Lecture 9 - selection is change in gene frequency

Question 1

How is gene selection the engine of Natural Selection?

Answer 1

• The evolution of altruistic behaviour
• Kin selection
• Selfish genetics

Question 2

What is altruistic behaviour?

Answer 2

does something for the benefit of another

Question 3

Describe how alarm calls in Belding’s ground squirrels are an example of altruistic behaviour

Answer 3

• give alarm calls when a predator approaches - an altruistic action
• Sherman & colleagues studied the evolution of alarm calls in groups
• the LIKELIHOOD of an individual giving an alarm call was related to whether the group contains relatives or not.
• tested empirically by putting individuals into different groups
• if the individual was in a group with few relatives, less likely to give alarm call

Question 4

Why are alarm calls in Belding’s ground squirrels, as an example of altruistic behaviour, hard to explain evolutionarily?

Answer 4

as it doesn’t benefit the individual - more vulnerable to predation

Question 5

How are helpers at nest e.g. Florida Scrub Jay an example of altruistic behaviour?

Answer 5

• in most bird fledglings leave the nest when they are able to fly
• in some the chicks stay at the next
• these sacrifice their own reproduction
• helps their parents to raise more broods

Question 6

Why is altruistic behaviour an evolutionary conundrum?

Answer 6

• altruistic behaviour potentially challenges evolutionary ideas
• selection favours the spread the genes if they code for traits that increase fitness
• a gene that codes for altruistic behaviour will surely help the other genes

Question 7

What is Kin selection?

Answer 7

• explanation for altruistic behaviour
• altruistic behaviour increases the survival & reproduction of other individuals
• i.e. increases the fitness of others
• those other individuals are kin (relatives)
• i.e. possess the same genes
• altruistic genes increase the rate of spread of themselves via relatives

Question 8

Define Kin selection

Answer 8

an altruistic action will be favoured if it benefits kin

Question 9

When do altruistic actions evolve?

Answer 9

when (r x b) > c

r = related of target individual
b = benefit to target
c = cost to giver

Question 10

What is relatedness?

Answer 10

relatedness is the proportion of genes shared because of common ancestry

• measured between 0-1

Question 11

Describe how related we are to relatives

Answer 11

Offspring - parent = 0.5
Sibling - sibling = 0.5
Grandparent - grandchild = 0.25
Cousin - cousin = 0.125

Question 12

What does r stand for in the equation for relatedness?

Answer 12

• relatedness of target individual
• probability that a member of kin contains a gene for an altruistic act

Question 13

What does b stand for in the equation for relatedness?

Answer 13

• benefit to target
• is number of extra copies of the gene that act yields

Question 14

What does c stand for in the equation for relatedness?

Answer 14

• cost to giver in terms of lost number of copies of the gene that individual produces

Question 15

What are selfish genes?

Answer 15

• a gene will spread in a population if it causes more copies of itself to be produced
• kin selection is the most obvious example
• but kin selection not strictly the only mechanism

Question 16

Why are genes selfish?

Answer 16

anything that a gene can do to favour its own spread at the expense of others will be favoured by selection
- altruism is only favoured by evolution if it increases the rate of spread of a gene
- hence the term ‘selfish’
- the individual doesn’t play any role in this
- it is just the outcome for the gene that is important

Question 17

How does selection act on genes?

Answer 17

• genes are contained with individuals
• individuals actually reproduce and die
• our selfish genetic considerations are more important

Question 18

What is an example of where selection acts on genes?

Answer 18

green beard genes
- under kin selection it pays to be altruistic towards kin - you known the likelihood that they share genes
- an altruism gene that is GENETICALLY LINKED to an obvious phenotype will spread if possessors are altruistic towards each other

• doesn’t require relatedness
• evolution of genes in a population just be cause of a phenotype, not based in relatedness

Question 19

Why are green beard examples important?

Answer 19

• these are important because they demonstrate the principle of gene level selection

Question 20

Describe green-beard effects in red fire ants

Answer 20

• all egg-laying queens are Bb
• bb queens die naturally
• BB queens are killed by Bb workers
• use odours to distinguish BB from Bb
• genotype linked to behaviour, hence a green beard effect

This is an example of the green beard principle, as the workers are killing the queen to conserve their genes - if you follow the rules of natural selection, the b allele should be eradicated

Question 21

Describe green-beard examples in blue-beards in lizards

Answer 21

• unrelated male lizards from partnerships to protect territories
• they have blue throats
• under some circumstances one of the males may have no offspring = “true altruism”
• genes for throat colour & cooperation are linked
• hence a true green-beard effect

Question 22

What is the green-beard effect?

Answer 22

• relatively few examples
• ‘false-beards’ - can easily cheat
• cheating: possesses the green beard but doesn’t reciprocate altruism
• green beards are probably evolutionarily unstable
• kin selection probably more common
• but green beard effect is a logical consequence of gene-level selection
• these are important because they demonstrate the PRINCIPLE of gene level selection

Question 23

What are the selfish genetic elements?

Answer 23

• example that gene-selection is more important that individual selection
• gene level selection affects evolution of genetic material
• e.g. meiotic drive

Question 24

What is an example of selfish genes in drosophila?

Answer 24

• segregation disorder (sd)
• ‘sd’ alleles found in 90% proportions compared to wild type (10%) - example of selfish genetics