Mating Systems
ZOL 313
June 11, 2008
Mating Systems
Objectives
1. Be able to characterize a given mating system as
monogamy, polygyny, or polyandry.
2. Understand how differences in the distribution of
females and resources lead to different types of
polygyny.
3. Become familiar with hypotheses about the adaptive
value of monogamy and polyandry and be able to
generate hypotheses and predictions.
ZOL 313
June 11, 2008
Types of Mating Systems
1. Monogamy: One male mates with
2. Polygamy: One gender has multiple partners of the other gender.
A. Polygyny:
One male mates with
B. Polyandry:
One female mates with
Polygyny
Most common mating system
Types of Polygyny:
1. Female defense polygyny
2. Resource defense polygyny
3. Scramble competition polygyny
4. Lek polygyny
The spatial distribution of _________ and __________
determines what type of polygyny a species will have.
Polygyny
Female defense polygyny: One male directly defends several females.
Occurs when:
Example: Yellowbellied marmot
females live in groups
of female relatives,
one male will defend a
group of females from
other males.
Prediction:
Polygyny
Resource defense polygyny: One male acquires several mates that are
attracted to resources he controls.
Occurs when:
What types of resources might males defend?
Example: In an African cichlid fish, territorial males bring shells to their
middens that females use as nest sites.
Polygyny
Scramble competition polygyny: One male acquires several widely
scattered mates by finding them before other males do.
Occurs when:
Example: Male ground squirrels have to search widely
for females who are only receptive for 4-5 hours during
the breeding season.
Prediction: Males will
spend more time searching
for missing females
Polygyny
Lek polygyny: Groups of males gather at a common display site (lek) that
females visit to select a mate.
Occurs when:
Why not just use scramble
competition polygyny?
1. Hotspot hypothesis
2. Hotshot hypothesis
3. Female preference
hypothesis
Example: Sage grouse lek
Polygyny
Lek polygyny: Groups of males gather at a common display site (lek) that
females visit to select a mate.
Hotspot hypothesis: Males cluster at leks because
Prediction: Leks should be
located in areas with higher
concentrations of nesting
females.
Polygyny
Lek polygyny: Groups of males gather at a common display site (lek) that
females visit to select a mate.
Hotshot hypothesis: Males cluster at leks because
Prediction: The most
successful location within a
lek will change from year to
year.
Polygyny
Lek polygyny: Groups of males gather at a common display site (lek) that
females visit to select a mate.
Female preference hypothesis: Males cluster at leks because
Prediction: Larger leks will attract
more receptive females.
Polyandry
Why might it be adaptive for a female to mate
with more than one male?
1. Polyandry provides females with
________ benefits.
A. Fertility insurance hypothesis
B. Good genes hypothesis
C. Genetic compatibility hypothesis
2. Polyandry provides females with
________ benefits.
A. More resources hypothesis
B. Better protection hypothesis
C. Infanticide reduction hypothesis
Not mutually exclusive.
Polyandry may be adaptive
in different species for
different reasons.
Polyandry
Polyandry provides females with genetic benefits.
Fertility assurance hypothesis: Mating with multiple males
Prediction: Gunnison’s prairie dog females
who are more polyandrous will be more likely
to become pregnant.
Polyandry
Polyandry provides females with genetic benefits.
Good genes hypothesis: Mating with multiple males
Prediction: Yellow-toothed cavy females
who mate with more than one male will
have more surviving offspring.
Prediction: Sons of sexually
successful field crickets will be more
attractive to females.
Polyandry
Polyandry provides females with genetic benefits.
Genetic compatibility hypothesis: Mating with multiple males
It is usually better for offspring to be heterozygous.
Prediction: In sand lizards, there should be a
negative relationship between the genetic
similarity of the male and female
(bandsharing) and the amount of offspring a
male sires.
Polyandry
Polyandry provides females with material benefits.
More resources hypothesis: Mating with multiple males
Prediction: Female leaf beetles who mate multiply will lay the same number of
eggs whether they mate with the same male or with different males.
Polyandry
Polyandry provides females with material benefits.
Better protection hypothesis: Mating with multiple males
Male damselflies will protect
females from harassment
by other males after they
have mated.
Prediction: Female damselflies will mate with more males when they
experience more harassment (at higher male densities).
Polyandry
Polyandry provides females with material benefits.
Infanticide reduction hypothesis: Mating with multiple males
Example: Female langurs will
copulate with multiple males, even
when they are not ovulating.
Infanticidal males that have
copulated with a female generally
leave her offspring alone.
Monogamy
Why might it be adaptive for a male to mate
with only one female?
1. Mate assistance hypothesis
2. Mate guarding hypothesis
3. Female-enforced monogamy
(monogamy is not adaptive for
males)
Not mutually exclusive.
Monogamy may be
adaptive in different species
for different reasons.
Monogamy
Mate assistance hypothesis: Monogamy is adaptive because
Prediction: Male care greatly
increases offspring survival
in the California mouse.
Monogamy
Mate guarding hypothesis: Monogamy is adaptive because
Prediction: In bank swallows, males will be most
attentive to their mates when they are fertile.
Monogamy
Female enforced monogamy hypothesis: Monogamy is not
adaptive for males
Prediction: Male burying
beetles will spend more time
releasing mate-attracting
pheromones when their first
mates are prevented from
stopping them.
Monogamy
Example: Researchers exposed socially monogamous yellow-breasted chats
to models of males and females of their own species and, as a control, a
wren model. They measured the relative aggression of male and female
yellow-breasted chats toward each of these models.
Which of the three hypotheses for monogamy are the results consistent with?
Monogamy
Social monogamy does not necessarily imply ________________.
Extra pair copulations (EPCs) by both genders are very common.
(Only 14% of bird species tested have true monogamy.)
Benefits to males of EPCs:
Benefits to females of EPCs: