Modeling the unobservable developmental stability using a Bayesian latent variable model

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Modeling the unobservable developmental stability
using a Bayesian latent variable model

• Stefan van Dongen
• Dept. Biology, University of Antwerp

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OUTLINE

• Introduce biological problem
• developmental stability
• Develop statistical model
• Show some simulation results
• Interesting results in humans
• keep paying attention this is important

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What is developmental stability?

• We develop from 1 cell to what we are now
• During development mistakes occur due to random
  noise (DN)
• Fluctuations in concentrations
• Somatic mutations
• Death of cells
• There are mechanisms that correct for these
  mistakes DEVELOPMENTAL STABILITY

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What is developmental stability?

• Our genotype and environment in which we live
  determine our size and shape
• unknown in most cases
• BUT there is some degree of stochasticity
• PROBLEM how to estimate this stochastic
  contribution which has two components (noise and
  stability)
• SOLUTION Look at symmetric traits

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How to estimate developmental stability?

• Left and right side develop often under exactly
  the same environmental conditions (but e.g.
  handedness) and obviously share the same genotype
• In the absence of noise they should develop to
  the same size or shape
• Noise will cause asymmetry
• Stability will counteract this effect

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How to estimate developmental stability? Measure
asymmetry

• Asymmetry estimates the joint action of noise and
  stability

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The picture is not so clear
NO STRESS EFFECT
Directional asymmetry or antisymmetry adaptive
and genetically determined
Gynandromorphs
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The picture is not so clear
Early action of stress Continuous scale
Under severe stress only Binary
Subtle forms of asymmetry
Phenodeviants deformations
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Why study developmental stability?
Charles Darwin
EVOLUTION
CONSERVATION BIOLOGY
FITNESS (reproductive success, survival, .)
Difficult to measure in field May be related to
stability High stability gt sufficient energy to
achieve high fitness
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Why study developmental stability?
INDIVIDUAL LEVEL
Charles Darwin
EVOLUTION
CONSERVATION BIOLOGY
FITNESS (reproductive success, survival, .)
Difficult to measure in field May be related to
stability High stability gt sufficient energy to
achieve high fitness
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Asymmetries are usually smalltake bias due to
measurement error into account
FLUCTUATING ASYMMETRY
muindi,jintercisidei,j ?unb_FAi where
interciN(0,?2) and unb_FAiN(0,?2FAi)
expectedi,jinterceptslope?sidei,j
DIRECTIONAL ASYMMETRY
measurei,jN(0,?2ME)
ERROR
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(No Transcript)
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The association between asymmetry and stability
unb_FAiN(0,DIi)
Assume DN to be constant
DIiDN? (1-DSi)
DSibeta(?1,?2)
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The association between asymmetry and stability
N500, 2500 and 5000 DN constant, DS beta-distr.
good estimate of DS overestimate of DN
worse estimate of DS good estimate of DN
failure to estimate bimodal pattern of DS
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The association between asymmetry and stability
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The association between asymmetry and fitness
fitnessiinterfitslopefit?DSi
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Further developments

• Multiple-trait analyses
• robustness against deviations of model
  assumptions (normality vs. log-normality)
• Include variation in DN (stochastic or constant)

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Interesting results in humans

• Symmetric persons have higher IQ
• Criminals have higher asymmetry
• Symmetric males and females are more attractive
• Symmetric males have more sexual partners in
  their life
• Symmetric males are better lovers
• Female breast asymmetry decreases around period
  of ovulation
• Females are more selective for symmetric males
  around this ovulation period
• ..

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One case study