Adaptive traits

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Adaptive traits

• What are they and how do we measure them?

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Question

• Can we reintroduce northern sea otters to Oregon?

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Question

• Can we reintroduce northern Sea Otters to Oregon?

Maximum likelihood tree based on microsatellites
Maximum likelihood tree based on mitochondrial DNA
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Genes vs the Environment

• Or nature versus nurture..
• Not an either or
• Both!
• VpVeVg

Environmental variance
Genetic variance
Phenotypic variance
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What is a quantitative trait?
Distribution of birth weight of babies (males
females) born to teenagers in Portland, Oregon,
in 1992
Also known as a fitness trait or an adaptive trait
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What is a quantitative trait?

• Quantitative traits are typically coded by many
  genes which interact with each other and with the
  environment

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Types of Quantitative traits

• Continuous traits
• continuum of phenotypes
• eg height, weight, milk yield
• Threshold traits
• present or absent based on underlying risk
• eg diabetes, schizophrenia, age at maturity,
  disease susceptibility
• Meristic traits
• discrete integral classes
• eg number off offspring, number of bristles on a
  fruitfly

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How do we study quantitative traits?

• 1. means and variances
• Mean
• Variance, a measure of the spread of the data

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Means and variances
Mean 571/10 57.1
Variance 112.9/9 12.54
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An understanding of variances

• Graphs showing three distributions with the same
  mean but different variances

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An understanding of the importance of means and
variances

• The mean and variance provides valuable
  information about the phenotypes of a group of
  individuals

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How do we partition variances between genes and
environment?
Case 1 We take genetically identical dandelion
seeds and put them in two different environments.
What explains the difference in the variance?
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How do we partition variances between genes and
environment?
!
Case 2 We take genetically identical and
genetically different dandelion seeds and put
them in the same environment. What explains the
difference in the variance?
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How do we study quantitative traits?

• 2. regression
• Regression between two variables is the slope of
  the line of best fit relating two variables

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How do we figure out the genetic component of a
quantitative trait?

• We study the transmission of a trait from one
  generation to the next

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Heritability

• Heritability h2 is the slope of the regression
  line between the mid parent and their offspring
• It is the proportion of a populations phenotype
  attributable to genetic factors

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Key Concept R h2S

• The heritability of a trait determines its
  potential for evolution
• Heritability is equivalent to heterozygosity at a
  single locus

x1
S x2 - xl
a. Distribution of parental phenotypes
S is the selection differential
x2
x3
b. Distribution of F1 phenotypes
R x3 - xl
R is the response to selection
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Heritability of quantitative traits in salmon
Trait
Species
Heritability
Reference
Weight
Coho
0.3 / 0.1
Hershberger et al 1990
Flesh color
Coho
0.30
Iwamoto et al. 1990
Early maturity
Chinook
0.3-0.5
Heath et al.1995
Age at maturity
Rainbow trout
0.2-0.7
Gjerde 1986
Disease resistance
Sockeye
0.27-0.38
McIntyre Amend 1978
Early Survival
Chinook
0 - 0.1
Withler et al. 1987
Anad. Migration
Pink
0.7-1.0
Smoker et al 1998
Spawning time
Rainbow trout
0.2-0.4
Gall et al. 1988
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Correlation between heterozygosity and
heritability

• Generally, not good.

Daphnia
Heterozygosity
Lynch et al 1989 and Lynch Spitze 1994
Lynch et al 1989 and Lynch Spitze 1994
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Quantitative vs Qualitative traits
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Why would we care about quantitative traits?

• Tells us about the processes that lead to
  adaptation, differentiation, speciation.

Original population
Frequency ofindividuals
Phenotypes (fur color)
Evolved population
Original population
Stabilizing selection
Diversifying selection
Directional selection
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Why would we care about quantitative traits?

• Really important in conservation
• Most characters of importance in conservation are
  fitness characters and are primarily quantitative
• Look at spawn timing
• in chinook salmon

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How can we impact adaptive traits?

• We can affect local adaptation by uncontrolled
  transplants

Even- and odd-year pink salmon
0.10
0.09
0.08
0.07
0.06
Survival rate
0.05
Pink salmon
0.04
0.03
0.02
Experiment
0.01
First
Second
0.00
F1 wild
F2 wild
F1 hybrid
F2 hybrid
F1 control
F2 control
After Gharret and Smoker, 1991 Gharret et al
1999
Group
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How can we impact adaptive traits?

• We can reduce variability in a fitness trait by
  inbreeding

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Why would we care about quantitative traits?

• Really important in aquaculture and agriculture!

Tilapia selected for growth
Tomatoes
Teosinte and Maize
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Why would we care about quantitative traits?

• Many diseases in humans have an environmental and
  genetic component

Atherosclerosis
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Question

• How do we use molecular markers to measure
  adaptive traits?

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Heritability

• Recall that we estimate heritability by examining
  correlation of traits between related
  individuals?
• Some species can exist as highly structured
  family groups in the wild
• Kinship studies can be used to estimate these
  relationships and we can then perform
  regressions to examine heritability of traits

Tree after Bentzen et al 2001, Heritability
estimates after Mousseau et al 1998
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Genome mapping
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Genome mapping
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QTL maps
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Whole sequences

• Recall that a quantitative trait is a result of
  an interaction between several genes and between
  genes and their environment
• If we know the whole sequence of an organism, we
  can study these interactions directly genomics.
• some whole sequences that are out there
• C.elegans (roundworms)
• Humans
• Drosphila (fruitfly)
• Fugu (pufferfish)
• Rice
• Many unicellular organisms

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Key Points

• Quantitative traits display a continuous
  distribution, and are the result of an
  interaction between many genes, and between these
  genes and the environment
• Nearly all fitness (or adaptive) traits are
  quantitative traits
• We study quantitative traits using statistics
  (means, variances, regressions)
• Heritability is a measure of the genetic
  component of a trait and provides important
  information on the potential of a trait for
  evolution

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Key Points

• An understanding of quantitative genetics
  principles is important in conservation,
  aquaculture and agriculture, and medicine
• Molecular approaches are increasingly providing a
  better understanding of
• heritability estimates in the wild
• the number of genes involved in quantitative
  traits,
• the interactions of these genes with each other
• the interactions of genes with the environment