I’m going to keep this weeks post short - grant and code writing are hanging over my head as I type this.

The seminar this week was given by Elizabeth Archie from the University of Notre Dame. Her talk title was Social relationships health and fitness in wild baboons the portion of her research that she shared with us today focused on how social behavior contributes to health. Her work in this area has focused on baboons. She studies two social groups in Amboseli national park in Kenya. These groups have many similarities to humans for instance they are terrestrial and contain multiple male and female adults.

There are some aspect of social behavior that have very obvious consequences for health. For instance we know that social lifestyles can lead to greater risk of harmful infections. However, we understand less about the possible positive effects. Do social interactions contribute to differences in the gut microbiome? Do these changes have positive or negative net affect on health and longevity?

A first step in understanding this might be to try and understand what determines the character of the gut microbiome. We know that social partners have more similar gut microbiomes than nonsocial partners but we don’t know exactly why. Social partners often share diets, genetic ancestry, and habitat are any of these key in determining the microbiome?

Archie’s group has begun to unravel this through an ambitious project using metagenome shotgun sequencing of fecal samples. They sampled 48 adults from two groups over a one month period. The two groups were adjacent and each had a range of around 12.5 square miles during this month. This is an awesome dataset that allows lots of really interesting questions to be asked:

1. Does social group explain differences in microbiome?
2. Do social networks within groups explain differences in microbiome?
3. Are all microbe groups equally influenced by social behavior?

So to test this first question we can look at a simple PCA and ask if differences in the taxonomic groups or genes present in the shotgun samples are able to differentiate the two groups. Indeed we see that the PCA shows that we can easily separate these two groups. Social group membership explains about 18% of difference in the taxonomic makeup of the gut microbiome, and about 10% of the differences in the genes present in the gut microbiome. I was curious about this difference 18% to 10% does this have important implications? To me this suggests that regardless of the species mix we have in our gut microbiome we converge on a community that is adapted to accomplish similar metabolic goals. Not sure exactly what the appropriate test for that would be, and this is probably already well established (not my subfield).

this is a screen shot of a figure from the 2015 elife paper on the left we have PCA based on taxonomy included in the sequences on the right based on KEGG enzyme orthology (type of genes). Mica and Viola  are the names for the two social groups being studied.

Now for question two. Do differences in within group social behavior have predictable contributions to gut microbiome content? This is where the nature of this dataset gets cool. It ends up that these 48 baboons that were sequenced have also been observed and their social interactions have been extensively documented. This results in pairwise measures of social connection between all individuals in a population. They have great looking figures of this (I’m not sure how much quantitative information an average user extracts from these - could the position of the figures be optimized to minimize crossing lines? - perhaps they are?).

This is a screen shot of a figure from the 2015 elife paper. The thickness of the line indicates the strength of social connection between individuals.  Social connections are measured based on grooming between pairs - Elizabeth tells us that this is a good measure of social connection since it is the primary activity used to build and maintain friendships in these baboons.

What we see (in both social groups) is that the strength of social interaction between two individuals is corelated with the similarity of their gut microbiomes.
 
Now for that final question, is it certain microbes that are producing this signal. We could easily imagine that many microbes are ubiquitous and widely available from the environment. Perhaps it is only a subset (fragile ones that don’t last long in the “wild”) that we see social behavior as the determining factor in their presence or absence. The approach that Archie’s group took was to see if the same taxonomic groups show enrichement between the two main groups and within the social network of one group. They found that indeed there is a subset of taxonomic groups that do seem to be prone to the effects of social behavior. To take this a step further the authors turned to the Genomes Online Database to ask if the identified groups were prone to be non spore forming species that might not persist outside of a host. This is indeed what the authors found the identified groups were “consistently enriched (relative to all species or genera tested) for an anaerobic, non-spore forming lifestyle”


This one only the first half of Beth’s talk she also shared fascinating work that her group has done looking at the effect of early life hardship on longevity. You can find links to this and some of the groups other fascinating work below.


The Archie Lab

Elizabeth A. Archie Google Scholar Profile

Manuscripts resulting from the projects mentioned above:

Social networks predict gut microbiome composition in wild baboons.

Social affiliation matters: both same-sex and opposite-sex relationships predict survival in wild female baboons.