Developmentally defective genotype has 5 fates when mixed with developmentally proficient WT:

1. (Null Hypothesis, H1) Defector sporulates with same efficiency as in pure culture by itself.

2. Defector sporulation is worse than when by itself in pure culture.

3. Partial rescue (extracellular complementation), defector sporulates better in mixed culture than in pure culture by itself.

4. (Null Hypothesis, H2) Complete rescue to WT sporulation from crossfeeding complementation.

5.  Evolutionary cheating: defector produces more spores in presence of WT than WT levels (defector obtains disproportionate reproductive success)

 ExperimentsFirst

-6 populations of M. xanthus DK1622 were evolved for 1,000 generations under asocial conditions; one sporulation defective isolate from each pop was chosen

-each is mixed with WT

-5 of 6 isolates had higher spore production when mixed than in pure culture alone (partial complementation)

-those 5 were 10-fold rescued over pure culture

-the 1 of 6 not partially complemented had worse sporulation when mixed than in pure culture (fate #2)

-of the 5 partially complemented, 3 were cheaters (rescued to at least WT sporulation)

-2 of the cheaters were better than WT when rescued (when rare)

-One of the cheaters was almost completely defective at sporulation in pure culture, but as a minority was 50x greater at sporulating than WT

 Second

-The two evolved cheaters better than WT were mixed at 9 dif frequencies with WT

*As initial frequency increased, mixed culture sporulation output dropped below WT output (if in pure culture)

MEANING: cheaters harm group performance

 Third

-3 mutant genotypes of defined single mutations in signal production

-Question: Can the cheating phenotype arise from one mutation?  Or does it require multiple mutations?

-Answer: The phenotype can arise from one mutation, but that doesn’t mean that the evolved defectors have defects in the genes targeted.

I’ll admit that when I read a paper with a lot of numbers (as in the game matrices), my eyes kind of glaze over.  It takes some extra effort to figure out where the matrix numbers come from, and even though we discussed this in class, I’m still not extremely comfortable with the derivations: extrapolated numbers from a hypothetical portion of a line seem a little fishy.

Hesitations aside, in figure 1b (Nature, 1999), showing observed fitness values for a game in which opponents use conflicting strategies of cooperation and defection, the authors state that the realized payoff matrix for evolved high MOI phiH2 relative to phi6 ancestor shows evolution of an ESS of prisoner’s dilemma.  The lowest payoff is to the ancestor during co-infection; the ESS is to defect even though a higher pay-off occurs when phage cooperate.  This is said to be paradoxical, but in a way I think it makes sense if we give the cheater phage selfish characteristics: its fitness is lower when cooperating (0.65) with ancestor than with the ‘cheat:cheat’ scenario (0.83), so the logical ‘choice’ is to go the cheat:cheat way.

If the ‘cheaters’ were DI particles, the population would surely collapse without cooperators present.  Would the population survive if it were just evolved cheaters, though?  I think so, otherwise the cheat:cheat scenario would probably be zero…

I think that in class we all agreed that we need a theory-based method of bacterial taxonomy.  In the Cohan and Perry review, they propose a taxonomic system based on ecological and physiological characteristics.  Dave, Abe, and I talked about delineating species of bacteria by measuring rates of genetic recombination and HGT, along with whole genome comparisons.  It makes sense that ecotypes would have genes allowing them to persist in their ecological niche, giving them the same ecology, genetics, and function.  I think a system incorporating ecology, physiology, and genetics (including whole genome comparisons and rates of recombination, interbreeding), would be the most comprehensive method of taxonomy. 

Rates of recombination and HGT should be similar among ecotypes because they face the same environmental pressures, right?

Many of the concepts in this review are pretty new to me; I’m still trying to wrap my head around much of it.