Kin selection nad helpers at the nest

Lecture 2

Way to pass down copies of your genes

• Direct fitness

  • own offspring

• Indirect fitness

  • helping relatives with their offsrping

Most obvious examples of indirect fitness

Sterile worker castes i social insects

• spend entire lives helping queen reproduce

Birds and mammals

• ‘helpers in the nest’

Florida Scrub Jays

Stay with parents and help them raise their broods

2 effects:

• increase success of current brood

• reduce breeders’ effort = increase future success for breeder
  

When to help and when to not?

• Often part of life history

• Help before they find their own territory

• But

• Some are helpers their whole life

Cooperative breeding in birds

Described in 10% of all bird species

Cooperative breeding in mammals

• in taxa where a monogamous pair monopolise the reproduction

  • produce large litters

  • so lots of close relative in the group

    • who can raise the kin

    • e.g meerkats?

Altruism

helping other to raise offsrping at a cost to one’s own personal reproductive success

How can altruism evolve? Hypotheses…

1. Delayed direct fitness benefits

2. Indirect fitness benefits- Kin selection

Hypothesis 1- Direct fitness

• Maintain the group or territory

  • because the helper needs to breed there in the future

• Show Parental quality

  • Better changes of getting a future mate

  • e.g Pied Kingfisher

• Payment to breeders to stay in territory

  • e.g superb fairy wren: get punished if they don’t help

Hypothesis 2- Indirect fitness

Can pass copies of genes indirectly by helping siblings

• Direct= descendent kin

• Indirect = non-descendent kin

Hamilton’s rule

Hamilton’s Rule: r_AB

Probability individual B has a copy of a gene in individual A by direct descent

• prob they share copies of genes above the background level

  • background level: because they are the same species

Calculating r from pedigree

r= 0 between random individuals

r=1 between clones

• each line = meiosis

  • so x 0.5

• 0.5 to the power of how many links there are in a path from one thing to the other

• Sum of all the paths

Matching r of descendant to non-descendent

Can get just as much genetic benefit from helping full siblings to having your own kids

Combining both direct and indirect fitness

= Inclusive fitness

Hamilton’s rule

• If a Donor sacrifices C offspring

• Recipient gains an additional B offspring

• altruism is favoured when

  • rB - C> 0

    • the indirect benefits to the donor (rB) is greater than the costs to the donor

Testing the theory: Mate sharing by Males example 1

Tasmanian native hens

• breed as pairs or two male trios (With brothers)

  • one of the brothers in dominant

  • But: allows the his brother to copulate

• In a trio: there are overall more offspring

Is this an example of kin selected altruism?

The payoffs from dominant male’s alternative choices

• Assuming equal share of matings

If dominant male is altruistic:

• Benefit to subordinate male= 1/2N₂ -0

• cost to dominant male = N₁ -1/2N₂

Apply rB-C>0

• If r=0, altruistic is ½ N₂ > N₁

  • (4.8<6.6 → NOT altruistic payoff₎

• if r=1.2 altruistic if 3/4N₂ >N₁₎

  • 7.2>6.6 so dominant male gains a larger genetic profti from altruism

Testing the theory: Mate sharing by Males example 2

Human fraternal polyandry in Tibet

• Wife with several brothers fro husbands

• Under harsh conditions

  • may pay for dominant male to cooperate with younger brothers

    • increases productivity

    • increases no. offspring

Is this altruism?

Same equations as with hens:

• ¾ N2>N1

• Altruism (just)

Limitations with these studies

1. Details paternity sharing are not yet known

2. Dominant males may not be making the decisions

   • e.g females benefit from increased male help

3. Human societies: culture has an influence

Testing the theory: Seychelles Warblers

• Young stay at home to help their parents to raise further broods

Why?

• habitat saturation

  • not enough free territory for offspring to leave so stay at home and claim indirect benefits

Initially assumed that breeders had full paternity

So the genetic benefit for helping siblings is 0.2 but breding is 0.4

• Then why do they help???

Why do they help if it is less fitness? Hypothesis 1

Ecological constraint

• full haitat with no opportunity to breed

• Test:

  • new islands= no helping at first

  • until fully saturated

BUT: other issues found with DNA profiles

1. high levels of extra group paternity in Seychelles

2. Female helpers often lay eggs in nest

   • so direct is MORE important than indirect for female helpers especially

So, new views on why helping happens

1. A decision favoured by kin selection

2. By-product of a provisioning rule

   • selected in the context of parental care

View 1: Helping is a decision

• Helpers do not always help

  • vary help depending on chances of relatedness to nestlings

Evidence favours this one more

When are you more likely to help

• If the primary female is still present

  • 85% chance young in nest is from primary female

  • You have 85% shes your mum

  • so, her next offspring are 85% hers

    • Probability helper is related to offspring 0.85 ×0.85= 0.72

Less reliable cue

Continued presence of primary male

• Only 60% of chicks are the father’s

• Prob hes your dad 0.6

• prob hell father the young 0.6

  • Prob they are your sibs: 0.6×0.6= 0.36

So when do helpers actually help more?

Need a reliable cue that they actually are related to the siblings

• best cue is if primary mother still present

Other cues used to ensure relatedness

E.g Long-tailed tits

• cross-fostering experiments

• showed they learn signature calls from provisioning adults

• target these individuals when they go to help them

View 2: provisioning by-product

• When a habitat is full and offspring stay at home

• they will naturally help feed due to begging chicks

  • Beneficial

• But also do this for cuckoo care

  • costly

Therefore not really selected for: just a by-product