In the Light of Evolution Volume V: Cooperation and Conflict (2011) / Chapter Skim
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5 Endemic Social Diversity Within Natural Kin Groups of a Cooperative Bacterium--SUSANNE A. KRAEMER and GREGORY J. VELICER
5 Endemic Social Diversity Within Natural Kin Groups of a Cooperative Bacterium--SUSANNE A. KRAEMER and GREGORY J. VELICER
Pages 91-116
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From page 91... ...
Eight of the 10 fruiting bodies were found to be internally diverse, with four exhibiting significant variation in social swarming phenotypes and five harboring large variation in the number of spores produced by member clones in pure culture. However, genetic variation within fruiting bodies was much lower than across fruiting bodies, suggesting that migration across even spatially proximate groups is limited relative to mutational generation of persisting endemic diversity.
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From page 92... ...
. Upon starvation, swarming cells aggregate and develop into multicellular fruiting bodies (Shimkets et al., 2006)
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From page 93... ...
, cell groups forming Myxococcus fruiting bodies are not expected to be entirely clonal owing to mutation.
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From page 94... ...
Ten natural fruiting body groups were harvested from soil collected at three Indiana woodland locations separated by several kilometers. Fruiting bodies from a given kilometer-scale location originated from centimeter-scale (MC fruiting bodies; see Methods)
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From page 95... ...
. Seven fruiting bodies did not exhibit significant within-group variation in swarming rate according to Kruskal-Wallis tests (P > 0.05)
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From page 96... ...
(B–D) Average swarming rates for individual clones from fruiting bodies KF3.2.8, KF4.3.9, and MC3.5.9, re spectively.
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From page 97... ...
. The isolates from fruiting bodies that harbored variation in spore production clustered into two distinct groups within each respective fruiting body by k-means cluster algorithms based on the criteria described in Methods.
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From page 98... ...
TABLE 5-1 Allelic and Phenotypic Variation Within and Across Fruiting Bodies 98 Swarm Spore Colony Gene pilA 0128 0176 0396 0533 4405 Fruiting Body Clone Rate # Color GH2.1.4 9 y 1 1 1 1 1 1 16 y 25 y 35 y 40 y 2 48 y GH3.5.6 2 y 2 2 2 2 1 2 11 y 22 y 3 36 y 2 40 y GH5.1.9 17 y 1 3 3 1 2 2 20 o 27 o 37 o Low 47 y KF2.4.9 10 y 4 2 4 3 3 3 17 y 21 y 38 y 42 y KF3.2.8 1 y 5 4 5 4 4 4 Fast 11 y Fast 12 y Fast 16 y 20 y Fast 26 y Fast 28 y
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From page 99... ...
Fast 29 y Fast 30 y 35 y Fast 37 y 39 y 45 y Fast 48 y Slow Low KF4.3.9 1 t 1 2 6 1 5 5 Slow Low 2 t 3 y 19 y Slow 23 y 28 y Slow Low 30 t 37 y Slow 40 y 2 44 y 1 Low KF5.4.6 4 y 6 1 7 5 6 6 11 y 28 y 29 y 36 y 1 MC3.1.9 3 y 7 5 2 1 1 5 16 y 25 y 28 y 47 y Low MC3.3.5 4 t 2 6 7 6 1 2 Low 8 y 2 9 y 16 y 1 21 y 99 continued
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From page 100... ...
. "Fast" and "Slow" designate individuals with minority swarming phenotypes in a given fruiting body, and "Low" designates individuals within low spore production clusters as identified by k-means cluster analysis (Methods)
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From page 101... ...
(B–D) Average spore production by individual clones from fruiting bodies KF4.3.9, MC3.3.5, and MC3.5.9, respec 101 tively.
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From page 102... ...
Seven pilA alleles were found across all clones (Table 5.1) , but only 5 of the 10 fruiting bodies harbored pilA polymorphisms, and no more than two pilA alleles were present in any fruiting body group.
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From page 103... ...
Fruiting bodies harbored no internal variation at these loci with the exception of MC3.3.5, which contained a single minority variant MC3.3.5c4. Posterior probabilities >90 and bootstrap values >70 (based on 1,000 bootstrap replicates)
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From page 104... ...
DISCUSSION The genetic and social diversity pervading natural Myxococcus populations is highly structured across local social groups within which cooperative -- and likely antagonistic -- interactions occur. This study and others have together shown that representatives of distinct but spa tially proximate fruiting body groups vary starkly in social motility (Fig.
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From page 105... ...
xanthus. In phase variation, bacterial cells switch b etween discrete phenotypic states at much higher rates than would be generated by the genomewide average mutation rate (Laue and Gill, 1994, 1995; Beaumont et al., 2009)
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From page 106... ...
Colonies derived from the other three parental clones selected for the control experiments showed no variation for any visual phenotype. Thus, exhibition of phase variation is itself yet another phenotype that seems to vary among closely related groupmates within natural fruiting bodies.
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From page 107... ...
Limitation of Socially Defective Cheaters Cheater strains with social defects in clonal groups that can exploit cooperative genotypes in mixed groups during Myxococcus development readily appear by mutation in laboratory populations (Velicer et al., 2000)
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From page 108... ...
Only mutations creating socially defective cheaters that have an advantage within a group across an organism's entire life cycle will increase substantially within groups. The mutation rate to cheaters that have such a net within-group advantage (at least when rare)
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From page 109... ...
. Alternatively, if the combination of mutation rate to socially defective cheaters and i ntergroup cheater migration is sufficiently high relative to the rate of cheater loss via among-group selection, all social groups in a meta population could become infected by cheaters.
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From page 110... ...
Finally, Myxococcus social diversity may be maintained by various forms of balancing selection. Within kin groups, frequency-dependent selection might maintain both cooperators and socially defective cheaters (Velicer et al., 2000)
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From page 111... ...
The relative roles that the fundamental forces of evolution -- mutation, distinct forms of selection, migration, genetic drift, and recombination -- play in shaping natural social variation in the myxobacteria remain to be quantified. Doing so will require estimation of mutation rates, identification of loci and alleles responsible for observed social variation, screening for population genetic signatures of distinct evolutionary forces, and characterization of fitness relationships among social interactants under conditions relevant to natural habitats.
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From page 112... ...
Fruiting bodies from the GH and KF locations examined here were isolated from soil particles separated by meters in the sample plot, whereas the soil particles from which the MC fruiting bodies were isolated were from the same centimeter-scale plot because soil from other locations along the meter-scale transect did not yield fruiting bodies. Swarming Motility Assays Cells from all 48 clones representing each isolated fruiting body were inoculated from frozen stocks into 8 mL CTT liquid and incubated for 3 or 4 days.
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From page 113... ...
were performed in at least three temporarily independent replicate blocks. Sporulation Assays Five clones each were assayed for spore production from fruiting bodies that did not exhibit variation in swarming rate or other motility phenotypes.
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, one cycle of development on TPM agar followed by heat and sonication treatments and subsequent growth again in CTT liquid prior to being diluted into CTT soft agar to allow isolation of clones for phenotypic analysis. Forty-eight clones from each initially clonal culture were isolated at random and examined for variation in swarming motility rate and phenotype as well as variation in fruiting body phenotypes after 10 µL of culture (5 × 109 cells/mL)
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From page 115... ...
Hanschen and M Toups for helpful suggestions regarding statistical and phylogenetic analyses.
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