Lecture 6: Parental Care & Kinship - Costs vs. Benefits
Sexual Conflict over PARENTAL CARE
[Parental Care in the Magnificent Frigatebird]
Parental care = a cooperative venture between a male and a female in many socially
Care = costly; so sexual conflict arises between the parents about how much effort
they should invest into rearing their young.
The sexual conflict over care is most apparent when one parent abandons the
brood before the offspring are independent.
The deserted parent has three options:
(1) desert the brood because a single parent is unable to raise the young on its own;
(2) continue care provision at the same level as during biparental care, and thus do not
compensate for the absence of mate;
(3) increase care and compensate partially or totally.
During biparental care, females fed the chick more often than the males. After their
mate deserted, the females nearly doubled their feeding rate and thus, fully
compensated for the lost care.
Growth rates of chicks provided with biparental and female-only care did not differ.
Females may withhold care during biparental care to manoeuvre their mates into
prolonged care provision. A female only provides at her full capacity once her mate
What IS “Parental Care”?
Behaviour by parent which increases OFFSPRING’S fitness (and would not occur in
absence of offspring).
MODES of Parental Care
Maintenance (grooming, heat, gas exchange, defense against disease etc)
Teaching WHY Care? (at all …)
It all comes down to benefits/costs
PRECOCIAL young: species in which the young are relatively mature and mobile
from the moment of birth or hatching; e.g. fish, insects, spiders
ALTRICIAL young: where the young are born or hatched helpless; e.g. birds,
canines, felines, primates
Expect parental care to EVOLVE when …there is a high benefit/low cost to it!
Selection pressure from the environment
K-selection (stable environments):
Constant, predictable environment
Individuals are larger, longer lifespan… population at capacity
Selection Pressure: Intense INTRAspecific competition
Strategy: QUALITY (few, but well-prepared offspring –strength, knowledge,
Parental care has HIGH BENEFIT
r-selection (unstable environments):
Uncertain, variable environment
Low survivorship, short lifespan
Selection Pressure: unpredictable environment, predation
Strategy: QUANTITY (many cheap offspring – some will survive by chance
Parental care has LOW BENEFIT; therefore, little parental care!
TYPES of Care (Systems)
1. NO Parental Care; e.g. many invertebrates, some fish, reptiles & amphibians
2. UNIparental Care aka ONE PARENT; e.g. (usually female) e.g. many mammals,
some invertebrates, fish, reptiles, amphibians & birds
3. BIparental Care aka BOTH PARENTS; e.g. many birds, some mammals, few fish
WILLIAM’S PRINCIPAL: Investment in the present comes at the COST of
investment in the FUTURE
LIFETIME REPRODUCTIVE SUCCESS (LRS) depends on: 1. Present Success (P); P is a function of what you are giving to your present
offspring:“Reproductive Effort” (RE)
2. Future Success (F); F is a function of what you have to give your future
offspring (your own growth and survival): “Somatic Effort” (SE)
3. LRS = P(RE) + F(SE); you want to MAXIMIZE your LRS!
As RE = SE
HOW MUCH Care?