Today: Monogamy

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Today Monogamy
xkcd.com
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(No Transcript)
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What different reproductive strategies exist, and
what are the benefits and risks?
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These birds are nesting together, they must be an
item
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10-40 of offspring in monogamous bird species
are fathered by an extra-pair male
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• Social Monogamy pair lives/works together, but
  not faithful
• Sexual Monogamy pair raise young and only
  copulate with each other

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Mating pairs share genetic information and
possibly help in child-rearing
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In mammals, child-rearing is most commonly done
by the female. She provides milk.
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Less than 0.01 of mammals are monogamous
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Do Males and Females have different attitudes
toward sex and relationships?
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On a college campus an attractive male or female
asked the opposite sex I have been noticing
you around campus. I find you very attractive

• Female answers
• Would you go out with me tonight?
• 50 yes

• Male answers
• Would you go out with me tonight?
• 50 yes

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On a college campus an attractive male or female
asked the opposite sex I have been noticing
you around campus. I find you very attractive

• Female answers
• Would you go out with me tonight?
• 50 yes
• Would you come to my apartment tonight?
• 6 yes

• Male answers
• Would you go out with me tonight?
• 50 yes
• Would you come to my apartment tonight?
• 69 yes

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On a college campus an attractive male or female
asked the opposite sex I have been noticing
you around campus. I find you very attractive

• Female answers
• Would you go out with me tonight?
• 50 yes
• Would you come to my apartment tonight?
• 6 yes
• Would you go to bed with me tonight?
• 0 yes

• Male answers
• Would you go out with me tonight?
• 50 yes
• Would you come to my apartment tonight?
• 69 yes
• Would you go to bed with me tonight?
• 75 yes

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Why do Males and Females have different attitudes
toward sex and relationships?
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The male perspective on monogamy
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Eggs require large resource input. A clutch of
bird eggs can be 20 of birds weight. Sperm
are cheap.
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A female kiwi ready to lay an egg.
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Eggs require large resource input. A clutch of
bird eggs can be 20 of birds weight. Sperm
are cheap.
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Female mammals provide additional resources in
form of milk.
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Why might females choose to mate with multiple
males?
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Gunnisons Prairie Dogs
Sexually monogamous female prairie dogs have a
92 chance of successfully giving birth.
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Gunnisons Prairie Dogs
Sexually monogamous female prairie dogs have a
92 chance of successfully giving
birth. Non-monogamous females have a 100 chance
of giving birth
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Mating pairs may be genetically incompatible
Cystic Fibrosis F normal, f cystic fibrosis
MomFf
f
F
F
FF
Ff
Versus
DadFf
MomFf
f
ff
Ff
f
F
F
FF
Ff
DadFF
F
Ff
FF
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Can females detect compatible genes?
http//www.pbs.org/wgbh/evolution/library/01/6/l_0
16_08.html
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Benefits for females choosing mates for good
genes vs compatible genes
Genetic quality and sexual selection an
integrated framework for good genes and
compatible genes. Neff and Pitcher Molecular
Ecology (2005) 14 pg19â 38
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Benefits for females choosing mates for good
genes vs compatible genes
Genetic quality and sexual selection an
integrated framework for good genes and
compatible genes. Neff and Pitcher Molecular
Ecology (2005) 14 pg19â 38
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How can a female know which male has successful
genes?
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Females may choose traits, like large displays,
that are disadvantageous for male survival.
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CB 51.30
How can females determine good males?
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CB 51.30
Color Bright coloring can be correlated with
health
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CB 51.30
But a male with a mate is judged as being high
quality even if he is less colorful
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Choosing a mate and reproductive strategies are
based on methods to succesfully pass on genes
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Voles

• Prairie
• Monogamous
• Both parents care for young

• Montane
• Nonmonogamous
• Mother cares for young briefly

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Oxytocin (hormone)
Encourages bonding between individuals
Water/salt balance
Contraction of womb and milk production
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Hormones are molecules produced in one cell and
signal another.
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Oxytocin (hormone)
Encourages bonding between individuals
Water/salt balance
Contraction of womb and milk production
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Voles

• Prairie
• Monogamous
• Both parents care for young

• Montane
• Nonmonogamous
• Mother cares for young briefly

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Voles

• Prairie
• Monogamous
• Both parents care for young

• Montane
• Nonmonogamous
• Mother cares for young briefly

Same levels of oxytocin
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Hormones are molecules produced in one cell and
signal another.
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Voles

• Prairie
• Monogamous
• Both parents care for young
• More receptors

• Montane
• Nonmonogamous
• Mother cares for young briefly
• Less receptors

Same levels of oxytocin
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Voles

• Prairie
• Monogamous
• Both parents care for young
• More receptors
• ?

• Montane
• Nonmonogamous
• Mother cares for young briefly
• Less receptors
• ?

Same levels of oxytocin
Inject hormone into brain
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Voles

• Prairie
• Monogamous
• Both parents care for young
• More receptors
• Monogamous

• Montane
• Nonmonogamous
• Mother cares for young briefly
• Less receptors
• Nonmonogamous

Same levels of oxytocin
Inject hormone into brain
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Voles

• Prairie
• Monogamous
• Both parents care for young
• More oxytocin receptors
• ?

• Montane
• Nonmonogamous
• Mother cares for young briefly
• Less oxytocin receptors
• ?

Same levels of oxytocin
Block receptors
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Voles

• Prairie
• Monogamous
• Both parents care for young
• More oxytocin receptors
• Nonmonogamous

• Montane
• Nonmonogamous
• Mother cares for young briefly
• Less oxytocin receptors
• Nonmonogamous

Same levels of oxytocin
Block receptors
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Voles

• Prairie
• Monogamous
• Both parents care for young
• More oxytocin receptors
• Monogamous

• Montane
• Nonmonogamous
• Mother cares for young briefly
• Less oxytocin receptors
• Monogamous

Same levels of oxytocin
Increase levels of receptors (genetically) in
ventral pallidum
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Voles

• Prairie
• Monogamous
• Both parents care for young
• More receptors

• Montane
• Nonmonogamous
• Mother cares for young briefly
• Less receptors

Same levels of oxytocin
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xkcd.com