BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.
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Transcript of BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.
![Page 1: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/1.jpg)
BIOE 109Summer 2009
Lecture 9- Part ISexual selection
![Page 2: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/2.jpg)
Sexual dimorphism is very common in nature
![Page 3: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/3.jpg)
What is sexual selection?
![Page 4: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/4.jpg)
What is sexual selection?
Natural Selection: Differential reproductive success due to variation among individuals in survival and reproduction.
![Page 5: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/5.jpg)
What is sexual selection?
Darwin (1871) defined sexual selection as: Differential reproductive success due to variation among individuals in success at getting mates.
![Page 6: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/6.jpg)
What is sexual selection?
Darwin (1871) defined sexual selection as: Differential reproductive success due to variation among individuals in success at getting mates. • sexual selection refers to one component of fitness: mating success.
Fitness = Viability +Fecundity +Longevity +Mating success
![Page 7: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/7.jpg)
What is sexual selection?
Fitness = Viability +Fecundity +Longevity +Mating success
![Page 8: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/8.jpg)
What is sexual selection?
Fitness = Viability +Fecundity +Longevity +Mating success
• “trade-offs” between fitness components may occur!
![Page 9: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/9.jpg)
What is sexual selection?
Fitness = Viability +Fecundity +Longevity +Mating success
• “trade-offs” between fitness components may occur!
• a trait improving mating success may increase total fitness yet reduce viability!
![Page 10: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/10.jpg)
If sexual selection is indeed the explanation for sexual dimorphism, then it will have to act on sexes differently…..
And it does!Sexual reproduction creates different selection pressures for males and females.
How?
![Page 11: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/11.jpg)
If sexual selection is indeed the explanation for sexual dimorphism, then it will have to act on sexes differently….. And it does! Sexual reproduction creates different selection pressures for males and females.
• Through asymmetric parental investment!
![Page 12: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/12.jpg)
What is parental investment?
Energy and time expended in either or both: -constructing an offspring -caring for it.
![Page 13: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/13.jpg)
What is parental investment?
Energy and time expended in either or both: -constructing an offspring -caring for it.
• Producing eggs (or pregnancies) are more expensive than ejaculates.
![Page 14: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/14.jpg)
What is parental investment?
Energy and time expended in either or both: -constructing an offspring -caring for it.
• Producing eggs (or pregnancies) are more expensive than ejaculates.
• In more than 90% of mammal species, females provide substantial parental care and males provide little to none.
![Page 15: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/15.jpg)
What acts to limit the lifetime reproductive success of males and females?
females: limited by no. of eggs and/or pregnancies
![Page 16: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/16.jpg)
What acts to limit the lifetime reproductive success of males and females?
females: limited by no. of eggs and/or pregnancies
males: limited by no. of females mated
![Page 17: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/17.jpg)
What acts to limit the lifetime reproductive success of males and females?
females: limited by no. of eggs and/or pregnancies
males: limited by no. of females mated (access to mates)
This sets up a conflict = sexual selection.
To understand sexual selection we must quantify the relationship between number of mates and reproductive success for both males and females
![Page 18: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/18.jpg)
Sexual selection in rough-skinned newts
![Page 19: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/19.jpg)
Sexual selection in rough-skinned newts
![Page 20: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/20.jpg)
Sexual selection in rough-skinned newts
Access to females increases reproductive success in males
![Page 21: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/21.jpg)
What does this mean?
• Heritable traits associated with mating success will become common in males
![Page 22: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/22.jpg)
What does this mean?
• Heritable traits associated with mating success will become common in males
tall creststhat appearduring breedingseason
![Page 23: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/23.jpg)
What does this mean?
• Heritable traits associated with mating success will become common in males
• Heritable traits that are not associated with mating success will tend to disappear from the population
![Page 24: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/24.jpg)
Sexual selection in pipefish
![Page 25: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/25.jpg)
A baby pipefish emerging from Dad’s brood pouch
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Sexual selection in pipefish
![Page 27: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/27.jpg)
Predictions:
Based on Parental Investment:
females: limited by no. of eggs and/or pregnancies
males: limited by no. of mates
Members of the sex subject to strong sexual selection will be competitive.
Members of the sex subject to weaker sexual selection will be choosy.
![Page 28: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/28.jpg)
Predictions:
1. Males should be competitive
![Page 29: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/29.jpg)
Predictions:
1. Males should be competitive
• they should compete among themselves for access to females.
![Page 30: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/30.jpg)
Predictions:
1. Males should be competitive
• they should compete among themselves for access to females.
• this is “male-male competition” or intrasexual selection.
![Page 31: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/31.jpg)
Predictions:
1. Males should be competitive
• they should compete among themselves for access to females.
• this is “male-male competition” or intrasexual selection.
