Selfish Genes (Freckleton)

Question 1

Kin Selection

Answer 1

-Kin selection is an explanation for altruistic behaviour; when one individual performs for the benefit of the other, e.g. parent caring for offspring, social cooperation, alarm calls in birds.

An altruistic behaviour will be favoured if it benefits kin, if rb > c, altruistic behaviour happens.
-r=relatedness of target individual/probability that a member of kin contains a gene for an altruistic act. If one parent has copy of gene, 0.5 chance that sibling will have that gene too.

• b=benefit to target/number of extra copies of the gene that the act yields.
• c=cost to giver. Increase in number of copies through reproduction/cost in terms of lost number of copies of the gene that the individual produces. Number of copies of genes lost through completing the act, through loss of fitness.

Kin selection is actually ‘gene selection’: kin selection measures the effects of selection at the level of individual genes.

Question 2

Example of Kin selection

Answer 2

Alarm calls in Belding’s ground squirrels:

• Squirrels give an alarm call when a predator approaches; an altruistic action which alerts the rest of the group.
• Sherman and colleagues studied the evolution of alarm calls in groups and found:
• The likelihood of an individual giving an alarm call was related to whether the group contains relatives or not. If the group contained relatives it was very likely to give an alarm call, if it was in a group with others who weren’t related, much less likely to make call.

-They tested this empirically by putting individuals into different groups

Question 3

Gene Selection

Answer 3

A gene will spread in a population if it causes more copies of itself to be produced. Kin selection is the most obvious, but not the only mechanism. Gives rise to the idea of selfish genes.

Question 4

Why are genes selfish?

Answer 4

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.
• The individual plays no role in this, it is just the outcome for the gene that is important.

Question 5

Gene-level Selection

Answer 5

Genes are contained within individuals, which reproduce and die.
-Selfish genetic consideration are more important at the gene level instead of the individual level.

Question 6

Green Beard genes

Answer 6

(Under kin selection it pays to be altruistic towards kin, you know the likelihood that they share genes. Kinship is an easy way to know if people will have a good chance of sharing genes.)

• An altruism gene that is linked to an obvious phenotype will spread if possessors are altruistic towards each other. It will spread through population of individuals with the phenotype.
• E.g. a green beard signifying that owner possessed a give gene.
• This mechanism doesn’t require relatedness.

Question 7

Green-beard vs kin selection

Answer 7

In green bread, likely to be quite related close to gene loci, but not everywhere. In related individuals, there are likely to share a lot of the same genes.

• Green beard, genes for action and signal are linked, but individuals are unrelated at other loci.
• Kin recognition, genes for action and signal are linked, but individuals are related at all loci.

Question 8

Green beard effects in red fire ants

Answer 8

• All egg laying queens are Bb
• bb queens die naturally but, BB queens are killed by Bb worked.
• Odours are used to distinguish BB from Bb.
• Shows genotype is linked to behaviour, hence a green beard effect.
• Not happening because its good for the colony or the individuals, only for the genes.

Question 9

Green beard effects in lizards

Answer 9

• Unrelated lizards with blue throats form partnerships to protect territories.
• Under some circumstances, one of the males may have no offspring (happens quite often).
• Genes for throat colour and cooperation are linked. Even though no offspring, the altruistic gene is still spreading, as one lizard is helping the other lizard to protect the territory, and therefore enhances the survival chances of offspring.

Question 10

Green-beard effects

Answer 10

False-beards can easily ‘cheat’ - posses the green beard but do not reciprocate altruism, can benefit from possessing the green beard but with none of the cost, this means it is probably evolutionarily unstable.

Question 11

Genes override benefits to individual

Answer 11

• Tazmanian devil facial tumour, quickly spreads and is fatal.
• Spreads in the form of individual cells, not of the host genotype, meaning they are unrecognised by the immune system.
• Essentially another individual, derived from another genotype of tazmanian devils, that knows not to divide into an individual, only when in right place. Genotype threatening the existence of the species.

Question 12

Selection acts on replicators

Answer 12

Selection acts on replicators. These are individual units that replicate themselves. Those that leave most copies are the most successful.

• Species aren’t replicators, don’t get new species by copying another species. Species change and adapt.
• Individuals aren’t replicators either. Genes, not individual.