Misconceptions About Indirect Genetic Effects in Behavioral...
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Misconceptions About Misconceptions About Indirect Genetic Effects in Indirect Genetic Effects in
Behavioral EvolutionBehavioral Evolution
Stephen M. ShusterStephen M. ShusterNorthern Arizona University
Interacting Phenotypes: Applying Indirect Genetic Effects to Behavioral Ecology
B. H Bleakley and S. M. Shuster, Organizers46th Animal Behavior Society Meeting, Pirenópolis, Brazil
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OutlineOutline
1.Current applications of IGEs2.“Alexander’s Paradigm”
3.Some misconceptions4.Some possible solutions
5.Summary and conclusions
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IGEsIGEs in Behavioral Ecologyin Behavioral Ecology
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Most Behavioral Researchers Accept:Most Behavioral Researchers Accept:•Individual phenotypes are influencedare influenced by social
partners•If genetically basedgenetically based,
social selection on traits can be reciprocal
•If traits are genetically genetically correlatedcorrelated, evolutionary
dynamics can be complicated
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But Is There A Disconnect?But Is There A Disconnect?
•Animal behaviorists seem to understand the theoretical constraints underlying
evolutionary change. •Yet they often neglect to apply these concepts when identifying and testing hypotheses about behavioral evolution.
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AlexanderAlexander’’s Paradigms Paradigm
Richard D. Alexander
The Evolution of Social Behavior, 1974. Annual Review
of Ecology and Systematics, Vol. 5 (1974), pp. 325-383
“For several years the study of social behavior has been
undergoing a revolution with far-reaching consequences
for the social and biological sciences (1974, p. 325).
Partly responsible are threethreerecent changes in the
attitudes of evolutionary biologists.
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AlexanderAlexander’’s Paradigms Paradigm
“First was growing acceptance of the evidence that the potency of natural
selection is overwhelmingly overwhelmingly concentrated at levels no
higher than that of the individual.
George C. Williams
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AlexanderAlexander’’s Paradigms Paradigm“Second was revival of the
comparative methodcomparative method, especially as applied to
behavior and life histories.
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Harcourt et al. 1981
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AlexanderAlexander’’s Paradigms Paradigm“Third was spread of the realization that not only
are all aspects of structure and function of organisms to be understood solely solely as products of
selection, but because of their peculiarly direct peculiarly direct relationship to the forces of selection, behavior and life historybehavior and life history
phenomena, long neglected by the evolutionists, may be among the most predictablemost predictable of all
phenotypic attributes.”
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AlexanderAlexander’’s Paradigm Restated,s Paradigm Restated,
1.Natural selection occurs “overwhelmingly” at the
individual level.
2. Traits that evolve in one species are likely to evolve in
analogous ways in other species.
3. A “peculiarly direct”relationship exists between apparent selection and trait
evolution.
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http://images.shoutwire.com/pic_full/5504796879097d1a-73c9-441e-a701-18f2cc4f3c21.JPG
But is there more to understanding behavioral evolution than this?
AlexanderAlexander’’s Home Runs Home Run
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In Particular,In Particular,1.Does natural selection really occur
“overwhelmingly” at the individual level?
2. Are traits that evolve in one species likely to evolve in the same way in other species?
3. Does a “peculiarly direct” relationship exist between apparent selection and trait evolution?
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Contextual Selection in Contextual Selection in PiPiññonon JaysJays
Photo credit Harold Stiver
Benford 2008; Benford et al., in review
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SamplingSampling• Uniquely color banded
• 13 morphological measurements
• Genotypes at 8 microsatellite loci
• Gender
• Survivorship
• Flock membership
Photo credit Russ Balda
Photo credit Bryce Marshall
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2002-2003 “100-Year” Drought
Record high heat and low precipitation
Pine ecosystems severely stressed
Photo credit Tom Whitham
Data courtesy National Climactic Data Center 2008
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Two phenotypes
PC1: (n = 247, t = 2.45, p = 0.01)PC2: (n = 247, t = 1.75, p = 0.08)
Photo credit Pam Koch
• Physiological capacity (PC1)
• Social status (PC2)
Individual SurvivorshipIndividual Survivorship
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Relative Fitness Among FlocksRelative Fitness Among Flocks
Juvenile fitness increased in some flocks but not others
Adult fitness decreased in some flocks but not others
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Contextual Selection in Contextual Selection in PiPiññonon JaysJays
In piñon jays (Gymnorhinuscyanocephalus), individual fitness is influenced by bill
size, bib size, “social dominance.”
