Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to...
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Transcript of Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to...
![Page 1: Today: Sexual Dimorphism. Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity.](https://reader035.fdocuments.in/reader035/viewer/2022062909/5a4d1bb47f8b9ab0599ce080/html5/thumbnails/1.jpg)
Today: Sexual Dimorphism
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Why does sexual reproduction exist?
Cons:• Need two individuals• Hard to find mate• Diseases/Competition
Pros:• Genetic diversityor• Replace damage DNA
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The male perspective on reproduction
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Eggs require large resource input.
A clutch of bird eggs can be ~20% of bird’s weight.
Sperm are cheap.
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A female kiwi ready to lay an egg. Fig 25.13
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Human Females:~1 egg/month
Human Males:250,000,000 sperm/ ejaculation
Fig 48.3
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I hope Pat likes my feathers because I am tired of dragging them
around everywhere.
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Which is male?
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Which is male?
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Sexual Dimporphism: differences between males and females
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Sexual Dimorphism
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Male barn swallows have longer tails than females Fig 51.4
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Fig 51.5Why do males have long tails?
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Female grizzly bears cannot reproduce while lactating. Therefore they can only
reproduce every once every 3 years…
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…this leads to competition between males
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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.
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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
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Average height/weight by sex in U.S.
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Ratio of Weight Male/Female
M/F
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Primates have different reproductive stratagies
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Testes Compared to Overall WeightTe
stic
le si
ze (o
z) p
er b
ody
wei
ght (
lbs)
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Bonobos
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Pipefish: related to seahorses
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Pregnant Male:Males care for developing eggs
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If differences in reproductive behavior and morphology are based on sex roles, what happens when the roles are reversed?
Males care for developing eggs
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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
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Jones et al. Fig. 1
freq
uenc
y
number of mates
When there are more females than males, many females cannot mate.
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freq
uenc
y
number of matesJones et al. Fig. 1
When the sex ratio is even, most males and females mate.
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freq
uenc
y
number of matesJones et al. Fig. 1
When there are more males than females, most males can mate.
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Jones et al. Fig. 1
The sex ratio affects who will successfully reproduce. Pipefish females are more affected by competition.
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num
ber o
f ind
ivid
uals
body length (mm)Jones et al. Fig. 4
Excess females: only medium size females can mate
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num
ber o
f ind
ivid
uals
body length (mm)Jones et al. Fig. 4
Excess males: many different size males can mate
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Jones et al. Fig. 4
medium sized female pipefish are most successful at reproducing while size is less critical for male pipefish
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Different reproductive strategies lead to differences in sexual dimorphism.
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haploid
diploid
X 23in humans X 23
in humans
X 23in humans
Inheritance = The interaction between genes inherited from Mom and Dad.
Next: Inheritance