Lecture 9 - selection is change in gene frequency Flashcards
How is gene selection the engine of Natural Selection?
- The evolution of altruistic behaviour
- Kin selection
- Selfish genetics
What is altruistic behaviour?
does something for the benefit of another
Describe how alarm calls in Belding’s ground squirrels are an example of altruistic behaviour
- 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
Why are alarm calls in Belding’s ground squirrels, as an example of altruistic behaviour, hard to explain evolutionarily?
as it doesn’t benefit the individual - more vulnerable to predation
How are helpers at nest e.g. Florida Scrub Jay an example of altruistic behaviour?
- 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
Why is altruistic behaviour an evolutionary conundrum?
- 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
What is Kin selection?
- 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
Define Kin selection
an altruistic action will be favoured if it benefits kin
When do altruistic actions evolve?
when (r x b) > c
r = related of target individual
b = benefit to target
c = cost to giver
What is relatedness?
relatedness is the proportion of genes shared because of common ancestry
- measured between 0-1
Describe how related we are to relatives
Offspring - parent = 0.5
Sibling - sibling = 0.5
Grandparent - grandchild = 0.25
Cousin - cousin = 0.125
What does r stand for in the equation for relatedness?
- relatedness of target individual
- probability that a member of kin contains a gene for an altruistic act
What does b stand for in the equation for relatedness?
- benefit to target
- is number of extra copies of the gene that act yields
What does c stand for in the equation for relatedness?
- cost to giver in terms of lost number of copies of the gene that individual produces
What are selfish genes?
- 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
Why are genes selfish?
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
How does selection act on genes?
- genes are contained with individuals
- individuals actually reproduce and die
- our selfish genetic considerations are more important
What is an example of where selection acts on genes?
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
Why are green beard examples important?
- these are important because they demonstrate the principle of gene level selection
Describe green-beard effects in red fire ants
- 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
Describe green-beard examples in blue-beards in lizards
- 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
What is the green-beard effect?
- 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
What are the selfish genetic elements?
- example that gene-selection is more important that individual selection
- gene level selection affects evolution of genetic material
- e.g. meiotic drive
What is an example of selfish genes in drosophila?
- segregation disorder (sd)
- ‘sd’ alleles found in 90% proportions compared to wild type (10%) - example of selfish genetics
