L13 Kin Selection

Question 1

Classifying social behaviours

Answer 1

see onenote slides

• behaviour causes a change in fitness
• altruism
• mutualism
• spite
• selfishness

Question 2

Altruism in nature

Answer 2

• parental care
• cleaner fish
• bee’s suicide gene when it stings something
• cooperative hunting in primates

Question 3

Inclusive fitness

Answer 3

See onenote diagram

inclusive fitness = direct fitness + indirect fitness

r = coefficient of relatedness

Question 4

What is relatedness?

Answer 4

r = probability that homologous alleles present in different in individuals are “identical by descent”
- it measures the genetic similarity between two entities (e.g. individuals or loci), relative to the average similarity of two randomly selected entities

Question 5

How to measure relatedness?

Answer 5

2 common methods:

1. pedigree relatedness
2. regression relatedness

Question 6

Pedigree relatedness

Answer 6

• an approximation calculated from a pedigree
• ranges from 0 to 1
• calculate by looking at a family tree of the two organisms
• real pedigrees are complex and sometimes hard to measure, older common ancestors missing
• meiosis is like a lottery e.g. full siblings have an average of 50% identical alleles
• helps us make predictions from kin selection theory

Question 7

Finding pedigree relatedness

Answer 7

See onenote diagram

- Relies on how meiosis randomly passes down alleles from the parents to the offspring

Question 8

Regression relatedness

Answer 8

• genetic similarity of a pair of individuals relative to the expectation of a random pair
• calculated from molecular markers using algorithms
• ranges from -1 to 1
• 1 means the individuals are genetically identical
• 0 means that the pair share an average number of alleles
• <0 means below-average number of alleles shared (of randomly mixed average pair)
• regression relatedness is great in the real world when we don’t know the full pedigree

Question 9

Hamilton’s Rule

Answer 9

see onenote slides

• an allele that causes a behaviour that increases the fitness of the actor or others carrying the same allele should be favoured by selection
• even if the allele reduces the actor’s direct fitness, it can spread if it increases the actor’s indirect fitness (if it compensates for your loss of direct fitness)
• can explain the evolution of altruism

rB - C > 0
r = relatedness
B = benefit to the recipient (measured as the number of extra offspring produced by the recipient as a result of the behaviour)
C = cost to the actor (measured as the number of offspring lost by the actor as a measure of performing the behaviour)

Question 10

rB - C > 0

Answer 10

See onenote slides

- Use Hamilton’s rule to predict if altruistic behaviour is favoured, if it is favoured then the inequality is satisfied

Question 11

Testing hamilton’s idea

Answer 11

Hamilton’s rule predicts that organisms should evolve to be more altruistic when:

• they are interacting with close relatives (r)
• their actions are useful to the other individual (B)
• their actions are not too costly (C)

Question 12

Testing hamilton’s idea - parental care

Answer 12

• offspring inherit the “caring alleles” so parental care can evolve via kin selection
• mean relatedness to social offspring is lower for males than females in some species, possibly explaining the rarity of male parental care (dad’s usually less sure that the kids are actually his)

Question 13

How do organisms identify kin?

Answer 13

• Hamilton’s rule shows that altruistic behaviour is advantageous provided that it is directed at other altruists often enough
• Hamilton proposed that organisms should evolve recognition systems to help direct their social behaviour

Kin recognition system
- Altruistic behaviour often directed to individuals with the same alleles as you

Question 14

Environmental cues

Answer 14

• many organisms cannot recognise kin but instead “guesstimate” using simple cues
  e. g. if we grew up together we’re probably related, if it’s in my nest and makes the right sounds it must be my baby

Natural selection doesn’t find the BEST solution but finds the most adequate solution given the resources

Question 15

The “armpit” effect

Answer 15

• be nice to individuals that smell like you
• mammalian MHC and MUP
• insect cuticular hydrocarbons (CHCs)

Ants from the same nests have more similar chemicals than with ants from other nests, partly genetically coded and due to the environment

Mice can identify genetic similarity by smelling MUP - a polymorphic protein

Question 16

Genetic recognition loci

Answer 16

• some organisms have simple genetic matching systems where individuals cooperate with others that have the same allele as them
• precursor to self/non-self recognition immune system
• cell surface receptors for recognition in anemone

e.g. slime moulds, sea squirts

Question 17

Green beards

Answer 17

see onenote slides

• initially a though experiment by Hamilton
• its point is that having the same allele at the relevant locus is the point, not relatedness per se

What if a gene had three effects:

• producing a detectable cue (e.g. a green beard)
• causing individuals to prefer others with the same cue
• causing a social behaviour

Question 18

Multi-level selection theory

Answer 18

• aka “new group selection”
• cooperative groups might give rise to more new groups than non-cooperative group
• controversial, some say it’s mathematically identical to kin selection theory

Selection within an individual e.g. TE increase their frequency within the genome in comparison to other genes

Some groups fitter than other groups e.g. some beehives leave more descendent bees than other hives