An important component of fitness ALSO arises from
group membershipgroup membership.
This does not mean that “altruism” is favored in piñon
jays.
Only that members of some groups do better than others.
Photo credit Harold Stiver
Photo credit Edward Rooks
Benford 2008; Benford et al., in review
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Contextual Selection in Contextual Selection in PiPiññonon JaysJays
Ignoring the component of selection that arises due to group
membership (i.e., social interaction)
only gives a partial partial viewview of how total
selection operates.
Photo credit Harold Stiver
Photo credit Edward Rooks
Benford 2008; Benford et al., in review
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In Particular,In Particular,1.Does natural selection occur
“overwhelmingly” at the individual level?
2. Are traits that evolve in one species likely to evolve in the same way in other species?
3. Does a “peculiarly direct” relationship exist between apparent selection and trait evolution?
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Comparative Analysis of Alternative Comparative Analysis of Alternative Mating StrategiesMating Strategies
•Conditional strategies in males are often
influenced feeding history and therefore
growth rate. •Strong sexual selection favors the evolution of
these traits.•However, trait
expression is widely divergent divergent among species.
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In Some Species,In Some Species,
SlowerSlower growing males mature
early as satellites.Males who cross a size threshold
continue to grow and mature later as territorials.
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In Other Species,In Other Species,
RapidlyRapidlygrowing males
become satellites, and
slower growers become
territorials.
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Comparative Analysis of Alternative Comparative Analysis of Alternative Mating StrategiesMating Strategies
The “comparative method” might work
reasonably well within closely related taxa
But it may lead to faulty faulty predictionspredictions in more
distantly related species
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In Particular,In Particular,1.Does natural selection occur
“overwhelmingly” at the individual level?
2. Are traits that evolve in one species likely to evolve in the same way in other species?
3. Does a “peculiarly direct” relationship exist between apparent selection and trait evolution?
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Correlated Responses to SelectionCorrelated Responses to Selection•The sign and magnitude of genetic correlations dodoinfluence influence the response to
selection.•Such correlations affect do affect both behavioral
and life history traits.•The response to
selection is not always “peculiarly direct.”
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Correlated Responses to SelectionCorrelated Responses to Selection
From Emlen 1996
Horn Length
Mat
urat
ion
time
Negative genetic correlations can
be common
They prevent “peculiarly direct”
responses to selection
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R = h2 S
Selectionintensity
Trait heritability
The response to selection = x
∆z = G β
parent parent parent parent offspring parent
offspring parent offspring offspring offspringoffspring
G G βG G β
z
z
∆ =
∆
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Genetic Correlations Must Be Known Genetic Correlations Must Be Known In Advance To Predict The Response In Advance To Predict The Response
to Selection to Selection (Wolf & Wade 2001)
From Walsh & Lynch 2000
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In Particular,In Particular,1.Does natural selection occur
“overwhelmingly” at the individual level?
2. Are traits that evolve in one species likely to evolve in the same way in other species?
3. Does a “peculiarly direct” relationship exist between apparent selection and trait evolution?
IT DEPENDSIT DEPENDS
NOT NECESSARILYNOT NECESSARILY
NONO
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Three ConsiderationsThree Considerations
a. How should fitness be measured?
b. Whose fitness is it?
c. Which interactions with social partners enhance or ameliorate
selection intensity?
