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27/Jan/2014
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ANT DIVERSITY
LECTURE 03
Spring 2014: Mondays 10:15am – 12:05pm (Fox Hall, Room 204)
Instructor: D. Magdalena SorgerWebsite: theantlife.com/teaching/bio295-islands-evolution
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Today:
Follow‐up on minute papers
Sources of variation
Phenotypic plasticity
Guest speaker: Dr. Terry Campbell
Summary
FOLLOW-UP MINUTE PAPERS
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Follow‐up on minute papers
• Scientific writing process (how long? Work distributed among group? Authorship? Order of writing?)
• Marcupials vs. placentals
• Neutral theory of evolution
• Epigenetics – royal jelly in honey bees?
• “optimal fitness level” – no need to evolve further?
Evolution does not optimize. It only improves. Just needs to be good ENOUGH.
Environments change. What is good (enough) today might not be good (enough) tomorrow. predator/prey, host/parasite, climate change
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Red Queen = evolutionary arms race
Through the Looking Glass (Lewis Carroll 1871, illustration by John Tenniel )
must constantly adapt, evolve, and proliferate to survive
around ever‐evolving organisms in an ever‐changing environment
‘(…) it takes all the running you can do to keep in the same place.’
How to test for Red queen dynamics?
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…seems to involve time travel…
COMPARE success of past and future generations of predators
AGAINSTcurrent prey populations
CASE STUDY
DAPHNIA
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Water flea (Daphnia magna)
DAPHNIA
Life history
Daphnia:
planktonic crustaceans
Crustacea, Branchiopoda (class), Cladocera(order)
1‐5 mm in length
lifespan 5‐6 months in typical conditions
DAPHNIA
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Parasite: Pasteuria ramosa
DAPHNIA
Life history
P. ramosa:
spore‐forming bacterium
infects water fleas
makes them bloated
darkens their body
castrates them in the process
DAPHNIA
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Infected water flea
DAPHNIA
Life history
Host & parasite produce resting stages
Accumulate in lake sediment
DAPHNIA
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DAPHNIA
METHODS
Dormant eggs reactivated (over 39‐year period)
Daphnia exposed to parasites from different time periods:
‐ Contemporary
‐ Past
‐ Future
DAPHNIA
De Caestaecker et al. 2007
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METHODS
DAPHNIA
39 years
39 years ago TODAY20 years ago
De Caestaecker et al. 2007
METHODSDAPHNIA
39 years
39 years ago TODAY20 years ago
De Caestaecker et al. 2007
INFECTIVITY LOWERDaphnia evolved to beat past parasite genotypes
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METHODS
DAPHNIA
39 years
39 years ago TODAY20 years ago
De Caestaecker et al. 2007
INFECTIVITY LOWERParasite adaptations specific to current host populations
METHODSDAPHNIA
39 years
39 years ago TODAY20 years ago
De Caestaecker et al. 2007
CONTEMPORARY paras i tes
NO OVERALL CHANGE IN INFECTIVITY (no significant difference between infectivity rates)Relative success of host and parasite remains
the same over the generations
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How cool is that?
Researchers managed to reactivate 700‐year‐old Daphnia!!!
DAPHNIA
CASE STUDY
CUCKO
O
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Life history
Brood parasites
Lay eggs in nests of other species (hosts)
Get young raised for free
Brood parasite gains benefit, host suffers
Not all cuckoo species cheat (60 % are parental)
Cheating habit evolved 3 times independently
CUCKO
OLife history: how they cheat
Female cuckoo finds host nest
Watches hosts build
Waits until hosts have begun clutch
Parasitizes during nest hosts’ laying period Removes one host egg (swallows it)
Very quick Cuckoo chick hatches first Ejects other eggs and chicks
CUCKO
O
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Host defenses
REJECT IF:
• single egg in nest
• poorly matched egg
• egg laid too early (before hosts begin to lay)
• hosts see cuckoo on their nests
CUCKO
OEvolutionary arms race
Defenses evolve in response to parasitism
Species untainted by cuckoos show no rejection of odd eggs
Egg patterns evolve
Species exploited by cuckoos have less variation in appearance of eggs within a clutch and more variation between clutches of different females
CUCKO
O
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Not parasitizing
No rejection
Parasitizing
Egg rejection
Egg mimicry
More distinctive egg signatures
Better egg mimicry
Evolutionary arms race
CUCKO
O
HOST SPECIES
CUCKOO
EGG MIMICRYCUCKO
O
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CHICK MIMICRY
CUCKO
O
CUCKOO HOST
Πάντα ῥεῖ (panta rhei)
Everything flows.
