Sexual Selection I
description
Transcript of Sexual Selection I
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Sexual Selection I
A broad overview
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Charles Darwin with his son William Erasmus in 1842
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Emma Darwin in 1840
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A section of Darwin’s “notes on marriage”, 1838.
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Lecture Outline
• Darwin and his addition to Natural Selection– Difficulties with Natural Selection– Definition and idea– Humans
• Modern Study of Sexual Selection– Types of study – Focus on advantages to mate choice
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Lecture Outline
• Darwin and his addition to Natural Selection– Difficulties with Natural Selection– Definition and idea– Humans
• Modern Study of Sexual Selection– Types of study– Focus on advantages to mate choice
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Examples of problematic phenomena for the theory of Natural Selection
• Peacocks’ tails
• Blackbird song
• Antlers in deer
• Sexual dimorphism in many species
• Mating display of Great Crested Grebe
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Examples of problematic phenomena for the theory of Natural Selection
• Peacocks’ tails (technically trains)
• Blackbird song
• Antlers in deer
• Sexual dimorphism in many species
• Mating display of Great Crested Grebe
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Lecture Outline
• Darwin and his addition to Natural Selection– Difficulties with Natural Selection– Definition and idea– Humans
• Modern Study of Sexual Selection– Types of study– Focus on advantages to mate choice
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Lecture Outline
• Darwin and his addition to Natural Selection– Difficulties with Natural Selection– Definition and idea– Humans
• Modern Study of Sexual Selection– Types of study– Focus on advantages to mate choice
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Darwin (1871, p256):
“We are, however, here concerned only with that kind of selection, which I have called sexual selection. This depends on the advantage which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction.”
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‘In relation to reproduction...’
• Being more noticed by, more attractive to, or more persuasive towards the opposite sex, and so gaining a mating advantage– Inter-sexual selection, ‘female’ choice
• Out-competing other members of the same sex in contests whose outcome determines mating success– Intra-sexual selection, ‘male’ competition
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Darwin’s criteria
• Age: juvenile vs adult
• Sex: male vs female
• Season: breeding season vs year-round
• Use: specially displayed during mating?
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Why does advantage in reproduction lead to exaggeration?
• ‘Disproportionate gains’– chooser makes an all or nothing choice
however small the difference is– all choosers may make the same choice
• Our similarity to targets of propaganda– any preference rule can be exploited– sensory systems have limitations
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Natural Selection vs Sexual Selection
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Natural Selection vs Sexual Selection
• Utilitarian, functional • Showy, elaborate
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Natural Selection vs Sexual Selection
• Utilitarian, functional• Solves a problem
• Showy, elaborate• Impresses an audience
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Natural Selection vs Sexual Selection
• Utilitarian, functional• Solves a problem• Sensible
• Showy, elaborate• Impresses an audience• Whimsical
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Natural Selection vs Sexual Selection
• Utilitarian, functional• Solves a problem• Sensible• Economical
• Showy, elaborate• Impresses an audience• Whimsical• Wasteful
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Natural Selection vs Sexual Selection
• Utilitarian, functional• Solves a problem• Sensible• Economical• Fixed
• Showy, elaborate• Impresses an audience• Whimsical• Wasteful• Changeable
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Natural Selection vs Sexual Selection
• Utilitarian, functional• Solves a problem• Sensible• Economical• Fixed• Constructive
• Showy, elaborate• Impresses an audience• Whimsical• Wasteful• Changeable• Destructive
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Natural Selection vs Sexual Selection
• Utilitarian, functional• Solves a problem• Sensible• Economical• Fixed• Constructive• Dull
• Showy, elaborate• Impresses an audience• Whimsical• Wasteful• Changeable• Destructive• Exciting
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Darwin (1871, p256):
“We are, however, here concerned only with that kind of selection, which I have called sexual selection. This depends on the advantage which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction.”
