inclusive fitness (3)
relatedness self to:
- sibling: 1/2
- niece/nephew: 1/4
- cousin: 1/8
Hamilton’s rule (3)
- a gene that causes an individual to help another at a cost to itself should spread when C < B*r
- C < B*r = cost to actor < benefit to recipient * relatedness of actor to recipient
- an individual can gain “inclusive fitness” by helping genetic relatives
parent-offspring conflict (4)
asymmetrical relatedness between parents and offspring
- offspring related to themselves by r = 1
- parents related to offspring by r = 1/2
- parents equally related to all offspring and should equalize investment
- siblings related by 1 to themselves, 1/2 to siblings, and 1/4 to half-siblings
reasons for parent-offspring conflict (3)
- there must be a cost to the parent providing more care
- there must be a benefit to the offspring receiving care
- there must be diminishing returns on investment
parent-offspring conflict: effects of diminishing returns of investment (2)
- mother does better by switching care to second offspring (mom equally related to both offspring)
- offspring 1 wants more investment for itself
parent-offspring conflict: conflict of interests (3)
- each offspring wants more than its fair share of resources
- each offspring ‘disagrees’ with its parent about the value of other offspring
- offspring may perform costly behaviours (crying, tantrums) to manipulate parents and elicit extra care
parent-offspring conflict: types of conflict (3)
- conflict over amount of investment
- conflict over termination of investing
- conflict over behaviours of offspring towards siblings and other relatives
parent-offspring conflict: conflict over amount of investment(4)
- benefit to current offspring fitness have diminishing effects
- cost of future offspring fitness to parent increase linearly
- cost of future offspring fitness to current offspring increase at 1/2 the rate of the parent
- result: offspring maximize fitness at a greater level of parental investment than is optimum for the parent
parent-offspring conflict: examples of maternal-embryo conflict (2)
- conflict over implantation
- conflict over food supply
parent-offspring conflict: conflict over implantation (3)
- mother abort embryos with chromosomal abnormalities
- embryos produce a hormone to implant/maintain pregnancy
- morning sickness might be a side effect
parent-offspring conflict: conflict over food supply (2)
- embryos produce substance to increase food supply to the fetus by constricting mother’s arteries
- leads to high blood pressure in the mother
parent-offspring conflict: prediction for conflict vs mating system (2)
conflict should be greater when offspring are sired by multiple fathers
- cost of losing any offspring is equal for parent (C)
- cost of losing a sibling is halved (1/2 C)
- cost of losing half-sibling is quartered (1/4 C)
result in greater investment in offspring that are less related to their siblings
parent-offspring conflict: conflict over termination of investment (3)
- parent should end investment when B/C = 1, whereas offspring will demand investment until B/C = 1/2
- parent and offspring stop investment at net fitness benefit peaks, but offspring has later peak
- period of conflict: intervening period where offspring continues to demand investment
parent-offspring conflict: reflection of conflict of termination of investment (3)
attempts by the offspring to elicit more care than parent is prepared to give:
- crying
- regression (behaving younger than actual age)
- temper tantrums
parent-offspring conflict: termination of conflict
- humans
in humans, culture plays a significant role in termination of conflict:
- Bofi farmers wean children abruptly and children exhibit high levels of fussing and crying
- Bofi foragers nurse children longer and children exhibit no marked signs of distress
parent-offspring conflict: conflict over behaviour to siblings and other relatives (2)
- parents will encourage children to value their siblings more than children are naturally inclined to
- parents will tend to punish conflict between siblings and reward cooperation
how are conflicts resolved (2)
- if mom has total control, she can do what is best for her and there is not really conflict
- mothers have less than total control if they respond to signals from offspring`
honest signally theory
- benefit of signalling (more care) greater for individuals in poor condition than for individuals in good condition
- honest signallers pay a cost, but get a sizeable benefit
- cheaters experience net loos
honest signalling theory: why does cheaters experience net loss (2)
- the cost of signalling is high and the benefit of more care is low due to diminishing returns
- they take resources away from siblings, lowering their own fitness
why should a mother respond to offspring signalling (2)
- benefit
- possible cost
- conflict is resolved as is best for mom during honest signalling because mother gets information about offspring condition
- possible cost: cost to offspring to signal (energetic costs, predation risks)
competitive escalation (2)
- begging rate between siblings increases to match one another
- does not necessarily reflect actual needs, but the competition to be heard
