Transcript Chapter 11 sexual selection (slides 1

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Birds in Costa Rica
Bats in Israel
Squirrels in Canada
Monkeys in Ethiopia
Pronghorn in Montana
www.animalbehavior.org
• Asexual and
sexual
organisms
• Sex and gender
• Sexual selection
– Selection
affecting access
to gametes
http://www.micrographia.com/specbiol/cnidari/hydrozo/hydr010
0/hydra-01.htm
http://flickr.com/photos/billwalker/2521121709/
• Costs of sex
– Cost of meiosis
– Breakup gene
combinations
– Mate acquisition
– STDs
• Benefits of sex
– Adapt to changing
environment
• Abiotic
• Biotic
http://porpax.bio.miami.edu/~cmallery/150/life/meiosis.pics.jpg
• Pathological in tetrapods
• Simultaneous
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Earthworms, gastropods, hamlet fish
Self fertilization is rare
Costs: Double the sex organs
Benefits: When optimal sex for relative
size of mates changes
• Sequential
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Teleosts
Usually a one way ticket
Female  male in reef fish
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When harem male dies
Only large males can defend a territory
Male  female in sea bass
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Female reproductive output increases with
size
http://www.fsbio-hannover.de/oftheweek/196/800pxMating_earthworms.jpg
http://throughthestatic.wordpress.com/category/idio
ts/
• The evolution of
Anisogamy
– Females and males
• Consequences of
anisogamy
– Unequal parental investment
– Unequal variance in fitness
• Ornamented males
• Choosy females
– Easy males
http://www.microscopy-uk.org.uk/thedark/eggbigx.jpg
• Intra-sexual selection
– Interference competition
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Armaments (displays)
Size
Badges of status
• Inter-sexual selection
– Scramble competition
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Locomotion and mate
seeking
– Mate choice
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Ornamentation (displays)
Alternative tactics (e.g,
coercion, female mimicry)
• Sperm competition
• Given interference
competition
– Directional selection for
male size, armaments
– Decrease in males’ mean
viability
– Evolutionary “arms race”
– Distribution of male size as
costs balance benefits
– Mean investment is
proportional to number of
defended females
(reproductive variance)
http://www.innatmorrobay.com/elephant_seals_color.jpg
• Male size vs.
male trait size
• Shrinking
females
• Alternative
strategies
• Small male
advantage
http://crawford.tardigrade.net/journal/album/lillivatia.jpg
From Legrand and Morse 2000 Biol. J. Lin. Soc. 71:643-664
• Amplexus
– Female
receptivity is
limited, cyclic,
asynchronous
– Males are
available to
reproduce almost
continuously
http://www.treknature.com/gallery/Middl
e_East/Turkey/photo164737.htm
• Mate guarding in
birds
From Birkhead 1979 Anim. Behav. 27:866-874
• The importance of the
question
• The operational sex
ratio (OSR)
• The potential
reproductive rate (PRR)
• The differential cost of
reproduction
– Covaries with OSR and
PRR
From Amundsen & Forsgren 2001 PNAS 98:13155-13160
• Definition
• Kinds
– Fertilization
success
– Protection
– Resources
• Territories
• Parental care
• Nuptial gifts
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Nutritious ejaculates
Sexual cannibalism
http://www.biology.au.dk/trine.bilde.htm
Photograph by Medford Taylor
Male cost
trait
linkage
Genetic
of
Benefit
Female
preference
Generations
Different genes
promoting trait /
preference
Trait size
• Lande’s version
– Quantitative genetic
– Runaway when B / G > (v2 / w2 ) + 1
– In other words, when CVA (B) is high relative to VA
of trait (G) with low variance in female preference
(v2), weak utilitarian selection on trait (high w2)
– Requires initial
preference!
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Natural selection
Drift
Sensory
exploitation
• P1: Additive genetic variance for trait and
preference
– Generally supported
– Traits are influenced by several loci
• P2: Genetic co-variation between trait and
preference
– Method 1: Select for trait, see if preference also
changes
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Generally supportive
– Method 2: Is there covariation among traits in
brothers and preferences in sisters?
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Supported in sticklebacks and crickets