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Human traits possibly related to sexual selection
• Racial differences– skin colour– hair colour and texture
• Gender differences– physical– psychological
• Analogy to fashion in clothes and personal styles
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Lecture Outline
• Darwin and his addition to Natural Selection– Difficulties with Natural Selection– Definition and idea– Humans
• Modern Study of Sexual Selection– Types of study – Focus on advantages to mate choice
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Lecture Outline
• Darwin and his addition to Natural Selection– Difficulties with Natural Selection– Definition and idea– Humans
• Modern Study of Sexual Selection– Types of study– Focus on advantages to mate choice
![Page 34: Sexual Selection I](https://reader035.fdocuments.us/reader035/viewer/2022062309/56813c84550346895da62605/html5/thumbnails/34.jpg)
Lecture Outline
• Darwin and his addition to Natural Selection– Difficulties with Natural Selection– Definition and idea– Humans
• Modern Study of Sexual Selection– Types of study– Focus on advantages to mate choice
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Kinds of modern work (with one example)
• Field empirical– Møller on barn swallows
• Experimental– Gerhardt on tree frogs
• Comparative method– Eberhard on reproductive anatomy
• Concepts / Mathematical modelling– Lande on runaway processes
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Modern topics
• Fireflies
• Bird coloration
• Anatomy of reproductive organs
• Sperm competition
• Pollen competition
• Disease resistance
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Modern topics
• Fireflies
• Bird coloration
• Anatomy of reproductive organs
• Sperm competition
• Pollen competition
• Disease resistance
• … and more, discussed by Marian Dawkins later in the course
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Modern topics
• Fireflies
• Bird coloration
• Anatomy of reproductive organs
• Sperm competition
• Pollen competition
• Disease resistance
• … and more, discussed by Marian Dawkins later in the course
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Eberhard (1985)
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Population level effects...
• include polygamy, polyandry, leks and ruts
• are discussed further later in the course
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Lecture Outline
• Darwin and his addition to Natural Selection– Difficulties with Natural Selection– Definition and idea– Humans
• Modern Study of Sexual Selection– Types of study– Focus on advantages to mate choice
![Page 42: Sexual Selection I](https://reader035.fdocuments.us/reader035/viewer/2022062309/56813c84550346895da62605/html5/thumbnails/42.jpg)
Lecture Outline
• Darwin and his addition to Natural Selection– Difficulties with Natural Selection– Definition and idea– Humans
• Modern Study of Sexual Selection– Types of study– Focus on advantages to mate choice
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Modern study of sexual selection
• focusses mainly on preferences,
• treats preferences as adaptive,
• looks for a selective advantage to preference,
• and there are several possibilities.
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Females might choose
• non-adaptively: because of sensory bias, species recognition.
• adaptively directly: for reasons of fertilisation ability, fecundity, nutrition, parental ability, territory quality, avoiding venereal disease, social status of offspring
• adaptively through good genes: because of inherited attractiveness of sons, or heritable disease resistance, or more generally heritable ‘quality’.
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Some formal ideas
• Fisher’s runaway model
• Lande’s model
• Measuring Sexual Selection: Lande/Wade/Arnold
• Hamilton/Zuk
• Handicaps & Signalling
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Andersson (1994)
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Literature
• C. Darwin (1871) The Descent of Man and Selection in Relation to Sex. Republished in 1981 by Princeton University Press.
• Extracts in M.Ridley (1987) The Essential Darwin. Unwin Hyman.
• M. Andersson (1994) Sexual Selection. Princeton University Press.
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Lecture Outline
• Darwin and his addition to Natural Selection– Difficulties with Natural Selection– Definition and idea– Humans
• Modern Study of Sexual Selection– Types of study– Focus on advantages to mate choice
![Page 49: Sexual Selection I](https://reader035.fdocuments.us/reader035/viewer/2022062309/56813c84550346895da62605/html5/thumbnails/49.jpg)
Lecture Outline
• Darwin and his addition to Natural Selection– Difficulties with Natural Selection– Definition and idea– Humans
• Modern Study of Sexual Selection– Types of study– Focus on advantages to mate choice
![Page 50: Sexual Selection I](https://reader035.fdocuments.us/reader035/viewer/2022062309/56813c84550346895da62605/html5/thumbnails/50.jpg)
In summary,
• Darwin invented sexual selection to accommodate certain kinds of facts within his scheme, partly as a defence against non-biological theories
• He established there was female choice but said little about why
• We now assume selection is at work, and want to know why there is choice