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Modeling the unobservable developmental stability using a Bayesian latent variable model. Stefan van Dongen Dept. Biology, University of Antwerp. OUTLINE. Introduce biological problem developmental stability Develop statistical model Show some simulation results - PowerPoint PPT Presentation
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Modeling the unobservable developmental stability using a Bayesian latent variable model
Stefan van Dongen
Dept. Biology, University of Antwerp
OUTLINE
• Introduce biological problem– developmental stability
• Develop statistical model
• Show some simulation results
• Interesting results in humans– keep paying attention this is important
• 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
What is developmental stability?
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
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
How to estimate developmental stability? Measure asymmetry
• Asymmetry estimates the joint action of noise and stability
The picture is not so clearDirectional asymmetry or antisymmetry: adaptive and genetically determined
GynandromorphsNO STRESS EFFECT
The picture is not so clear
Subtle forms of asymmetry
Early action of stressContinuous scale
Phenodeviants & deformations
Under severe stress onlyBinary
Why study developmental stability?
Charles Darwin
EVOLUTION CONSERVATION BIOLOGY
FITNESS (reproductive success, survival, ….)
Difficult to measure in field
May be related to stabilityHigh stability => sufficient energy to achieve high fitness
Why study developmental stability?
Charles Darwin
EVOLUTION CONSERVATION BIOLOGY
FITNESS (reproductive success, survival, ….)
Difficult to measure in field
May be related to stabilityHigh stability => sufficient energy to achieve high fitness
INDIVIDUALLEVEL
1
2
3
Asymmetries are usually small:take bias due to measurement error into account
measure[i,j]~N(0,2ME)
DIRECTIONAL ASYMMETRY
FLUCTUATING ASYMMETRY
muind[i,j]=interc[i]+side[i,j] unb_FA[i]
where: interc[i]~N(0,2)and: unb_FA[i]~N(0,2
FA[i])
expected[i,j]=intercept+slopeside[i,j]
ERROR
unb_FA[i]~N(0,DI[i])
Assume DN to be constant
DS[i]~beta(1,2)
DI[i]=DN (1-DS[i])
The association between asymmetry and stability
N=500, 2500 and 5000DN constant, DS beta-distr.
‘good’ estimate of DSoverestimate of DN
‘worse’ estimate of DS‘good’ estimate of DN
‘failure’ to estimate bimodal pattern of DS
The association between asymmetry and stability
The association between asymmetry and stability
fitness[i]=interfit+slopefitDS[i]
The association between asymmetry and fitness
Further developments
• Multiple-trait analyses
• robustness against deviations of model assumptions (normality vs. log-normality)
• Include variation in DN (stochastic or constant)
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• …..
One case study