Decoupling social status and status certainty effects on health in macaques: a network approach

Abstract

Background: Although a wealth of literature points to the importance of social factors on health, a detailed understanding of the complex interplay between social and biological systems is lacking. Social status is one aspect of social life that is made up of multiple structural (humans: income, education; animals: mating system, dominance rank) and relational components (perceived social status, dominance interactions). In a nonhuman primate model we use novel network techniques to decouple two components of social status, dominance rank (a commonly used measure of social status in animal models) and dominance certainty (the relative certainty vs. ambiguity of an individual's status), allowing for a more complex examination of how social status impacts health.

Methods: Behavioral observations were conducted on three outdoor captive groups of rhesus macaques (N = 252 subjects). Subjects' general physical health (diarrhea) was assessed twice weekly, and blood was drawn once to assess biomarkers of inflammation (interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and C-reactive protein (CRP)).

Results: Dominance rank alone did not fully account for the complex way that social status exerted its effect on health. Instead, dominance certainty modified the impact of rank on biomarkers of inflammation. Specifically, high-ranked animals with more ambiguous status relationships had higher levels of inflammation than low-ranked animals, whereas little effect of rank was seen for animals with more certain status relationships. The impact of status on physical health was more straightforward: individuals with more ambiguous status relationships had more frequent diarrhea; there was marginal evidence that high-ranked animals had less frequent diarrhea.

Discussion: Social status has a complex and multi-faceted impact on individual health. Our work suggests an important role of uncertainty in one's social status in status-health research. This work also suggests that in order to fully explore the mechanisms for how social life influences health, more complex metrics of social systems and their dynamics are needed.

Keywords: Dominance certainty; Inflammation; Nonhuman primate; Social network analysis; Status.

Figure 1. Inference of dominance rank and certainty using a network.

(A) Although animals A and D do not directly interact, it can be inferred that A outranks D through the indirect pathways in the network. Certainty for this inference is increased when multiple pathways flow in the same direction (i.e. from A to D). (B) Although animals F and I do not interact, it can be inferred through the most direct pathway (through individual J) that I outranks F. Certainty for this inference, however, is lower due to the contradictory flow of dominance from F to I (through individuals G and H).

Figure 2. Rank and dominance certainty.

Scatter plot of dominance rank and dominance certainty. Markers indicate group membership.

Figure 3. Sex differences in the impact of dominance certainty and rank on CRP.

Predicted values of CRP. Panels A and B depict effects for CRP for males and females, respectively (based on model H8). Separate lines represent the interaction between dominance rank and dominance certainty.

Figure 4. The impact of dominance certainty and rank on inflammation based on serum levels of interleukin-6 (IL-6).

Predicted values of IL-6 based on model H5. Separate lines represent the interaction between dominance rank and dominance certainty.

Figure 5. Sex differences in the impact of dominance certainty and rank on inflammation based on serum levels of interleukin-6 (IL-6).

Predicted values of IL-6 based on model H8. Panels A and B depict effects for IL-6 for males and females, respectively. Separate lines represent the interaction between dominance rank and dominance certainty.

Figure 6. Dominance certainty moderates the effect of rank on TNF-α.

Predicted values for TNF-α based on model H5. Separate lines represent the interaction between rank and dominance certainty.