Lecture 25-SexSelection

Lecture 25-SexSelection - SexualDimorphism

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Sexual Dimorphism Males and females vary in characteristics Height Weight Ornamentation Coloration 1
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Sexual Dimorphism www.hlasek.com http://www.oiseaux.net/oiseaux/passeriformes/images/euplecte.a.longue.queue.wifr.0p.jpg 3
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Sexual Dimorphism 4
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Sexual Dimorphism http://coris.noaa.gov/glossary/sexual_dimorphism_186.jpg http://www.nano-reef.com/fish/images/obliquedottyback1.jpg 5
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Sexual Dimorphism http://z.about.com/d/animals/1/0/q/H/shutterstock_1147674.jpg http://www.oceanlight.com/thumbs/15497.jpg 6
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Natural Selection Traits that help individuals survive are passed on Traits become more frequent in population 7
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Natural Selection So why the differences between the sexes? Shouldn’t traits beneficial to one benefit the other? 8
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Some dimorphic traits are costly! E.g. long feathers 9
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Bird of Paradise 10
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Bird of Paradise 11
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Some traits are costly! Long feathers = increased predation risk Bright colors = increased predation risk Elaborate structures = increased energy to maintain 12
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So why does one sex have the (expensive) trait and the other doesn’t? 13
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Sexual Selection Failure to mate = evolutionary dead end Traits that increase mating success are adaptive The sexes differ in mating success and traits that increase it 14
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Differences in Parental Investment Females usually invest more in offspring production and rearing Parental investment increases reproductive success of offspring 15
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Differences in Parental Investment Females usually invest more in offspring production and rearing Parental investment increases reproductive success of offspring Parental investment limits fitness of parent by reducing resources for next (additional) offspring 16
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Differences in Parental Investment: Females Eggs are expensive Parental care (mother) is expensive Female potential reproductive success is limited by egg/offspring production Not limited by male mates available 17
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Differences in Parental Investment: Males Sperm is cheap Male potential mating success is unlimited Access to mates limits male mating success 18
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Sexual Selection Usually males are dramatically affected Females not 19
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Sexual Selection When evolution has selected for traits that increase reproductive success as a result of differences in mating success Attractiveness to mates Alternative mating strategies that maximize access to mates Traits that let some males have greater access to females 20
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This note was uploaded on 08/30/2008 for the course BIOS 230 taught by Professor Gibbons during the Spring '08 term at Ill. Chicago.

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Lecture 25-SexSelection - SexualDimorphism

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