Joan Strassmann, "Evolution of cooperation and control of

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Alleles held at 

equilibrium by 

balancing selection 

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Neutral mutation 

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Lost by drift

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Lost by drift 

Increased 

by drift

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balancing selection

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balancing selection

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balancing selection

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balancing selection

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balancing selection

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balancing selection

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Minority neutral variants 

Favorable mutation

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selection 

Minority neutral variants 

Favorable mutation

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TgrB1 -- 226 polymorphic positions (n=30) 

N sig seq 

Ig-1 Ig-2 Ig-3 TM C 

TgrC1 -- 319 polymorphic positions (n=29) 

N sig seq Ig-1 Ig-2 Ig-3 Ig-4 Ig-5 Ig-6 

TM C 

Benabentos et al., 2009 Current Biol. 19(7):567-72. 

Immunoglobulin-like domain

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TgrD1 -- 9 polymorphic positions out of 15 wild strains 

TgrE1 --10 polymorphic positions out of 6 wild strains 

Benabentos et al., 2009 Current Biol. 19(7):567-72.

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Genetic distance from AX4 

Microsatellite-based 

r = 0.773 

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qRT-PCR profile in Ax4 

Ax4 

tgrB1 - 

tgrC1 - 

12h 

17h 

0.5mm

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Kin recognition suggests 

that cheating was 

important 

Prediction: 

If ability to cheat is a part 

of evolved fitness, then 

that ability should 

decline when selection is 

removed and drift 

increased.

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Sara Fox 

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Control lines do compete evenly against 

ancestor 

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control line 

Ancestor-gfp 

Percent change of evolved lines compared to ancestor

Mutation accumulation lines highly variable; 

tend to lose against ancestor 

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MA line 

Ancestor-gfp 

Percent change of evolved lines compared to ancestor

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Sequence another species for comparison 

Schaap et al. 2006 Science

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Xiangjun Tian

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Kuzdzal-Fick, Fox, Strassmann & Queller, Science 334:1548

Select for success of new natural 

cheater mutants under low 

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relatedness 

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Kuzdzal-Fick

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Cooperation is often treated as a 

topic apart, but it is basic to the 

evolution of life

In the major transitions in evolution, 

conflict must be resolved for formerly 

independent units to become selected 

together 

John Maynard Smith, Eörs Sathmáry 

Chromosome Prokaryote Eukaryote Multicellular 

Cell 

Cell 

Organism 

Colonial 

Superorganism

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High cooperation among parts, Low actual conflict among parts 

Consolidation of adaptations making the organism a unit of near unanimous 

design 

Queller & Strassmann 2009. Phil. Trans. R. Soc.,Strassmann & Queller 2010. Evolution

1. What are the possible fitness 

benefits to grouping?

1. What are the possible fitness 

benefits to grouping?

1 a. Rise above the hazards of the soil, 

dispersal is facilitated

Distance 

travelled 

(cm) 

1b. Larger groups move farther 

8 

7 

6 

5 

4 

3 

2 

1 

0 

0 1 2 3 4 5 6 

Slug size 

(total volume of spores producted mm 3 ) 

Spearman rank correlation, 

p

Dicty slugs 

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Bacteria slurry 

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1d. Exploit other cells to make 

better spores 

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2a. Exploitation by some clones 

avoiding the sterile, altruist role 

of stalk 

For 12 mixtures, we genotyped the head and tail of 

7 individual slugs from each plate (Strassmann et 

al. Nature, 2000)

Within 2-clone chimeras, in 6/12 mixes 

one contributes more to spore than to stalk 

clone 1 clone 2 

NC60.1 

NC105.1 

NC28.1 

NC63.2 

NC98.1 

NC101.1 

NC94.2 

NC85.1 

NC75.2 

NC4 

NC34.1 

NC85.2 

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T 

0.0 0.2 0.4 0.6 0.8 1.0 

Proportion of clone 1 

NC60.2 

NC34.1 

NC28.2 

NC69.1 

NC70.1 

NC99.1 

NC94.1 

NC85.2 

NC28.1 

NC47.2 

NC34.2 

NC39.1 

% clone 1 % clone 2 

Spores : top bar 

Stalk : bottom bar 

Neutral Prediction: 