Characterizing Heraclitus’ thought (by Simplicius, & Plato)
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VARIATION
ANT
FISH
MONKEY
BIRD
SHRIMP
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Artforms of Nature (Ernst Haeckel, 1904)
Thalamphora= ForaminiferaAmoeboid protists
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Artforms of Nature (Ernst Haeckel, 1904)
DiscomedusaeJellyfish
Artforms of Nature (Ernst Haeckel, 1904)
ArachnidaArachnids
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Artforms of Nature (Ernst Haeckel, 1904)
ChiropteraBats
SOURCES OF VARIATION
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GENOTYPE inherited instructions carried within genetic code
PHENOTYPEobservable characteristics or traits of an organism (morphology, development, biochemical or physiological properties, phenology, behavior)
GENOTYPE+ environment = PHENOTYPE
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EPIGENETICS
Heritable changes in gene activity that are NOT caused by changes in the DNA sequence
For instance:
• DNA methylation & histone modification …alters gene expression without altering DNA sequence
• Maternal effects
Maternal effects
Effects of mother on her offspring due to non‐genetic influences
Amount and composition of yolk in eggs
Amount and kind of maternal care provided
Mother’s physical condition while she carries eggs/embryo
Consumption of alcohol/tobacco/drugs by pregnant women increases risk of non‐genetic birth defects in babies
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How to determine whether characteristics are genetic, environmental or both?
How to determine whether characteristics are genetic, environmental or both?
Backcrossing (Test cross)
Correlation
Common garden experiments
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BACKCROSSING
Mendelian ratios serve as evidence of simple genetic control
BACKCROSSINGA A
A a
a a
Mendelian Genetics
homozygous dominant
heterozygous
homozygous recessive
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Mendelian Genetics
3:1
F1 generation
F2 generation
2:2 4:0
Parent generation
Parent ParentParent
BACKCROSSING
CORRELATION
between average phenotype of offspring and that of parents or resemblance among siblings (greater than among unrelated individuals)
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CORRELATION
CORRELATION
Williams RW (2000) Mapping genes that modulate brain development: a quantitative genetic approach. In: Mouse brain development (Goffinet AF, Rakic P, eds). Springer Verlag, New York, pp 21–49.
Figure 2. The correlation between brain weights of parents and their offspring estimates heritability. Animals are from a multigenerational cross between C57BL/6J and DBA/2J inbred strains (G. Zhou and R. W. Williams, in progress). Parental values are the average unfixed weights of mothers and fathers without correction for variation in age or body weight. Offspring data are average brain weight per litter. Brains weights are also presented without correction for variation in body weight, sex, or age. Offspring weights tend to be slightly less than those of the parents because of offspring are on average about 50 days younger. The correlation between pairs of values is 0.38 and is a direct estimate of the narrow‐sense heritability of brain weight in this cross and environment. Correlations between mothers and offspring and fathers and offspring do not differ significantly. Thus, this estimate of heritability is not inflated by maternal effect.
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COMMON GARDEN EXP.
Rear offspring from phenotypically different parents in uniform environment and see if phenotypic differences in offspring persist
At least 2 generations are advisable to distinguish from maternal effects
COMMON GARDEN
EXP.
RESEARCH QUESTIONAre observed morphological differences among wild populations of Anolis carolinensis a result of genetic changes among populations or phenotypic plasticity
during development and growth?
Yoel Stuart
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COMMON GARDEN
EXP.
METHODS• Catch individuals from wild
populations
• Collect eggs, incubate and hatch
Do offspring maintain differentiation observed in wild under common growth conditions?
