Mating Systems
Psychology 3107
Introduction
For the most part, males’ involvement in
mating, well, ends after the mating
Females pay for the mating a lot more
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Physiologically
Post birth/hatch care
Therefore, we should expect Polygyny
where males have more than one mate
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Male variance > female variance
Polygyny
There are several
theories about
polygyny
Resource defense
polygyny
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Male defends some
good resource
Example,
hummingbirds
The resource is some
nectar giving flower
Hummingbirds
Male sets up territory
Excludes other males
Basically, the male exchanges letting
females feed in exchange for copulations
Sort of like nuptial gifts in some sinsects,
but the ‘gift’ is stationary
Females then set up breeding territory
withing male’s teritorry
Polygyny Threshold
Polygyny may occur
when the ‘polygyny
threshold’ is crossed
Example here is
migratory songbirds
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Males arrive, set up
territories
Females choose
mates
Polygyny Threshold
When differences in qualities of available
territories crosses the polygyny threshold,
then polygyny results

It is more profitable for the female to become
a secondary female with a high end male,
then a primary femle with a mid range
What about monogamy
Monogamy should happen if:

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Curves are far apart
Curves are flat
In other words, little variation in quality of males
and their territories
Verner and Wilson did a really cool study
that looked at these ideas
Verner and Wilson
Marsh birds
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Quality varies greatly
vs
Non Marsh birds
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Not so much variation
Prediction is that there should be much
more monogamy in non marsh living
songbirds
So, what happened
Marsh species  44 % are polygynous
Non Marsh
 2 % are polygynous
You can also get female defense polygyny
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Males basically guard the females
Good example here is in Bison
But you said we’d talk about
monogamy…
OK, OK……
When should mongamy happen?
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When the young are in need of lots of
parental care
When Territories or resources are poor
When females actually enforce it!
Some ‘monogamous’ species aren’t…..
Extra Pair Copulations
Happens a lot in birds
Ummm, happens a lot
in people
‘sperm competition’
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Usually when female
is unguarded or when
male can get away
with it…..
Sperm Wars
Polyandry
One female, many
males
Exceedingly rare
Usually only happens
when there is
complete sex role
reversal
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Sea horses
Spotted sandpipers
Conclusions
Many theories as to why different animals
have different mating systems
Polygyny is by far the most common
When you think about it, the system
correlates nicely with the gametes!