1 2 

0.0 0.2 0.4 0.6 0.8 1.0 

Strassmann, Zhu, and 

Queller, Nature, 2000

Within 2-clone chimeras, in 6/12 mixes 

one contributes more to spore than to stalk 

clone 1 clone 2 

NC60.1 

NC105.1 

NC28.1 

NC63.2 

NC98.1 

NC101.1 

NC94.2 

NC85.1 

NC75.2 

NC4 

NC34.1 

NC85.2 

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0.0 0.2 0.4 0.6 0.8 1.0 

Proportion of clone 1 

NC60.2 

NC34.1 

NC28.2 

NC69.1 

NC70.1 

NC99.1 

NC94.1 

NC85.2 

NC28.1 

NC47.2 

NC34.2 

NC39.1 

% clone 1 % clone 2 

Spores : top bar 

Stalk : bottom bar 

Neutral Prediction: 

1 2 

0.0 0.2 0.4 0.6 0.8 1.0 

Strassmann, Zhu, and 

Queller, Nature, 2000

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2b. Cells that have starved 4 hours are more likely 

to become spores 

Random 

Stalk 

Spores 

Kudzdal-Fick et al. Biology Letters 2010 

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*Fisher’s PLSD p

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Huang et al. 1997

2c. Do chimeras move as far 

as pure clones?

Mean distance migrated (cm) 

5 

4 

3 

2 

1 

0 

Chimaeric slugs move less far 

1 2 5 10 

Number of clones in slug 

10 different single clones 

10 different clone pairs 

1 mix of five clones (5 reps) 

1 mix of ten clones (5 reps) 

N=30, ANOVA, p

2c. Chimeras move less far 

than pure clones, for a given 

number of cells 

Foster et al., Royal Society Proceedings B, 2002 

Kevin Foster 

Angelo Fortunato

There are benefits and costs to 

grouping, making this an excellent 

system for studying sociality

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isolates� 

clones� 

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Genetic distance from AX4 

Microsatellite-based 

r = 0.773 

P

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5. How common are genes 

involved in cheating?

Great molecular biology collaborators 

Adam Kuspa Gadi Shaulsky

Do a selection on a pool of 

insertion mutants.

Does the interaction affect life history 

traits? 

Non-farmer 

Fb’s: 

Farmer 

5 days of development 

Fb’s: Bacteria 

3 mm 

Farmer clones enter the social stage 

before all food is exhausted 

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Dicty gene 

Blasticidin 

BamHI 

Bs R 

pBSR1 

4.10 Kb 

REMI knockouts 

Amp R 

DpnII 

linearize plasmid and insert 

into random spot in Dicty 

Ampicillin

Selection to find cheater mutations 

10,000 REMI generated 

mutants 

1 round 

SM plate SM plate

Select for cheaters that get into 

spores instead of stalk 

Generation 1 

Generation 20

Selected 

population 

Test for cheating 

mix 1:1 with wildtype AX4, 

labeled with green flourescent protein 

AX4 

GFP

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Santorelli et al. Nature, 2008

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Dictyostelium discoideum as a social organism 

1. Benefits to grouping 

2. Costs to grouping 

3. Relatedness and kin discrimination 

4. Experimental evolution: Impact of 

low relatedness 

5. Genes involved in cheating are 

common and show rapid evolution.

In the lab, on agar and on soil, 

clones mix readily.

1) Is the farming trait stable? 

Dictyostelium discoideum 

Bacteria 

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Farmers regain their association with bacteria 

after curing with antibiotics; non-farmers do not 

acquire an association 

% 

Reassociation 

100 

80 

60 

40 

20 

0 

Farmers Non-farmers 

10 random sori; 4 farmers and 4 non-farmers; 

F 1,6 =48.864, p

% occurrence 

2a) What proportion of clones are farmers? 

100 

80 

60 

40 

20 

0 

5/14 

3/9 

Virginia 

1/3 

Minnesota 

Farmers and partners isolated from 4 independent collections of soil samples 

4/9 

Non-farmer 

Farmer 

Average 

proportion 

of farmers 

35.5%

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94 

99 

99 

96 

93 

QS8 

QS21 

QS14 

QS11 

QS18 

QS22 

QS15 

QS9 

QS23 

disc NW 001852778 

QS4 

QS1 

QS12 

QS6 

QS17 

citr DQ340385

Joan Strassmann, "Evolution of cooperation and control of

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