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Evolving strategies for life in an uncertain world Oana Carja - - PowerPoint PPT Presentation
Evolving strategies for life in an uncertain world Oana Carja - - PowerPoint PPT Presentation
Evolving strategies for life in an uncertain world Oana Carja University of Pennsylvania OSG All hands Meeting, March, 2017 the world inhabited by bacteria and other microorganisms is perilous. these tiny creatures must cope with the
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Environmental variation is commonplace yet unpredictable across biological systems from the adaptive immune system, the microenvironment in cancerous neoplasms, to populations of pathogens under drug pressure.
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Environmental variation is commonplace yet unpredictable across biological systems from the adaptive immune system, the microenvironment in cancerous neoplasms, to populations of pathogens under drug pressure. How do populations survive environmental stochasticity? How do they manage to persist and keep one's footing on an ever-changing landscape?
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Environmental variation is commonplace yet unpredictable across biological systems from the adaptive immune system, the microenvironment in cancerous neoplasms, to populations of pathogens under drug pressure. How do populations survive environmental stochasticity? How do they manage to persist and keep one's footing on an ever-changing landscape? Can organisms prepare for this environmental stochasticity?
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Can evolution prepare populations for this environmental stochasticity? Environmental variation is commonplace yet unpredictable across biological systems from the adaptive immune system, the microenvironment in cancerous neoplasms, to populations of pathogens under drug pressure. How do populations survive environmental stochasticity? How do they manage to persist and keep one's footing on an ever-changing landscape? Can organisms prepare for this environmental stochasticity?
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Image: Hubertus Beaumont
wrinkled and smooth P.fluorescens lines
“another rule which may prove useful can be derived from our theory. This is the rule that it is advisable to divide goods which are exposed to some danger into several portions rather than risk them all together”
Daniel Bernoulli, 1738
same genes, different phenotypes
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Image courtesy of Lauren Solomon, Broad Communications
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Figure: Rovira-Graells et al, Genome Research, 2014
the more transcriptionally diverse parasite adapted more rapidly to periodic changes in temperature meant to mimic periodic febrile episodes
more diverse less diverse
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phenotypic variance as an evolutionary strategy in uncertain environments
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bacterial persistence
Westfall and Levin, Biorxiv, 2016
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- 1. genetically identical populations, with two or more available phenotypes,
with each phenotype beneficial in a different environmental state
- 2. phenotypic states are partly heritable by offspring cells; rates of change
greater than genetic mutation
- 3. the rate of ’phenotypic mutation’ is itself under genetic control
(Levin and Rosen, 2006)
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- 1. genetically identical populations, with two or more available phenotypes,
with each phenotype beneficial in a different environmental state
- 2. phenotypic states are transient, partly heritable by offspring cells; rates of
change greater than genetic mutation
- 3. the rate of ’phenotypic mutation’ is itself under genetic control
(Levin and Rosen, 2006)
By tuning the rates at which variability is produced, populations may increase their long-term adaptability.
What is the evolutionary advantage of a phenotypically-plastic allele?
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population of A individuals
A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A
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population of A individuals
A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A
introduce one a individual
a-- a+
A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A a
phenotypic range of a allele
A a Genotype Phenotype
ф ф
A a
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population of A individuals
A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A
introduce one a individual
a-- a+
A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A a
phenotypic range of a allele
A a Genotype Phenotype
ф ф
A a
What is the fixation probability of an allele that increases phenotypic variability?
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population of A individuals
A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A
introduce one a individual
a-- a+
A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A a
phenotypic range of a allele
A a Genotype Phenotype
ф ф
A a
What is the fixation probability of an allele that increases phenotypic variability (or, alternatively, allele controlling variation in regulatory function at other protein-coding loci)?
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population of A individuals
A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A
introduce one a individual
a-- a+
A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A a
phenotypic range of a allele
p 1-p
a-- a+
ф
a
a
What is the fixation probability of an allele that increases phenotypic variability?
