Today: Monogamy xkcd.com

Reproduction reduces survival CB 53.8

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 Dogs Sexually monogamous female prairie dogs have a 92% chance of successfully giving birth.

Gunnison’s 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

Mating pairs may be genetically incompatible Cystic Fibrosis: F= normal, f= cystic fibrosis Mom=Ff Dad=Ff fF F f FFFf ffFf Mom=Ff Dad=FF fF F F FFFf FF Versus

Can females detect compatible genes?

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

Voles Prairie 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

Voles Prairie Monogamous Both parents care for young Montane Nonmonogamous Mother cares for young briefly

Voles Prairie 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.

Voles Prairie Monogamous Both parents care for young More receptors Montane Nonmonogamous Mother cares for young briefly Less receptors Same levels of oxytocin

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

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

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

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

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

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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