A metagenomics approach to investigate microbiome sociobiology

The theory of kin selection is the framework to explain the evolution of social interactions that abound across the diversity of life (1). Observing cooperative behavior posed a challenge to Darwin, but with social insects in mind he proposed that natural selection at the family level can favor helping relatives reproduce (2). His ideas, and the work of Price, built the foundation for Hamilton’s rule, stating that the cost of helping others, in terms of lost reproductive output, may be offset if help is directed toward increasing reproduction of sufficiently close relatives. As such, the investment in passing on genes through relatives contributes to the inclusive fitness of an organism (3). The stark division of labor in some social insects, between sterile workers and reproductive royals, in particular begged an explanation that kin selection provided. Moreover, kin selection has since also helped to explain cooperative behaviors in mammals, birds, algae, and microbes (4). Estimating and analyzing inclusive fitness effects of social traits and applying concepts from kin selection requires the estimation of relatedness between actors and recipients—a challenge in complex microbial communities. In PNAS, Simonet and McNally (5) propose an approach based on the analysis of metagenomes in fecal microbiomes from healthy donors. Their work opens a frontier for kin selection theory by exploring the associations between relatedness and cooperative trait distributions in human gut bacteria. The field of sociomicrobiology has taken off over the last 20 years (6, 7). In microbes, short generation times, tools for their genetic manipulation, and small space requirements have opened a plethora of opportunities to test central tenets of social evolution theory, under controlled conditions that were unattainable using, for example, beehives or ant colonies. With often simple experimental designs it has been shown that production of secreted public goods, such as siderophores … [↵][1]1To whom correspondence may be addressed. Email: sbandersen{at}sund.ku.dk. [1]: #xref-corresp-1-1