costs of reproduction. costs for females a. gestational costs –
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COSTS OF REPRODUCTION
COSTS FOR FEMALES
A. Gestational Costs–
0 18 36
Kc
al/
da
y/i
nd
ivid
ua
l
0
10
20
30
40
50Caloric Intake of Bank Voles
Source: Flowerdew (1987, Mammals: their reproductive biology and population ecology)
Breeding female
Non-breeding female
Pregnancy Lactation
COSTS FOR FEMALESB. Lactational Costs
– Compared with pregnancy costs
80%
200+%
COSTS FOR FEMALESB. Lactational Costs
– Effect of litter size
Week of Lactation
0 1 2 3 4 5
Mu
ltip
les
of
Ma
inte
na
nc
e
0
1
2
3
4
0
1
2
3
4Lactation Costs for Cats
5 Kittens
3 Kittens
2 Kittens
Maintenance needs
2x
COSTS FOR FEMALES
C. Variation Due to Sex of Offspring– Polygyny and sexual dimorphism
COSTS FOR FEMALES
COSTS FOR FEMALES
C. Variation Due to Sex of Offspring
COSTS FOR FEMALESC. Variation Due to Sex of Offspring
– Bighorn sheep:
Su
rviv
al o
f S
ec
on
d-y
ea
r L
am
bs
(%
)
0
10
20
30
40
50
60
70
Male Female
Sex of First-year Lamb
Source: Berube et al. (1996, Behav.Ecol. 7:60-68)
COSTS FOR FEMALESC. Variation Due to Sex of Offspring
– Bighorn sheep:
COSTS FOR MALES
A. Behavioral– Increased
movements during breeding season
COSTS FOR MALES
A. Behavioral– Increased scent
marking during breeding season
COSTS FOR MALES
A. Behavioral– Costs of fighting
• red deer – 13-29% of mortality
• mule deer – 19% injury
Adult Mass (kg)
0 100 200 300 400 500
% A
bo
ve
Ma
inte
na
nc
e
0
30
60
90
120
0
30
60
90
120
Relative proteincost
Relative energycost
Costs of Antlers in Deer
COSTS FOR MALES
B. Morphological– antler growth
COSTS FOR MALES
C. Physiological– Example: Brown
antechinus
COSTS FOR MALESC. Physiological
– Brown antechinus males
COSTS FOR MALES
C. Physiological– Example: Brown antechinus
COSTS COMMON TO BOTH SEXES
The cost of poor mate choice inbreeding immunodeficiencies lowered reproductive success
CUTTING REPRODUCTIVE COSTS: SEX RATIO VARIATION
A. Theories for Adjusting Sex Ratios at Birth– Variation in reproductive success of
males and females
(Trivers-Willard hypothesis)
CUTTING REPRODUCTIVE COSTS: SEX RATIO VARIATION
A. Theories for Adjusting Sex Ratios at Birth• Predictions of Trivers-Willard for
polygynous species:
CUTTING REPRODUCTIVE COSTS: SEX RATIO VARIATION
A. Theories for Adjusting Sex Ratios at Birth– Local resource competition
• In primates:– inheritance of female dominance, so …
…male reproductive success is not closely tied to maternal investment
Mandrill
Japanese macaques
Proboscis monkeys
CUTTING REPRODUCTIVE COSTS: SEX RATIO VARIATION
A. Theories for Adjusting Sex Ratios at Birth– Local resource competition
• Predictions:– produce philopatric sex if resources
plentiful– only dominant females produce
philopatric sex if food scarce
Days Before or After Ovulation
-10 -8 -6 -4 -2 0 2 4
Pe
rce
nt
of
Ma
les
30
40
50
60
70
30
40
50
60
70Sex Determination in Humans
Femalebias
Male bias Malebias
CUTTING REPRODUCTIVE COSTS: SEX RATIO VARIATION
B. Potential Causes– Timing of insemination
CUTTING REPRODUCTIVE COSTS: SEX RATIO VARIATION
B. Potential Causes– Sperm selection in females
Production of leukocytes
CUTTING REPRODUCTIVE COSTS: SEX RATIO VARIATION
B. Potential Causes– Sperm selection in males
CUTTING COSTS: COOPERATIVE BREEDING
A. Carnivores• biparental or
communal care• higher milk
production• increased
postnatal growth rates
CUTTING COSTS: COOPERATIVE BREEDING
B. Primates (marmosets)• elevated growth rates• reduced intervals
between births
CUTTING COSTS: COOPERATIVE BREEDING
C. Rodents (prairie voles)• older juvenile
helpers• increased weight at
weaning• shorter time to eye
opening
CUTTING COSTS: INFANTICIDE AS A REPRODUCTIVE STRATEGY
A. An Evolutionary Perspective– Males safeguard paternity– Males increase offspring sired– Females reduce losses
Hanuman langurs
CUTTING COSTS: INFANTICIDE AS A REPRODUCTIVE STRATEGYB. Removing the Log from Our Own Eye
– Darwin on infanticide in humans– Infanticide in societies
• hunter-gatherers• ancient Greece• 18th century Europe and bed deaths• girls in colonial America• girls in India, China