2. Females should be choosy
![Page 32: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/32.jpg)
Predictions:
1. Males should be competitive
• they should compete among themselves for access to females.
• this is “male-male competition” or intrasexual selection.
2. Females should be choosy
• since her investment is larger, she has more to lose by making a bad decision.
![Page 33: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/33.jpg)
Predictions:
1. Males should be competitive
• they should compete among themselves for access to females.
• this is “male-male competition” or intrasexual selection.
2. Females should be choosy
• since her investment is larger, she has more to lose by making a bad decision.
• this is “female choice” or intersexual selection.
![Page 34: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/34.jpg)
Intrasexual selection
(male-male competition)
![Page 35: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/35.jpg)
Intrasexual selection
• occurs when individual males can monopolize access to females.
-Fight for control of mates and/or control of resources vital to mates
![Page 36: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/36.jpg)
Intrasexual selection
• occurs when individual males can monopolize access to females.
-Fight for control of mates and/or control of resources vital to mates
Types of intra-sexual selection:1. Combat2. Sperm competition3. Infanticide4. Sneaky strategy
![Page 37: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/37.jpg)
Intrasexual selection
• occurs when individual males can monopolize access to females.
1. Combat
• leads to sexual dimorphism in size
http://video.google.com/videoplay?docid=7730341199662689386&ei=OR2DSoK9KY-SqAOPmbijBA&q=male-male+competition+in+animals&hl=en&client=firefox-a
![Page 38: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/38.jpg)
Intrasexual selection
• occurs when individual males can monopolize access to females.
1. Combat
• leads to sexual dimorphism in sizeExample: northern elephant seal.
♂ ~ 4,000 lbs
♀ ~1500 lbs
![Page 39: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/39.jpg)
Intrasexual selection
1. Combat
• leads to sexual dimorphism in sizeExample: northern elephant seal.
• can also lead to the evolution of weaponry
![Page 40: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/40.jpg)
Intrasexual selection
1. Combat
• leads to sexual dimorphism in sizeExample: northern elephant seal.
• can also lead to the evolution of weaponryExample: horns in ungulates and beetles.
![Page 41: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/41.jpg)
Intrasexual selection
2. Sperm competition
![Page 42: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/42.jpg)
Intrasexual selection
2. Sperm competition
• If a female mates with two or more males, the male whose sperm win the race to the eggs has higher reproductive success.
![Page 43: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/43.jpg)
Intrasexual selection
2. Sperm competition
• If a female mates with two or more males, the male whose sperm win the race to the eggs has higher reproductive success.
• Ex. of traits needed to be successful• Large ejaculates• More and longer mating occurrences
![Page 44: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/44.jpg)
Intrasexual selection
2. Sperm competition
• If a female mates with two or more males, the male whose sperm win the race to the eggs has higher reproductive success.
• Ex. of traits needed to be successful• Large ejaculates• More and longer mating occurrences
• Other examples include Sperm plugs, scooping out sperm, prolonged copulation, guarding of mate, applying hormones that reduce female’s attractiveness to other males.
![Page 45: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/45.jpg)
Sperm competition in damselflies
barbed horns on penis
![Page 46: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/46.jpg)
Intrasexual selection
3. Infanticide
Example: the African lion
![Page 47: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/47.jpg)
Intrasexual selection
4. Alternative male reproductive strategies.
Example: Sneaky strategy in Pacific salmon.
Hooknoses (male- 18mon) Female
Jacks (male-6mon)
![Page 49: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/49.jpg)
Intersexual selection
• occurs when males “advertise” for mates and females choose among different males.• Elaborate courtship displays: singing,
dancing, or showing off bright color• leads to sexual dimorphism in ornate
features
![Page 50: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/50.jpg)
Intersexual selection:dancing…...
http://www.youtube.com/watch?v=bEhAbwCYc1c&NR=1
![Page 51: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/51.jpg)
Intersexual selectionsinging……
• http://www.youtube.com/watch?v=VjE0Kdfos4Y&NR=1&feature=fvwp
![Page 52: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/52.jpg)
Intersexual selection
• occurs when males “advertise” for mates and females choose among different males.• Elaborate courtship displays: singing,
dancing, or showing off bright color• leads to sexual dimorphism in ornate
featuresTypes of intersexual selection:
1. Direct Benefits-Acquisition of resources-Good genes
2. Pre-sensory Bias3. Runaway selection
![Page 53: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/53.jpg)
Intersexual selection
1. Direct benefits- Acquisition of resources
• females directly benefit from choosing certain males. Example: the common tern
![Page 54: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/54.jpg)
Intersexual selection
1. Direct benefits- Acquisition of resources
• females directly benefit from choosing certain males. Example: the common tern
• females show a strong preference for males that bring a lot of food.
