Relationships between Relative Mixing Effect <i>(C_ij)</i> or Predicted Relative Performance <i>(W*_ij)</i> (<i>y</i>-Axis) and Actual Relative Performance (<i>W_ij</i>) (<i>x</i>-Axis)

<p>Relationships between Relative Mixing Effect <i>(C_ij)</i> or Predicted Relative Performance <i>(W*_ij)</i> (<i>y</i>-Axis) and Actual Relative Performance (<i>W_ij</i>) (<i>x</i>-Axis)</p

Bidirectional Mixing Effects for Strains A, B, and G against All Competitors

<p>The log-scale effect of mixing strains <i>i</i> and <i>j</i> on the sporulation efficiency of strain <i>i</i> is given as <i>C_i</i>(<i>j</i>). Open bars show the effect of mixing on sporulation efficiency for strains A (A), B (B), and G (C) in response to each competitor shown along the horizontal axis. Shaded bars indicate the effect of mixing on the sporulation of the variable competitors. Error bars indicate 95% confidence intervals.</p

Distribution of Mixing Effects on the Sporulation Efficiencies of Individual Competitors (C<i>_i</i>[<i>j</i>])

<p>Distribution of Mixing Effects on the Sporulation Efficiencies of Individual Competitors (C<i>_i</i>[<i>j</i>])</p

Effects of Pairwise Mixing on Fruiting Body Size and Distribution

<p>Pairings AE, DH, AF, and BE are shown. Pure-culture fruiting bodies are shown in the top and middle photographs of each column (first and second listed strains, respectively), and fruiting bodies of the corresponding mixed culture are shown at the bottom.</p

Extinction Caused by Mutual Antagonism between Strains E and F

<div><p>(A) At an initial developmental density of 10⁹ cells/ml, no spores survived starvation in mixed populations, but both competitors performed well in clonal isolation. Error bars indicate 95% confidence intervals.</p> <p>(B) Developmental phenotypes of E and F in pure culture (left and right, respectively) and in mixed competition (middle).</p></div

Nair,Fiegna&Velicer_methods_tables_figures_ESM.pdf from Indirect evolution of social fitness inequalities and facultative social exploitation

Microbial genotypes with similarly high proficiency at a cooperative behaviour in genetically pure groups often exhibit fitness inequalities caused by social interaction in mixed groups. Winning competitors in this scenario have been referred to as ‘cheaters’ in some studies. Such interaction-specific fitness inequalities, as well as social exploitation (in which interaction between genotypes increases absolute fitness), might evolve due to selection for competitiveness at the focal behaviour or might arise non-adaptively due to pleiotropy, hitchhiking or genetic drift. The bacterium <i>Myxococcus xanthus</i> sporulates during cooperative development of multicellular fruiting bodies. Using <i>M. xanthus</i> lineages that underwent experimental evolution in allopatry without selection on sporulation, we demonstrate that interaction-specific fitness inequalities and facultative social exploitation during development readily evolved indirectly among descendant lineages. Fitness inequalities between evolved genotypes were not caused by divergence in developmental speed, as faster-developing strains were not over-represented among competition winners. In competitions between ancestors and several evolved strains, all evolved genotypes produced more spores than the ancestors, including losers of evolved-versus-evolved competitions, indicating that adaptation in non-developmental contexts pleiotropically increased competitiveness for spore production. Overall, our results suggest that fitness inequalities caused by social interaction during cooperative process may often evolve non-adaptively in natural populations

Nair,Fiegna&Velicer_methods_tables_figures_ESM.pdf from Indirect evolution of social fitness inequalities and facultative social exploitation

Microbial genotypes with similarly high proficiency at a cooperative behaviour in genetically pure groups often exhibit fitness inequalities caused by social interaction in mixed groups. Winning competitors in this scenario have been referred to as ‘cheaters’ in some studies. Such interaction-specific fitness inequalities, as well as social exploitation (in which interaction between genotypes increases absolute fitness), might evolve due to selection for competitiveness at the focal behaviour or might arise non-adaptively due to pleiotropy, hitchhiking or genetic drift. The bacterium <i>Myxococcus xanthus</i> sporulates during cooperative development of multicellular fruiting bodies. Using <i>M. xanthus</i> lineages that underwent experimental evolution in allopatry without selection on sporulation, we demonstrate that interaction-specific fitness inequalities and facultative social exploitation during development readily evolved indirectly among descendant lineages. Fitness inequalities between evolved genotypes were not caused by divergence in developmental speed, as faster-developing strains were not over-represented among competition winners. In competitions between ancestors and several evolved strains, all evolved genotypes produced more spores than the ancestors, including losers of evolved-versus-evolved competitions, indicating that adaptation in non-developmental contexts pleiotropically increased competitiveness for spore production. Overall, our results suggest that fitness inequalities caused by social interaction during cooperative processes may often evolve non-adaptively in natural populations

Statistical analysis of <i>M</i>. <i>xanthus</i> growth data.

Linear model and Type III ANOVA for M. xanthus growth data using P. fluorescens inoculum size, temperature treatment, their interaction, and time as explanatory variables. Post hoc contrasts between inoculum sizes are computed for each temperature–time combination. (PDF)</p

<i>P</i>. <i>fluorescens</i> kills <i>M</i>. <i>xanthus</i> when both species are pregrown and interact at 22°C but not when both are pregrown and interact at 32°C.

DK3470 population sizes are shown 24 hours after interaction with P. fluorescens when the 2 species interact at the same temperature at which both had been reared prior to interaction. Means of log10-transformed CFU + 1 values and 95% confidence intervals are shown. Lighter dots are biological replicates (n = 3). *** p M. xanthus population size after interaction with P. fluorescens (green dots) vs. in the control treatment (black dots) when the 2 species were reared and interacted at 22°C. The dataset for this figure and the R script used to analyze it and make the figure are available on Zenodo (10.5281/zenodo.10214013). (PDF)</p

<i>M</i>. <i>xanthus</i> swarming through <i>P</i>. <i>fluorescens</i> lawns depends on the temperature of <i>P</i>. <i>fluorescens</i> growth prior to predator–prey interaction.

Swarm diameters of 3 M. xanthus genotypes (rows) after 7 days on M9cas agar bearing either a lawn of one of several prey species (green dots) or no prey (black dots). Prey lawns were incubated at 12, 22, or 32°C for 22 hours and then brought to room temperature for 2 hours before M. xanthus was added. Small dots are biological replicates (n = 3 except for R. vitis for which n = 2), and error bars represent 95% confidence intervals about the means (big dots). Significant differences between average diameters of swarms on prey grown at different temperatures are shown; ** p p < 0.001 (Tukey-adjusted contrasts). The dataset for this figure and the R script used to analyze it and make the figure are available on Zenodo (10.5281/zenodo.10214013).</p