evolution and life histories ii. lh example: thrip egg mites ls: 4 days
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Evolution and Life Histories II
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• LH example: Thrip egg mites
LS: 4 days
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Life History Principles
• Generally begin with birds
• Reproductive output is accessible.
• Reproductive output can be easily manipulated and adjusted.
• Individuals can be marked for identification.
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The evolution of clutch size
• Optimal clutch size
• ? How much energy should an individual allocate to an episode of reproduction; e.g., how many eggs?
• Trade-off: The more offspring produced, the fewer resources available for each individual.
• Lack’s prediction: Selection should favor a clutch size that maximizes the number of surviving offspring.
• Clutch size should be a reproductive strategy.
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Tradeoff:Probability of individual survival< with > clutch size
Prediction: Number of survivingoffspring = clutch sizex probability of individual survival
Optimal clutchsize = 5
Assumptions: 1. eggs are all thesame size2. current reproductive effort does notaffect subsequentperformance
Starting hypotheses
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A test of the prediction: 1960-1982
Number ofClutchesN = 4489
Numbersurvivingas a functionof clutch size
Parental lifetime fitness can decrease from care necessitated by large broods.
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Future effects of clutch size on daughters’ performance
Collared Flycatchers
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Effect of age at first reproduction on size of subsequent clutches
• e.g. Collared Flycatchers
Begin atdifferent ages
Begin with extra eggs
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How large should offspring be?
• Trade-off between number and size of offspring.
• Produce many small OR few large?
• Can be dictated by environmental context; i.e., the reproductive strategy may include phenotypic plasticity
• e.g. Stator limbatus (a seed beetle)
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Seed beetle: Stator limbatus
Blue palo verde seedPoor host: < 1/2 larvae survive
Cat-claw acacia seedGood host: most larvae survive
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Optimal offspringsize for parent islarger on poor host
Minimum size atwhich offspringsurvive is smalleron good host
The model: Size decreases with anincreased number ofsibs
Offspringsurvival
Parentalfitness
Prediction: largereggs on poorer host
Stator limbatus
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1st egg onon host -then switched
Restricted to one host
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• A phylogenetic constraint on clutch size.
• A fitness enigma?
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A. tesselata (24.2 mL)
A. neotesselata (17.0 mL)
A. sexlineata (7.1 mL)
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Karyotype of Aspidoscelis neotesselata
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• Intraspecific divergence in life histories in A. tesselata (a parthenogenetic species)
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Fort Sumner
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Aspidoscelis tesselataPattern class E Pattern class C
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53 59 65 71 77 83 89 95 101
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Num
be
r
GravidNongravid
53 59 65 71 77 83 89 95 101SVL (mm)
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Num
be
r
GravidNongravid
Sumner C
Sumner E
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• Assignment: Sunday March 21• Watch “Life”: Cable TV, Discovery Channel • Making the series, 6 P.M.• Reptiles and Amphibians, 7 P.M.