Aggregation, status competition and levelling mechanisms in prehistoric Chulmun, Korea

This article discusses the aggregation and dispersion of the Chulmun hunter-gatherers (c. 8000–1500 bce) in prehistoric Korea. The following observations are made from settlement datasets. First, large numbers of houses do not necessarily imply aggregation, as they can be palimpsests of dwelling structures from different phases. Second, aggregation settlements were segmented and contained multiple discrete subunits. Individual residential clusters typically had fewer than 60 inhabitants. Third, there are some indications of social hierarchy in nucleated settlements such as Unseo-dong. Fourth, despite some evidence of emergent elites and social differentiation, social complexity did not intensify over the long run. Levelling mechanisms (e.g. group fission) were in operation and they suppressed the institutionalization of social hierarchy.

Collective decision-making appears more egalitarian in populations where group fission costs are higher

Collective decision-making is predicted to be more egalitarian in conditions where the costs of group fission are higher. Here, we ask whether Trinidadian guppies ( Poecilia reticulata ) living in high or low predation environments, and thereby facing differential group fission costs, make collective decisions in line with this prediction. Using a classic decision-making scenario, we found that fish from high predation environments switched their positions within groups more frequently than fish from low predation environments. Because the relative positions individuals adopt in moving groups can influence their contribution towards group decisions, increased positional switching appears to support the prediction of more evenly distributed decision-making in populations where group fission costs are higher. In an agent-based model, we further identified that more frequent, asynchronous updating of individuals' positions could explain increased positional switching, as was observed in fish from high predation environments. Our results are consistent with theoretical predictions about the structure of collective decision-making and the adaptability of social decision-rules in the face of different environmental contexts.

Divergence in gut microbial communities mirrors a social group fission event in a black-and-white colobus monkey (Colobus vellerosus)

ABSTRACTHost behavior and social factors have increasingly been implicated in structuring the composition of gut microbial communities. In social animals, distinct microbial communities characterize different social groups across a variety of taxa, although little longitudinal research has been conducted that demonstrates how this divergence occurs. Our study addresses this question by characterizing the gut microbial composition of an African Old World monkey, the black-and-white colobus (Colobus vellerosus), prior to and after a social group fission event. Gut microbial taxonomic composition of these monkeys was profiled using the V-4 hypervariable region of the bacterial 16s rRNA gene, and pairwise-relatedness values were calculated for all individuals using 17 STR loci and partial pedigree information. The two social groups in this study were found to harbor distinct microbial signatures after the fission event from which they emerged, while these communities were not divergent in the same individuals prior to this event. Three genera were found to differ in abundance between the two new social groups: Parabacteroides, Coprococcus, and Porphyromonadaceae. Additionally, although this fission happened partially along lines of relatedness, relatedness did not structure the differences that we found. Taken together, this study suggests that distinct gut microbial profiles can emerge in social groups in less than one year and recommends further work into more finely mapping the timescales, causes, and potentially adaptive effects of this recurring trend toward distinct group microbial signatures.Research highlightsDistinct gut microbial profiles emerge in two social groups of C. vellerosus less than nine months after a fission event.Three genera differ in abundance between the two new social groups.Relatedness does not structure differences in microbial composition between the groups.