Asymmetry in parental investment
between male and females:
Before fertilization:
Asymmetry in size and number of gametes,
and in the rate that gametes are released.
MALES
FEMALES
•Small gametes
•Large numbers
•Energetically cheap
•Large gametes
•Small numbers
•Energetically costly
Asymmetry in parental investment
between male and females:
Before fertilization:
Asymmetry in size and number of gametes,
and in the rate that gametes are released.
After fertilization:
Asymmetry in incubation (some birds),
in gestation (mammals), and in care and
feeding of young (mammals, some birds)
Because the fastest rate that a female can
reproduce is slower than the fastest rate
that a male can reproduce (especially in
birds and mammals)
Females are a scarce resource for males
** Female RS is limited by food, condition.
** Male RS is limited by females.
Parental investment:
Any effort by a parent to increase the
chances of survival of an existing
offspring at the expense of the
parent’s ability to produce
future offspring.
Parental investment involves a
trade-off between current and
future offspring.
For females:
•Few gametes
•Each mating is a large
% of lifetime RS
•RS depends on the
% of offspring
raised to maturity
For males:
•Many gametes
•Each mating is a small
% of lifetime RS
•RS depends on the
number of females
fertilized
Females put most of their reproductive
effort into parental effort, while males
put theirs into mating effort.
Female reproductive success depends
on nutrition
Male reproductive success depends
on access to females
Mating systems and parental care
in birds and mammals
Mammals: Internal gestation, lactation.
- Over 90% of species are polygynous.
- Male parental care is rare.
Birds: Eggs must be incubated, chicks must
be fed (in most species).
- Over 90% of species are monogamous.
- Male parental care is often essential.
Maximum number of offspring produced
during lifetime:
Elephant seal
Red deer
Human
Kittiwake gull
Male
Female
100
8
24
14
>2000
30
26
28
Parental care in fish
Male
care
Female
care
Both
care
External
fertilization
28
6
8
Internal
fertilization
2
10
0
Factors that influence male parental care:
1.
External vs. internal fertilization/gestation
2.
How effective is care by 1 or 2 parents?
3.
Can a deserting male improve his RS?
4.
Paternal certainty