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Today: Sexual Dimorphism

Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

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The male perspective on reproduction

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Page 1: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Today: Sexual Dimorphism

Page 2: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Why does sexual reproduction exist?

Cons:• Need two individuals• Hard to find mate• Diseases/Competition

Pros:• Genetic diversityor• Replace damage DNA

Page 3: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

The male perspective on reproduction

Page 4: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Eggs require large resource input.

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

Sperm are cheap.

Page 5: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

A female kiwi ready to lay an egg. Fig 25.13

Page 6: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Human Females:~1 egg/month

Human Males:250,000,000 sperm/ ejaculation

Fig 48.3

Page 7: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

I hope Pat likes my feathers because I am tired of dragging them

around everywhere.

Page 8: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

1

2

Which is male?

Page 9: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

1

2

Which is male?

Page 10: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Sexual Dimporphism: differences between males and females

Page 11: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Sexual Dimorphism

Page 12: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Male barn swallows have longer tails than females Fig 51.4

Page 13: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Fig 51.5Why do males have long tails?

Page 14: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Female grizzly bears cannot reproduce while lactating. Therefore they can only

reproduce every once every 3 years…

Page 15: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

…this leads to competition between males

Page 16: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Male elephant seals compete for access to females in limited beach territories. They are on average 4 times bigger than females.

Fig 25.14Male elephant seals weigh ~3 tons.

Page 17: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Competition between males is fierce, only a few males father most

of the offspring.

Fig 24.14

90% of males never successfully reproduce

60% of females do not successfully reproduce

Page 18: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Average height/weight by sex in U.S.

Page 19: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Ratio of Weight Male/Female

M/F

Page 20: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Primates have different reproductive stratagies

Page 21: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Testes Compared to Overall WeightTe

stic

le si

ze (o

z) p

er b

ody

wei

ght (

lbs)

Page 22: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Bonobos

Page 23: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Pipefish: related to seahorses

Page 24: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Pregnant Male:Males care for developing eggs

Page 25: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

If differences in reproductive behavior and morphology are based on sex roles, what happens when the roles are reversed?

Males care for developing eggs

Page 26: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

The Measurement of Sexual Selection Using Bateman’s Principles: An Experimental Test in the Sex-Role-Reversed Pipefish Syngnathus typhle (2005)Integrative and Comparative Biology, 45:874–884Adam G. Jones, Gunilla Rosenqvist, Anders Berglund, and John C. Avise

Page 27: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Jones et al. Fig. 1

freq

uenc

y

number of mates

When there are more females than males, many females cannot mate.

Page 28: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

freq

uenc

y

number of matesJones et al. Fig. 1

When the sex ratio is even, most males and females mate.

Page 29: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

freq

uenc

y

number of matesJones et al. Fig. 1

When there are more males than females, most males can mate.

Page 30: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Jones et al. Fig. 1

The sex ratio affects who will successfully reproduce. Pipefish females are more affected by competition.

Page 31: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

num

ber o

f ind

ivid

uals

body length (mm)Jones et al. Fig. 4

Excess females: only medium size females can mate

Page 32: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

num

ber o

f ind

ivid

uals

body length (mm)Jones et al. Fig. 4

Excess males: many different size males can mate

Page 33: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Jones et al. Fig. 4

medium sized female pipefish are most successful at reproducing while size is less critical for male pipefish

Page 34: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Different reproductive strategies lead to differences in sexual dimorphism.

Page 35: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

haploid

diploid

X 23in humans X 23

in humans

X 23in humans

Inheritance = The interaction between genes inherited from Mom and Dad.

Next: Inheritance