Mating Systems Species-specific pattern of association between males, females and offspring April 14: Mating Systems: Definitions What defines a mating system • Whether each individual of a given sex mates with one or many of the opposite sex • Who cares for the offspring Name Male-female association Sex providing care Examples Monogamy 1 female : 1 male Both Many birds Polygyny >1 female : 1 male Females Many mammals; some birds Polyandry 1 female : >1 male Males (sometimes both) Some birds; many insects Polygynandry >1 female : >1 male Both (or only males) Some birds; some fish Promiscuity >1 female : >1 male Neither (or only females) Many fish; chimpanzees
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Mating Systems - Michigan State University · 2003. 4. 28. · Mating Systems Species-specific pattern of association between m ales, fem ales and offspring April 14: Mating Systems:
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Mating System
sSpecies-specific pattern of association betw
een males, fem
ales and offspring
April 14: M
ating Systems: D
efinitions
What defines a m
ating system•
Whether each individual of a given sex m
ates with one or
many of the opposite sex
•W
ho cares for the offspring
Nam
eM
ale-female association
Sex providing careE
xamples
Monogam
y1 fem
ale : 1 male
Both
Many birds
Polygyny>1 fem
ale : 1 male
Females
Many m
amm
als;som
e birds
Polyandry1 fem
ale : >1 male
Males (som
etimes both)
Some birds;
many insects
Polygynandry>1 fem
ale : >1 male
Both (or only m
ales)Som
e birds;som
e fish
Promiscuity
>1 female : >1 m
aleN
either (or only females)
Many fish; chim
panzees
Cares
Cares
Deserts
Male
Fem
aleO
utcome m
atrix
Why D
o Mating System
s Vary A
mong Species?
Mating system
results from conflict of interest betw
een males
and females (and is outcom
e of evolutionary game)
•For both sexes, R
S would be m
aximized by having m
ultiple mates,
and having each mate care for offspring produced
•W
hether either sex can achieve this outcome depends upon sex-
specific ecological factors
April 14: M
ating Systems: W
hy variation?Deserts
Monogam
y(&
polygynandry)
Promiscuity
Polyandry
Polygyny
•O
ffspring require high parentalinvestm
ent, and/or•
Fem
ales widely dispersed (hence
not defendable by males)
•O
ffspring can be reared byone parent
•F
emale not w
idely dispersed(hence defendable)
“Monogam
y” in Birds
April 14: M
ating Systems: B
ird monogam
y
More than 90%
of bird species are socially monogam
ous•
Males and fem
ales form stable pair for duration of breeding season
(sometim
es longer)•
Both parents help rear offspring
But…
...•
DN
A fingerprinting studies find high levels of
Extra-Pair C
opulation (EPC
)•
Both m
ales and females m
ust be fooling around•
Raises functional questions
“Monogam
y” in Birds
April 14: M
ating Systems: B
ird monogam
y
Why should m
ales and females seek E
PC
s?•
Males: R
S maxim
ized by finding additional mating
opportunities (but there may be costs)
•Fem
ales: RS not lim
ited by mating opps, so w
hyseek additional ones?•
Benefits of genetic diversity
•G
ood genes (better than mate’s)?
Why should E
PC
s be furtive?•
Males: fem
ale may leave altogether (find m
ale that will invest m
ore)•
Females: m
ale incentive to invest in brood is diluted by loss of paternity
Fig. 13.7 A
lcock:B
lue tit males that attract
more E
PCs have m
orefaithful m
ates
Female visits per hour
Ow
n mate’s
absencesper hour
In other species, tendency to attract extra-pair females is
correlated with the sam
e sort of traits (song, plumm
age) thataffect ability to attract first m
ate
Genetic diversity and m
ate choice in mam
mals
April 14: M
ating Systems: B
ird monogam
y
Fem
ales mam
mals benefit by having offspring that are heterozygous at
MH
C* locus (allow
s greater diversity of antibody production)
•W
ith respect to MH
C, the ideal m
ate is one different from you
•H
uman m
ated pairs more likely to differ at M
HC
than youw
ould expect for random m
ating (I.e., mating is assortative)
•W
omen prefer the body odor of m
en who are different at M
HC
to that of men or are sim
ilar at MH
C (Sw
eaty T-shirt test)
MH
C*: M
ajor Histocom
patibility Com
plex: a highly polymorphic
(many allele) gene com
plex involved in imm
une response
Suggests advantage of extra-pair copulations by female: don’t put all
your eggs in one MH
C basket
Polygyny IA
pril 14: Mating System
s: Polygyny
I. Polygyny based on resource defense
•M
ales that offer better resources (e.g. territory) may attract additional m
ates
Major functional question in resource defense polygyny: w
hy shouldfem
ale settle with already m
ated male?
•She m
ust share resources with fem
ale already there (CO
ST)
•She can’t count on as m
uch help from m
ale (CO
ST)
Male red-w
inged blackbirdfem
ale
Resource D
efense Polygyny (cont’d)A
pril 14: Mating System
s: Polygyny
H1: P
erhaps quality of territory more than com
pensates for costs•
Typically it doesn’t--secondary fem
ales would probably produce m
oreoffspring if they found unm
ated male
Major functional question in resource defense polygyny: w
hy shouldfem
ale settle with already m
ated male?
H2: P
erhaps there are good-genes benefits (Sexy Son hypothesis)•
This w
orks only if male m
ating success is highly heritable•
Male m
ating success IS heritable, but heritable enough for females to have
a chance of recouping costs by producing sexy sons