Reports due Exam 3 take- home available soon Due Th 4/28

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

Sexual Dimorphism

Human Females: ~1 egg/month Human Males: 250,000,000 sperm/ ejaculation Fig 46.12

I hope Pat likes my feathers because I am tired of dragging them around everywhere. Fig 23.15

1 2 Which is male?

1 2

Sexual Dimporphism: morphological differences between males and females

Sexual Dimorphism

Male barn swallows have longer tails than females

Why do males have long tails? From “Biological Science” 3 rd ed. by Scott Freeman -fig 51.5

Why do males have long tails? From “Biological Science” 3 rd ed. by Scott Freeman -fig 51.5 feathers cut and reattached captured and released

Female grizzly bears cannot reproduce while lactating. Therefore they can only reproduce every once every 3 years…

…this leads to competition between males

Male elephant seals compete for access to females in limited beach territories. They are on average 4 times bigger than females. Male elephant seals weigh ~3 tons. From “Biological Science” 3 rd ed. by Scott Freeman -fig 25.14

Competition between males is fierce, only a few males father most of the offspring. 90% of males never successfully reproduce 60% of females do not successfully reproduce From “Biological Science” 3 rd ed. by Scott Freeman -fig 25.14

Average height/weight by sex in U.S.

Ratio of Weight Male/Female M/F

Primates have different reproductive stratagies

Testes Compared to Overall Weight Testicle size (oz) per body weight (lbs)

Our closest living relative... bonobos

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