![Page 55: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/55.jpg)
Intersexual selection
1. Direct benefits- Acquisition of resources
• females directly benefit from choosing certain males. Example: the common tern
• females show a strong preference for males that bring a lot of food. • the amount of food a male brings during courtship is strongly correlated with the amount he brings to feed young.
![Page 56: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/56.jpg)
1. Direct Benefits- Good genes
![Page 57: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/57.jpg)
1. Direct Benefits- Good genes
Example: call length of male gray tree frog
http://www.youtube.com/watch?v=0QhHB6_8SQU
![Page 58: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/58.jpg)
1. Direct Benefits- Good genes
Gerhardt et al. 1996
![Page 59: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/59.jpg)
1. Direct Benefits- Good genes
• females choose males with certain traits because they are honest “indicators” of overall genetic quality.
![Page 60: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/60.jpg)
1. Direct Benefits- Good genes
• females choose males with certain traits because they are honest “indicators” of overall genetic quality.
-calling in frogs-calling in birds-plumage color
![Page 61: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/61.jpg)
2. Sensory bias
![Page 62: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/62.jpg)
2. Sensory bias
• predicts that female preference for certain male traits evolves prior to the appearance of the male trait.
![Page 63: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/63.jpg)
2. Sensory bias
• predicts that female preference for certain male traits evolves prior to the appearance of the male trait.
• females have a pre-existing sensory bias for the trait and males exploit this preference.
![Page 64: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/64.jpg)
2. Sensory bias
• predicts that female preference for certain male traits evolves prior to the appearance of the male trait.
• females have a pre-existing sensory bias for the trait and males exploit this preference.
Example: Water mite (Neumania papillator)
![Page 65: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/65.jpg)
Water mite (Neumania papillator)
![Page 66: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/66.jpg)
3. Runaway selection
![Page 67: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/67.jpg)
3. Runaway selection
• results from a genetic correlation between a male trait and female preference for that trait.
![Page 68: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/68.jpg)
3. Runaway selection
• results from a genetic correlation between a male trait and female preference for that trait.
Components needed:-Assortative mating-Heritable trait
![Page 69: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/69.jpg)
3. Runaway selection
• results from a genetic correlation between a male trait and female preference for that trait.
• the simplest model assumes two genetic loci in linkage disequilibrium:
![Page 70: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/70.jpg)
3. Runaway selection
• results from a genetic correlation between a male trait and female preference for that trait.
• the simplest model assumes two genetic loci in linkage disequilibrium:
1. a female preference gene (P locus) for the male trait.
![Page 71: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/71.jpg)
3. Runaway selection
• results from a genetic correlation between a male trait and female preference for that trait.
• the simplest model assumes two genetic loci in linkage disequilibrium:
1. a female preference gene (P locus) for the male trait.
2. a gene for the male trait (T locus).
![Page 72: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/72.jpg)
3. Runaway selection
• results from a genetic correlation between a male trait and female preference for that trait.
• the simplest model assumes two genetic loci in linkage disequilibrium:
1. a female preference gene (P locus) for the male trait.
2. a gene for the male trait (T locus).
P T
![Page 73: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/73.jpg)
Example: stalk-eyed flies
![Page 74: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/74.jpg)
P T
Example: stalk-eyed flies
Preference Eye-stalkfor long lengtheye-stalks
![Page 75: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/75.jpg)
P T
Example: stalk-eyed flies
Preference Eye-stalkfor long lengtheye-stalks
mutation increasing♂ eye-stalk length…
![Page 76: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/76.jpg)
P T
Example: stalk-eyed flies
Preference Eye-stalkfor long lengtheye-stalks
mutation increasing♂ eye-stalk length…
…will be quickly drivento fixation by ♀ choice
![Page 77: BIOE 109 Summer 2009 Lecture 9- Part I Sexual selection.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cac5503460f9496ee58/html5/thumbnails/77.jpg)
P T
Example: stalk-eyed flies
Preference Eye-stalkfor long lengtheye-stalks
mutation increasing♂ eye-stalk length…
…will be quickly drivento fixation by ♀ choice
… resulting in continued exaggeration of ♂ trait
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♀ preference forlong eye-stalks
Elongation of♂ eye-stalks
Runaway selection
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LIMITS to Runaway selection:
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Recap
• Sexual selection explains sexual dimorphism in nature
• Asymmetry in parental investment leads to differential selection pressures in males and females (sexual selection)
• Sex that invests less is more “competitive”, sex that invests more is “choosy”
• Sexual selection is more potent force of evolution in males than in females (with few exceptions like pipe-fishes)
• Intersexual selection (male-male competition): leads to combat, spermCompetition, infanticides, alternative male strategies
• Intrasexual selection (female choice): due to direct benefits like resources, good genes etc., female sensory bias, runaway selection
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Interesting videos
• http://www.youtube.com/watch?v=GPbWJPsBPdA&NR=1For nest decoration of a Australian Bowerbird