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Biology 3466B Study Guide - Mating System, Assortative Mating, Long Tail

Course Code
BIOL 3466B
Yolanda Morbey

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Sexual Selection Ch. 11 401-441
Sexual selection differential reproductive success due to
variation among individuals in mating success
Predict whether traits will be subject to sexual
Explain why the strengths of sexual selection differ
between the sexes
Contrast intrasexual and intersexual selection and
their effects on mating behaviors (competition and
mate choice)
Sexual Dimorphism and Sex
Sexual dimorphism a difference between males and females
of a species
Darwin realized that individuals vary not only in their
success at surviving and reproducing but also in their
success at persuading members of the opposite sex to
Failing to mate is the same as dying young (no genetic
Theory of Evolution by Sexual Selection
If there is heritable variation in a trait that affects the ability to
obtain mates, then variants conductive to success will become
more common over time
Asymmetries in Sexual Reproduction
For sexual selection to explain differences between
sexes it must act on the sexes differently
In many animals, eggs (pregnancies) are more
expensive than ejaculates
Parental investment - Energy and time expended in
constructing and caring for an offspring (measure of fitness)
Mothers typically make larger parental investment to
each offspring than fathers
o Eggs more expensive than sperm
Increases the reproductive success of the offspring
receiving it
Decreases the reproductive success that investing
parent may achieve in the future (additional offspring)
In most animal species neither parents care for young
Sexual Selection Males vs. Females
The strength of sexual selection differs in males than in
When mother makes a larger investment:
Females potential success is small
Realized success is limited by number of eggs
Males potential success is large
Realized success is limited by # of female mates
Limits of reproductive success:
In the sex with greater parental investment limit is
time and resources
In sex with lower parental investment limit is mating
Limits of Reproductive Success in Newts
Mating system
Males arrive at breeding ponds early and stay long
Females visit ponds to mate with males
Females lay 300 eggs over several weeks or months
No parental care
Sexual selection was more powerful force in the
evolution of males
Heritable traits in males that are associated with
failure to mate will disappear
Heritable traits in males linked to mating success will
become common
For males more than females in many species fitness is
determined by access to mates
Limits of Reproductive Success in Pipefish (Sexual
Roles Reversed)
Mating system
Female lays eggs in brood pouch of makes
Males provide all parental care until eggs hatch
Females invested less energy which resulted in more
females with eggs to lay than males with space to
accept them
More females than males fail to mate
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