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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
