Today: Monogamy

xkcd.com

Reproduction reduces survival

CB53.8

What different reproductive strategies exist, and what are the benefits and risks?

These birds are nesting together, they must be an “item”

10-40% of offspring in “monogamous” bird species are fathered by an extra-pair male

•Social Monogamy = pair lives/works together, but not “faithful”•Sexual Monogamy = pair raise young and only copulate with each other

Mating pairs share genetic information and possibly help in child-rearing

In mammals, child-rearing is most commonly done by the female. She provides milk.

Less than 0.01% of mammals are monogamous

Do Males and Females have different attitudes toward sex and relationships?

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…”Male answers:…Would you go out

with me tonight?= 50% yes

Female answers:…Would you go out

with me tonight?= 50% yes

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…”Male answers:…Would you go out

with me tonight?= 50% yes…Would you come to

my apartment tonight?

= 69% yes

Female answers:…Would you go out

with me tonight?= 50% yes…Would you come to

my apartment tonight?

= 6% yes

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…”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

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

Why do Males and Females have different attitudes toward sex and relationships?

The male perspective on monogamy

Eggs require large resource input.

A clutch of bird eggs can be ~20% of bird’s weight.

Sperm are cheap.

A female kiwi ready to lay an egg.

Eggs require large resource input.

A clutch of bird eggs can be ~20% of bird’s weight.

Sperm are cheap.

Female mammals provide additional resources in form of milk.

Why might females choose to mate with multiple males?

Gunnison’s Prairie DogsSexually monogamous female prairie dogs have a 92% chance of successfully giving birth.

Gunnison’s Prairie DogsSexually monogamous female prairie dogs have a 92% chance of successfully giving birth.

Non-monogamous females have a 100% chance of giving birth

Mating pairs may be genetically incompatibleCystic Fibrosis: F= normal, f= cystic fibrosis

Mom=Ff

Dad=Ff

fF

F

f

FF Ff

ffFfMom=Ff

Dad=FF

fF

F

F

FF Ff

FfFF

Versus

http://www.pbs.org/wgbh/evolution/library/01/6/l_016_08.html

Can females detect compatible genes?

Genetic quality and sexual selection: an integrated framework for good genes and compatible genes.Neff and Pitcher Molecular Ecology (2005) 14 pg19– 38

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 pg19– 38

Benefits for females choosing mates for good genes vs compatible genes

How can a female know which male has successful genes?

Females may choose traits, like large displays, that are disadvantageous for male survival.

How can females determine “good” males?CB 51.30

Color:Bright coloring can be correlated with health…

CB 51.30

But a male with a mate is judged as being high quality even if he is less colorful

CB 51.30

Choosing a mate and reproductive strategies are based on methods to succesfully pass on

genes

VolesPrairie

• Monogamous• Both parents care

for young

Montane• Nonmonogamous• Mother cares for

young briefly

Oxytocin(hormone)

Water/salt balance

Contraction of womb and milk production

Encourages bonding between individuals

Hormones are molecules produced in one cell and signal another.

Oxytocin(hormone)

Water/salt balance

Contraction of womb and milk production

Encourages bonding between individuals

VolesPrairie

• Monogamous• Both parents care

for young

Montane• Nonmonogamous• Mother cares for

young briefly

VolesPrairie

• Monogamous• Both parents care

for young

Montane• Nonmonogamous• Mother cares for

young briefly

Same levels of oxytocin

Hormones are molecules produced in one cell and signal another.

VolesPrairie

• Monogamous• Both parents care

for young

• More receptors

Montane• Nonmonogamous• Mother cares for

young briefly

• Less receptorsSame levels of oxytocin

VolesPrairie

• 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

VolesPrairie

• 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

VolesPrairie

• 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

VolesPrairie

• 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

VolesPrairie

• 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

VolesPrairie

• Monogamous• Both parents care

for young

• More receptors

Montane• Nonmonogamous• Mother cares for

young briefly

• Less receptorsSame levels of oxytocin

xkcd.com