Parental Care

So far …

Mates have been secured

Rules of the particular mating system have been exercised

Offspring to care for

What are the behavioural and evolutionary rules for raising offspring?

Relationship between mating systems and parenting

1. Monogamy - both male and female participate in rearing

e.g. trumpeter swan

Relationship between mating systems and parenting

2. Polygyny - one male, several females

- usually the female provides care

Relationship between mating systems and parenting

3. Polyandry - one female, several males

- usually the male provides care

-Wilson’s phalarope

Relationship between mating systems and parenting

3. Polygynandry - promiscuous

- either sex could provide parental care

Relationship between mating systems and parenting

Phylogenetically

Gross and Sargeant ‘85 - Survey of Teleost fish

Teleosts

79% - no parental care21% parental care

Two parents>75%

One parent <25%

Internal fertilizer External fertilizer

86% female 14% male 30% female 70% male

What governs which sex should invest?

1. Anisogamy

- female has already made greater investment

2. Confidence in parentage

-species with internal fertilization

-male should be inclined to desert

-female should be inclined to care

3. Association with embryo

- sex most closely associated with embryo should offer care

Parental investment

Any investment in an offspring that increases its chances of survival and reproduction at the expense of the parents’ ability to invest in other offspring

Parental investment

Temporal component

Cumulative investment

Territory Mating/egg laying

Incubation Feeding Fledging

MALE

FEMALE

Parental investment

Temptation to desert

Cumulative investment

Territory Mating/egg laying

Incubation Feeding Fledging

MALE

FEMALE

Parental investment

Any investment in an offspring that increases its chances of survival and reproduction at the expense of the parents’ ability to invest in other offspring

Parental investment

Rhesus monkeys

% time in contact

Weeks10 20 30

% timerejected

Parental investment

Budgies

Log feeding rate

Offspring weight

Parental investment

Budgies

BeggingRate

Female alone With male

Parent offspring conflict

At some point, the parent-offspring relationship is terminated

Why and who determines this?

Parent offspring conflict

Trivers

- looked at benefit/cost ratio to parent

Benefit:Gain in survivorship from investing in offspring

Cost:Inability to invest in other offspring

Parent offspring conflict

Trivers

5

4

3

2

1

0.5

0.25

B/Cratio

TimeP O

P OTime of conflict

Parent offspring conflict

Conflict during infancy

Benefit orCost

Level of Parental Investment

1/2 Cost

Maximum benefit for offspring

Maximum reproductive success for parent

Sibling rivalry

Corollary of parent/offspring investment

-any offspring more interested in its own survival more than in its siblings’ survival

- if any siblings benefit:cost ratio is <0.5 - conflict

rsiblings = 0.5

Sibling rivalry

Mock and Parker (1997)

-HIERARCHY MODEL

Total amount of food brought by parents

Sibling rivalry

Does this model explain observations on sibling rivalry?

Cattle egrets

Sibling rivalry

Does this model explain observations on sibling rivalry?

Cattle egrets

Early Mid Late

% share

Sibling rivalry

Great Blue Heron

Weight at day 14

1,2 3 Lost sib4

No loss5

Chick number

Parent Offspring Conflict in Utero

Haig (‘93)

-mother - selected to limit nutrient transfer

- fetus - selected to increase nutrient transfer

Parent Offspring Conflict in Utero

Haig (‘93)

Fetal cells migrate to endometrium

Fetal cells make constriction of arteries more difficult

Benefits to fetusa. hormone release into female’s bloodb. nutrients under fetal control