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How IS Fitness Measured?How IS Fitness Measured?
A number of reliable sources suggest that
fitness should alwaysalways be measured within within
generationsgenerations.Arnold 1983; Lande & Arnold 1983; Cheverud
1984; Cheverud & Moore 1997; Wolf &
Wade 2001
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Why Does It Matter?Why Does It Matter?The number of offspring
parents produce measures the direct direct fitness of parents.
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CrossCross--Generation Fitness Measures Generation Fitness Measures
The intensity of selection diminishesdiminishes by ½ with each generation.
Selection intensity on sex limited traits is further further diminished.
Selection on conditional traits is diminished
further stillfurther still. 0
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1
self 1 2 3 4 5
Generation
Sele
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autosomalsex limitedconditional (50:50)conditional (10:90)
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Nevertheless, Nevertheless, A number of other
sources suggest that fitness can be measured
across generationsacross generations.
Clutton-Brock 1988; Drickamer et al. 2000; Veenet al. 2001; Neff & Pitcher
2005; Andersson & Simmons 2006; Gowaty &
Hubbell 2009.
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Three ConsiderationsThree Considerations
a. How should fitness be measured?
b. Whose fitness is it?
c. Which interactions with social partners enhance or ameliorate
selection intensity?
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Why Does It Matter?Why Does It Matter?Within-generation fitness is notnot confounded confounded with
other generations.It is notnot confoundedconfounded
with other traits.
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Confounding Fitness Across Confounding Fitness Across Generations Generations
Wolf and Wade 2001
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Confounding Traits Across Confounding Traits Across Generations Generations
Wolf and Wade 2001
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Confounding Traits Across Confounding Traits Across Generations Generations
Wolf and Wade 2001
= am(t-1) + em(t-1)
= ao(t) + eo(t)
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Three ConsiderationsThree Considerations
a. How should fitness be measured?
b. Whose fitness is it?
c. Which interactions with social partners enhance or ameliorate
selection intensity?
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Why Does It Matter?Why Does It Matter?Within each generation,
selection intensity is is influencedinfluenced by
environmental effects.
Therefore, the response to selection is unlikelyunlikely to
be “peculiarly direct.”
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When Is When Is Selection Selection
Enhanced or Enhanced or Reduced? Reduced?
It depends - on whether
environmental environmental variation variation acts to enhance or
reduce selection intensity.
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Selection: EnhancedSelection: EnhancedInteractions with
social partners can cause traits to be expressed more more
oftenoften than in usual, variable
environments.
Example: high density situations and cannibalism
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Selection: ReducedSelection: ReducedSocial partners may decreasedecrease the degree to which selection
is allowed to operate.
Example: maternal effects; the positivepositiveeffects of care can
ameliorateameliorate the effects of selection
on all progeny.
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Selection: ReducedSelection: Reduced
0
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Selection intensity on maternal traits is reduced in
daughters.
The expression of maternal care is sex limited, further
reducing selection intensity.
Genetic correlations between maternal and
offspring phenotypes are often negative.
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Selection: ReducedSelection: ReducedThe lek paradox?
Highly successful males are so
successful because their G x E is uniqueunique.
In another season, these conditions may
not exist.Only consistency among consistency among
environmentsenvironments allows selection intensity to remain
constant
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What Has Led To The Confusion?What Has Led To The Confusion?Sometimes the
important parameters DO line up and
Alexander’s Paradigm works.
Example: male male competition.
In other cases, it does not…
mate choicematernal effects
kin selected traitscorrelated traits
conditional traits.
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We Need to Think AboutWe Need to Think About
a. How is fitness measured?
b. Whose fitness is it?
c. Which interactions influence selection intensity?
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http://images.shoutwire.com/pic_full/5504796879097d1a-73c9-441e-a701-18f2cc4f3c21.JPG
Is STILL a Home Run!However, there are plenty of foul balls
hit the same way.
AlexanderAlexander’’s Home Runs Home Run