Female enforcement
Conflict of interests between the sexes regarding
care of offspring, opportunities for additional matings
Female untethered
Female tethered
burying beetle
< 6 min
> 6 min
Duration of male
pheromone emission Extra-pair copulations
-1
.0
0.9
1
-0
.90
0.8
1
-0
.80
0.7
1
-0
.70
0.6
1
-0
.60
0.5
1
-0
.50
0.4
1
-0
.40
0.3
1
-0
.30
0.2
1
0.1
1
0.0
superb fairy wren
-0
.20
9
8
7
6
5
4
3
2
1
0
-0
.10
tree swallow
Number of broods
In some species, >50% offspring are extra-pair young
Proportion of extra-pair young (EPY)
50-90% EPY (avg. 78%) Why do females solicit EPCs?
Material benefits?
Adelie penguins get
rocks from EPC partners Why do females solicit EPCs?
Material benefits?
scorpionfly
• EPCs are less “institutionalized”
version of polyandry
• Many of the same benefits apply Why do females solicit EPCs?
Male defense
…against nest predators
red-winged blackbird
32% predation on females with EPY
54% predation on females with no EPY
…against infanticidal males
Hanuman langur
Females may mate often
to confuse paternity Why do females solicit EPCs?
Genetic benefits
– Guard against poor sperm quality of mate
pseudoscorpion Why do females solicit EPCs?
Genetic benefits
– Guard against poor sperm quality of mate
– Increase genetic diversity of offspring
blue tit Why do females solicit EPCs?
Genetic benefits
– Guard against poor sperm quality of mate
– Increase genetic diversity of offspring
– Mate with genetically superior male
bluethroat EPCs in humans
Population
southern Africa (!Kung)
% nonpaternity
2
rural Michigan, USA
~10
Munich and Copenhagen
>10
Italy
13.2
India
15.3
urban Michigan, USA
20.1
Liverpool, UK
20-30
Mating Systems and Parental Investment Part 4
of 9
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