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population of A individuals
A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A
introduce one a individual
a-- a+
A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A a
phenotypic range of a allele
p 1-p
a-- a+
ф
a
a
What is the fixation probability of an allele that increases phenotypic variability? plasticity
parent - offspring correlation
genetic encoding partially heritable phenotype
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changing environments
Environment E1
A A a-- a+
ф
a
Environment E2
A a-- a+
ф
a
fittest phenotype in E1 is least fit in E2 increasing fitness
Environment E2 Environment E2 Environment E1
time
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Probability of fixation for the a allele Phenotypic memory
Environmental duration, n 5 7 10 15 20 25 30
0.0 0.1 0.2 0.3 0.00 0.25 0.50 0.75 1.00
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“adaptation in threatened populations is not like ordinary adaptation, it is a race against extinction”
(Maynard Smith, 1989)
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“adaptation in threatened populations is not like ordinary adaptation, it is a race against extinction”
(Maynard Smith, 1989) Day, 2005 Waxman and Gavrilets 2005 Willi et al.2006 Chapin et al. 2000 Schindler et al. 2010 Bijlsma and Loeschke 2012 Osmond and de Mazancourt 2013 Bell and Collins 2008 Sanjuan et al. 2010 Goldberg et al. 2012 Bock and Lengauer 2012 Gonzalez et al. 2013 Lindsey et al. 2013 Martin et al. 2013 Ramsayer et al. 2013 Carlson et al. 2014 Orr and Unckless 2014 World Health Organization 2014
conservation biology medical eradication
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population of A individuals
evolutionary rescue: one abrupt change in environment
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population of A individuals
A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A
introduce one a individual
a-- a+
A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A a
phenotypic range of a allele
p 1-p
a-- a+
ф
a
a
evolutionary rescue: one abrupt change in environment
A a Genotype Phenotype
ф
a
ф
A Birth rate
ф
A (1-N/K)
ф
a (1-N/K) Death rate 1 1
phenotypic memory:
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analytical intuition
a-- a+
ф
a
µ=(1-p)/2
mutation selection balance:
evolutionary dynamics of initial mutant with a beneficial phenotype
effective selective coefficient of a allele
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Memory Probability of evolutionary rescue
A B
Memory
0.0 0.1 0.2 0.3 0.00 0.25 0.50 0.75 1.00 0.000 0.005 0.010 0.015 0.020 0.025 0.00 0.25 0.50 0.75 1.00
Variance of a
0.16 0.09 0.04 0.02 0.01
evolutionary dynamics
- f initial mutant with
a beneficial phenotype Probability of evolutionary rescue Phenotypic memory Phenotypic memory evolutionary dynamics
- f initial mutant with
a deleterious phenotype analytical approximations simulations
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analytical intuition
a-- a+
ф
a
µ=(1-p)/2
mutation selection balance:
evolutionary dynamics of initial mutant with a beneficial phenotype
probability of switching to high fitness phenotype before loss: mutation as time-inhomogeneous Poisson process effective selective coefficient of a allele
evolutionary dynamics of initial mutant with a deleterious phenotype
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Memory Probability of evolutionary rescue
A B
Memory
0.0 0.1 0.2 0.3 0.00 0.25 0.50 0.75 1.00 0.000 0.005 0.010 0.015 0.020 0.025 0.00 0.25 0.50 0.75 1.00
Variance of a
0.16 0.09 0.04 0.02 0.01
evolutionary dynamics
- f initial mutant with
a beneficial phenotype Probability of evolutionary rescue Phenotypic memory Phenotypic memory evolutionary dynamics
- f initial mutant with
a deleterious phenotype analytical approximations simulations
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changing environments
Environment E1
A A a-- a+
ф
a
Environment E2
A a-- a+
ф
a
fittest phenotype in E1 is least fit in E2 increasing fitness
Environment E2 Environment E2 Environment E1
time
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500 1000 1500 2000 0.00 0.25 0.50 0.75 1.00
Duration in one environment, n
10 11 12 15
Time to extinction Phenotypic memory changing environments
Carja, Plotkin, bioRxiv, https://doi.org/10.1101/092718
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What does this mean for treatment strategies? Choose strategies that minimize probability of invasion and eventual fixation: effective interventions are treatments that disrupt the molecular memory to either extreme.
500 1000 1500 2000 0.00 0.25 0.50 0.75 1.00
There is an optimum phenotypic memory that maximizes fixation probability, evolutionary rescue, times to extinction of an invader allele with phenotypic variance.
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