Lecture 10b - reproductive conflicts

Question 1

where is conflict seen within families?

Answer 1

Conflict among siblings

Conflict between parents and offspring

Question 2

who came up with the parent-offspring conflict model?

Answer 2

Trivers 1974

Question 3

describe the parent-offspring conflict model

Answer 3

• As a parent the more you invest into your offspring the better their chance of survival - however that has to level off and only reaches a point - survival cant be more than 100%
• Cost also increases the more you invest
• There is conflict over parental investment - offspring should want parents to invest more than parents want to give
• Optimal investment for parent is less than optimum for offspring

Question 4

what does sibling rivalry result from?

Answer 4

Conflict over limited resources

Question 5

what are results of sibling rivalry?

Answer 5

• result is often siblicide, and in some cases cannibalism - could be just from competition

Question 6

2 examples of sibling rivalry

Answer 6

E.g. sand tiger shark - only ever produce a single offspring - largest foetus actually eats it way through siblings in the uterus of the mother
E.g. spadefoot toads - as tadpoles you get cannibal morphs developing which eat their siblings

Question 7

describe sibling rivalry in hyenas?

Answer 7

produce 2 pups at a time - Twin pups are unsupervised in burrows and fight with sharp canines - often one dies
Rivalry is more intense with same sex twins:
Expect: 1 MM : 2MF : 1FF
i.e. 50% same sex twins
Observe: 15% same sex twins
same-sex siblings are future reproductive competitors - pre-emptive strategy to wipe out competition

Question 8

Sibling rivalry has been most intensively studies in birds - give an example

Answer 8

E.g. black eagles - two eggs hatch 3 days apart - but only one survives
Older chick attacks younger sibling as soon as it hatches
From 199/200 nests in which both eggs hatched, only one survived
= CAINISM

Question 9

what are the 5 characteristics of siblicide?

Answer 9

1) resource competition
2) Monopolisable resources
3) Spatial confinement
4) Weaponry (not essential)
5) Competitive disparities- typically, under parental control e.g. incubating eggs all at the same time would remove size differences

Question 10

give an example of how resource competition affects siblicide

Answer 10

e. g. white-winged chough (Boland et al. 1997)

- no of fledglings survived increased in fed compared to control

Question 11

what are the 2 reasons siblicide occurs?

Answer 11

1) insurance

2) parental optimism

Question 12

describe insurance in terms of siblicide?

Answer 12

only enough resources for one chick, second is produced as insurance against first not surviving

Question 13

describe parental optimism in terms of siblicide?

Answer 13

produce large clutch, in good conditions all will survive, in poor conditions sibling rivalry efficiently reduces the brood size
Brood hierarchy arises from parental strategy to engineer optimal hatching asynchrony - would be annoying to have only produced one and then there was loads of resources - but also annoying to have more than one when food is scarce

Question 14

describe the experiment proving parental optimism?

Answer 14

e. g. cattle egrets - manipulated timer interval between first and second chick hatching
- Looked at survivorship of chicks from 3 different treatments
- Maximum survival excess was achieved with the standard observed hatching interval
- Parents engineer optimum synchrony

Question 15

give an example of sibling rivalry in humans

Answer 15

In humans, sons are costlier to produce… (pre industrial finnish populations- looked at birth records)

• Higher lifetime reproductive success if your older sibling was a sister than if it was a brother

Question 16

describe parent-offspring conflict

Answer 16

• Offspring try to persuade their parents to give them something they don’t necessarily want too - very common e.g. chicks begging, children throwing tantrums

Question 17

describe how parent-offspring conflict in the american coot

Answer 17

• Parental care is essential for survival - 50% of chicks starve
• Parents control who gets food and who doesn’t
• Orange body feathers and and papillae are signals to their parents of the quality of the offspring - did experiment by painting orange on some chicks
• Orange chicks were fed more, grew faster and survived better

Question 18

describe an example of parent-offspring conflict in humans

Answer 18

• Foetal genes are selected to maximise transfer of nutrients to foetus
• Maternal genes are selected not to exceed maternal optimum
• Genetic conflict between mother and foetus

Question 19

what 2 common diseases can foetal manipulation result in

Answer 19

Gestational diabetes - placenta releases human placental lactogen to maintain blood glucose levels, mother increases insulin in response, diabetes occurs if response inadequate
Pre-eclampsia - foetus enhances blood & nutrient flow to placenta by increasing maternal blood pressure, if it goes too high mother & baby’s lives can be threatened

Question 20

what did a study in humans parental investment show?

Answer 20

Parental investment and child development in contemporary British families (Lawson & Mace 2011).
- Showed family size to effect parental care, economic hardship, school tests and height

Question 21

what are families characterised by?

Answer 21

conflict and cooperation