41

slower, abiotic changes that stop/start

Question 42

So in conclusion, RQD are more useful for studying…

Answer 42

rapid, biotic changes that involved cyclical or escalatory interactions between two players

Question 43

Who described ERQ dynamics in water striders?

Answer 43

Perry and Rowe, 2011

Clasps in males and shields in females

Question 44

Who described the genetic robustness of viruses on the Wright Landscape? What did they say?

Answer 44

Lauring et al., 2013

Viruses have v. high mutation rate thus are inherently robust to mutations.
Their fitness topology is therefore a series of low hills, as when selection knocks a genotype away from one optimum it is likely to land on another peak.