Chimaeric load among sympatric social bacteria increases with genotype richness

Abstract

The total productivity of social groups can be determined by interactions among their constituents. Chimaeric load—the reduction of group productivity caused by antagonistic within-group heterogeneity—may be common in heterogeneous microbial groups due to dysfunctional behavioural interactions between distinct individuals. However, some instances of chimaerism in social microbes can increase group productivity, thus making a general relationship between chimaerism and group-level performance non-obvious. Using genetically similar strains of the soil bacterium Myxococcus xanthus that were isolated from a single centimetre-scale patch of soil, we tested for a relationship between degree of chimaerism (genotype richness) and total group performance at social behaviours displayed by this species. Within-group genotype richness was found to correlate negatively with total group performance at most traits examined, including swarming in both predatory and prey-free environments and spore production during development. These results suggest that interactions between such neighbouring strains in the wild will tend to be mutually antagonistic. Negative correlations between group performance and average genetic distance among group constituents at three known social genes were not found, suggesting that divergence at other loci that govern social interaction phenotypes is responsible for the observed chimaeric load. The potential for chimaeric load to result from co-aggregation among even closely related neighbours may promote the maintenance and strengthening of kin discrimination mechanisms, such as colony-merger incompatibilities observed in M. xanthus . The findings reported here may thus have implications for understanding the evolution and maintenance of diversity in structured populations of soil microbes.

Kin discrimination between sympatric Bacillus subtilis isolates

“…In social settings, within-group genotype richness was found to correlate negatively with group performance, such as swarming in M. xanthus (40), and neighboring strains thus tend to be antagonistic. In the amoeba Dictyostelium discoideum, fruiting bodies composed preferentially of kin cells promote cooperation during multicellular development (8,9).…”

Coral chimerism as an evolutionary rescue mechanism to mitigate global climate change impacts

“…In corals, the few cases of chimerism‐borne costs reveal only morphological absorption of chimeric participants (Barki et al, ; Boschma, ), a phenomenon not recorded in naturally growing chimeras of other invertebrates (such as tunicates) growing in the field, reflecting a distensible strategy of fused genotypes depending on environmental conditions (Chadwick‐Furman & Weissman, ). Costs on the coral chimeric size were also suggested (Amar et al, ), as “chimeric‐load” in social bacteria, the reduction in group productivity caused by antagonistic within‐group heterogeneity (Foster, Fortunato, Strassmann, & Queller, ; Mendes‐Soares, Chen, Fitzpatrick, & Velicer, ). Chimeras in few other taxa of marine invertebrates (such as sponges and tunicates) revealed that costs or benefits for chimerism could not be elucidated.…”

“…Costs on the coral chimeric size were also suggested (Amar et al, 2008), as "chimeric-load" in social bacteria, the reduction in group productivity caused by antagonistic within-group heterogeneity (Foster, Fortunato, Strassmann, & Queller, 2002;Mendes-Soares, Chen, Fitzpatrick, & Velicer, 2014). Chimeras in few other taxa of marine invertebrates (such as sponges and tunicates) revealed that costs or benefits for chimerism could not be elucidated.…”

Why Aggregate? On the Evolution of Aggregative Multicellularity

“…Chimeric load can be observed even when all genotypes are equally proficient at development in monoculture. For example, chimeric M. xanthus fruiting bodies contain fewer spores when the mixed strains originated from different natural fruiting bodies (Mendes-Soares et al 2014;Pande and Velicer 2018). Similarly, chimeric D. discoideum slugs migrate slower than clonal slugs of the same size (Foster et al 2002).…”