Transcript Pseudomonas aeruginosa

Individual-based models of social evolution
in biofilms
Sara Mitri
@ the Foster lab
Department of Zoology
University of Oxford
Who am I?
MSc thesis: “The co-evolution of language and behaviour in robots”
PhD thesis: “The evolution of communication in robot societies”
Postdoc proposal: “Spatial patterns and social evolution in bacterial biofilms”
What questions am I interested in?
General
How does evolution shape social behaviour?
How does evolution shape social behaviour
in microbial biofilms?
What role do ecological
factors play in the
evolution of social
phenotypes in
microbial biofilms?
Specific
How do spatial patterns in
microbial biofilms
influence selection for
social phenotypes?
How does one combine
theoretical and
experimental methods to
answer these questions?
How does the presence of
other species in microbial
biofilms influence selection
for social phenotypes?
What technology do I use?
Individual-based models
Lab experiments
How do spatial patterns in microbial biofilms
influence selection for social phenotypes?
Picioreanu et al. (2004) Appl & Env Microbiol
Xavier et al. (2005) Env Microbiol
1.
Low nutrient concentration
High nutrient concentration
Nadell et al. (2010) PLoS Comp Biol
The thickness of the
growing edge
Nadell et al. (2010) PLoS Comp Biol
2.
Secretes (costly) beneficial product
Does not secrete beneficial product
Low nutrient concentration
High nutrient concentration
Nadell et al. (2010) PLoS Comp Biol
Experiments using Pseudomonas aeruginosa
How does the presence of other species in microbial
biofilms influence selection for social phenotypes?
1. “Towers” are no longer
sufficient to give an
advantage to secretors.
2. Other species can
insulate secretors from
non-secretors, giving them
an advantage.
Mitri et al. (in press) PNAS
3. Mutualistic secretions seem
unlikely to be selected for.
Mitri et al. (in press) PNAS
Motivation
Challenges
Opportunities
Thanks go to…
Carey Nadell
Nuno Oliveira
Jonas Schluter
Marina Caldara
Kevin Foster
João Xavier
Wook Kim
Experiments using Pseudomonas aeruginosa
One species
Two species
One species
Two species
Two species
(species 2 benefits
from secretions)
Two species
(species 2 does not
benefit from secretions)
Two species
(species 2 benefits
from secretions)
Two species
(species 2 does not
benefit from secretions)
Why do secretors do so badly
in the presence of other species
under low nutrient conditions?
Hypothesis: competition during initial growth phase
Reducing competition
Reducing competition
3 questions
1. How do secretors and non-secretors fare
in the presence of other species?
Secretors can be outcompeted by non-secretors
due to increased initial competition.
3 questions
2. How do secretors and non-secretors fare
in the presence of many other species?
Equal proportions
of species 1 and 2
Species 2 is initially
9 times more abundant
than species 1
Equal proportions
of species 1 and 2
Species 2 is initially
9 times more abundant
than species 1
Why does the abundance of other species
provide an advantage to secretors over non-secretors?
Hypothesis: other species insulate secretors
Measuring segregation
3 questions
2. How do secretors and non-secretors fare
in the presence of many other species?
Secretors can outcompete non-secretors
when competition is low (e.g., high nutrients)
because other species can separate the two phenotypes.
3 questions
3. How do secretors and non-secretors fare
if other species are mutualistic partners?
Mutualism between
2 species
with self-benefit
Mutualism between
2 species
without self-benefit
Mutualism between
2 species
with self-benefit
Mutualism between
2 species
without self-benefit
Why does mutualism not work?
Hypothesis:
when cell types are segregated,
secretors and species 2 cannot benefit from each other;
when cell types are mixed, non-secretors benefit
Explaining mutualism
Low nutrients
Secretors
Species 2
High nutrients
Non-secretors
Species 2
Secretors
Species 2
Non-secretors
Species 2
Explaining mutualism
3 questions
3. How do secretors and non-secretors fare
if other species are mutualistic partners?
Secretors do not do well compared to non-secretors
because conditions that favour mutualistic interactions
also maximize benefits of non-secretors.
A case where mutualism “works”
A case where mutualism “works”
3 questions
1. How do secretors and non-secretors fare
in the presence of other species?
2. How do secretors and non-secretors fare
in the presence of many other species?
3. How do secretors and non-secretors fare
if other species are mutualistic partners?
3 answers
Secretors can be outcompeted by non-secretors
due to increased initial competition.
Secretors can outcompete non-secretors
when competition is low (e.g., high nutrients)
because other species can separate the two phenotypes.
Secretors do not do well compared to non-secretors
because conditions that favour mutualistic interactions
also maximize benefits of non-secretors.
Not taken into consideration
(i.e. future work)
By-product mutualisms
Competition among groups
Regulation of social behaviour
Competition between species
Niche overlap
Relative fitness of
secretors to non-secretors