If yes: Evidence that observed differences have an evolved, genetic component
Yoel Stuart
PHENOTYPIC PLASTICITY
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PHENOTYPIC PLASTICITY
ability of an individual to express different features under different environmental conditions
NORM OF REACTIONof a genotype is the set of phenotypes it expresses in different environments
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Snow geese Chen caerulescens: white and blue form
Cepea nemoralis variation
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Bivalve Donax variabilis variation
Peppered moth Biston betularia: 2 forms
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Biston petularia larvae: 2 morphs
Wet season form Dry season form
Peacock Pansy Junonia almana:
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Reversible vs. irreversible plasticity
Behavioral: Tadpoles change foraging patterns in response to presence of
predators
Physiological: Increase in mitochondrial density in terrestrial vertebrates in
response to experiencing lower oxygen levels Changes in specific fatty acids incorporated into animal cell
membrane in response to changing thermal conditions
Morphological: Gills of aquatic salamander increase/decrease in response to
oxygen levels they receive Muscles in vertebrates get bigger when used
Reversible plasticity
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appears when environmental conditions change, often within an individual’s lifetime
Reversible plasticity
Reversible plasticity
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Organism adjusts timing of life history event: Annual plant flowering in response to lighting conditions
Features that cannot be altered once expressed: Water fleas (Daphnia) develop spines and thicker carapace in response to presence of predatory fly larva in pond (can’t be altered even if predator disappears)
Species of African acacia develops long spines on its stems in response to being browsed by giraffes and elephants (spines remain even if browsing stops)
Irreversible plasticity
Irreversible plasticity
Typical and predator‐induced morphs of Daphnia cucullata
Agrawal et al. 1999
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appears when environmental conditions are less volatile and less likely to change drastically
within lifetime of individual
Irreversible plasticity
Being phenotypically plastic can be an adaptation.
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Adaptive plasticity should evolve when…
individuals with capacity to adjust their development to conditions outperform individuals who express same trait constitutively
Adap
tive plasticity
Shade avoidance in plants (Impatiens capensis)
Individual can perceive presence of other plants
(= competition)
2 phenotypes:
Elongated, shade‐adapted
Short, sun‐adapted
Dudley & Schmitt 1996
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Adap
tive plasticity
ARE PHENOTYPES ADAPTIVE?
Test by doing transplant experiment:
put both phenotypes in both environments, see which ones do better
Dudley & Schmitt 1996
Adap
tive plasticity
If the two environments are experienced frequently enough under natural conditions then more plastic genotypes do better on average than less plastic ones
Dudley & Schmitt 1996
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Isn’t being plastic ALWAYS better then?
…consider costs!
Costs of plasticity
Maintenance – energetic cost of sensory and regulatory mechanisms
Production – excess cost of producing structure plastically
Information acquisition – energy/time cost of sampling
environment, could be used otherwise
Developmental instability – reduced canalization, developmental
imprecision
Genetic costs – deleterious effects of plasticity genes through linkage
with other genes (pleiotropy, epistasis)
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CASE STUDY
HONEYBEES
Life historyHONEYBEES
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Ant life cycle
HONEYBEES
Bee life cycleHONEYBEES
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Bee life cycle
HONEYBEES
worker (female)
Fertilized egg Unfertilized egg
queen(female)
drone(male)
Dr. David TarpyAssociate Professor
Dr. Ming Hua Huangformer Postdoctoral Fellow (Tarpy Lab)
HONEYBEES
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Queen morphs
HONEYBEES
Life historyHONEYBEES
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HONEYBEES
Larval stage: on average 5 days
Day 0 Day 1 Day2 Day 3 Day 4 Day 5
METHODS
Transfer to queen chamber
worker larva
DAY(start feeding royal jelly)
RESULTSHONEYBEES
Reproductive quality
low
high
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HONEYBEES
Reproductive quality
low
high
critical age
DAY(start feeding royal jelly)
RESULTS
Royal jelly (royalactin) & fruit flies
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GUEST SPEAKER
Dr. Terry Campbell
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SUMMARY
SUMMARY
1. What was the most important thing you learned during this class?
2. What important question regarding what you learned remains unanswered for you? (What would you like to know about next?)
NAME & DATE 1/27/2014
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For next week:
The Beak of the Finch: Read Chapter 4
Read paper (will be posted)
Homework 1 due Tuesday, February 4th 5pm (submit electronically)
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