Endemic social diversity within natural kin groups of a cooperative bacterium

Abstract

The spatial structure of genetic diversity underlying social variation is a critical determinant of how cooperation and conflict evolve. Here we investigated whether natural social groups of the cooperative soil bacterium Myxococcus xanthus harbor internal genetic and phenotypic variation and thus the potential for social conflict between interacting cells. Ten M. xanthus fruiting bodies isolated from soil were surveyed for variation in multiple social phenotypes and genetic loci, and patterns of diversity within and across fruiting body groups were examined. 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. Our results simultaneously highlight the potential for social conflict within Myxococcus social groups and the possibility of social coevolution among diverse related lineages that are clustered in space and cotransmitted across generations.bacterial population structure | micro-scale variation

Chimaeric load among sympatric social bacteria increases with genotype richness

“…Colonymerger incompatibilities evolve readily in both natural populations [16] and experimental lineages (P. Zee & O. Rendueles-Garcia 2012, unpublished results) and might be selectively favoured in soil habitats due to the barriers to inter-migration among non-kin from divergent groups that they create [52]. The potential for chimaeric load to result from the merging of distinct swarms composed of functionally divergent genotypes would contribute to benefits of colonymerger incompatibilities and favour their reinforcement.…”

“…The potential for chimaeric load to result from the merging of distinct swarms composed of functionally divergent genotypes would contribute to benefits of colonymerger incompatibilities and favour their reinforcement. Such incompatibilities appear to generate a very fine scale of social isolation in natural populations that may lead to longterm divergence among sympatric patches of lineage clusters [16]. In turn, such divergence may increase latent chimaeric load (i.e.…”

“…Bacterial populations are highly diverse and individual species can be represented by dozens of distinct genotypes at local scales [8,[14][15][16][17]. Genetically distinct conspecific cells will co-occur in chimaeric local groups due to mutation and possibly migration, and are likely to interact in ways that affect fitness [9,18,19].…”

Social complementation and growth advantages promote socially defective bacterial isolates

“…Natural diversity in the degree to which cooperative traits are expressed by distinct strains within a common social group has been found or postulated to exist in several microbial species [14][15][16][17]. Examples include variation in quorum-sensing signal production in Pseudomonas aeruginosa [18], bioluminescence in Vibrio fisheri [19], and social swarming [20] and spore production [21] in Myxococcus xanthus.…”

“…Naturally variable traits include developmental competitiveness in mixed groups [11,27,42], social swarming rates [20], rate of development [21], allee effects during development [43] and predation range [40]. Kraemer & Velicer [14] found that even closely related clones isolated from within a single fruiting body often vary markedly in their expression of social phenotypes. Three of 10 fruiting bodies they examined harboured genotypes that swarm significantly slower in pure culture than do other clones from the same fruiting body.…”