Individual-based models of social evolution in biofilms

Sara Mitri

@ the Foster labDepartment of ZoologyUniversity of Oxford

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”

Who am I?

How does evolution shape social behaviour?

What questions am I interested in?

How does evolution shape social behaviour in microbial biofilms?

How does one combine theoretical and

experimental methods to answer these questions?

What role do ecological factors play in the evolution of social

phenotypes in microbial biofilms?

How do spatial patterns in microbial biofilms

influence selection for social phenotypes?

General

Specific

How does the presence of other species in microbial

biofilms influence selection for social phenotypes?

What technology do I use?

Lab experimentsIndividual-based models

How do spatial patterns in microbial biofilms influence selection for social phenotypes?

Picioreanu et al. (2004) Appl & Env MicrobiolXavier 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.

Low nutrient concentration High nutrient concentration

Secretes (costly) beneficial productDoes not secrete beneficial product

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…

Kevin Foster

Carey NadellNuno OliveiraJonas SchluterMarina Caldara

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 badlyin the presence of other species under low nutrient conditions?

Hypothesis: competition during initial growth phase

Reducing competition

Reducing competition

1. How do secretors and non-secretors farein the presence of other species?

Secretors can be outcompeted by non-secretorsdue to increased initial competition.

3 questions

2. How do secretors and non-secretors farein the presence of many other species?

3 questions

Equal proportionsof species 1 and 2

Species 2 is initially9 times more abundant

than species 1

Equal proportionsof species 1 and 2

Species 2 is initially9 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

2. How do secretors and non-secretors farein the presence of many other species?

Secretors can outcompete non-secretorswhen competition is low (e.g., high nutrients)

because other species can separate the two phenotypes.

3 questions

3. How do secretors and non-secretors fareif other species are mutualistic partners?

3 questions

Mutualism between2 species

with self-benefit

Mutualism between2 species

without self-benefit

Mutualism between2 species

with self-benefit

Mutualism between2 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

Non-secretors Species 2

High nutrients

Secretors Species 2

Non-secretors Species 2

Explaining mutualism

3. How do secretors and non-secretors fareif other species are mutualistic partners?

3 questions

Secretors do not do well compared to non-secretorsbecause conditions that favour mutualistic interactions

also maximize benefits of non-secretors.

A case where mutualism “works”

A case where mutualism “works”

3. How do secretors and non-secretors fareif other species are mutualistic partners?

3 questions

2. How do secretors and non-secretors farein the presence of many other species?

1. How do secretors and non-secretors farein the presence of other species?

3 answers

Secretors do not do well compared to non-secretorsbecause conditions that favour mutualistic interactions

also maximize benefits of non-secretors.

Secretors can outcompete non-secretorswhen competition is low (e.g., high nutrients)

because other species can separate the two phenotypes.

Secretors can be outcompeted by non-secretorsdue to increased initial competition.

Not taken into consideration(i.e. future work)

Niche overlapCompetition between speciesRegulation of social behaviour

Competition among groupsBy-product mutualisms

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