Focused grooming networks and stress alleviation in wild female baboons

Abstract

We examine the relationship between glucocorticoid (GC) levels and grooming behavior in wild female baboons during a period of instability in the alpha male rank position. All females' GC levels rose significantly at the onset of the unstable period, though levels in females who were at lower risk of infanticide began to decrease sooner in the following weeks. Three factors suggest that females relied on a focused grooming network as a coping mechanism to alleviate stress. First, all females' grooming networks became less diverse in the weeks following the initial upheaval. Second, females whose grooming had already focused on a few predictable partners showed a less dramatic rise in GC levels than females whose grooming network had been more diverse. Third, females who contracted their grooming network the most experienced a greater decrease in GC levels in the following week. We conclude that close bonds with a few preferred partners allow female baboons to alleviate the stress associated with social instability.

Figure 1

Weekly glucocorticoid (GC) levels of all adult females between 23 May and 3 July 2007. FT re-immigrated on 31 May and SO disappeared on 4 June (both week 0), starting the male rank instability. All females have been lumped together. Thick lines show averages, boxes represent 50% and whiskers show SD.

Figure 2

Grooming diversity (SWDI) of lower risk and higher risk females during week −1 (white bars: before immigration event) and week 1 (grey bars: after immigration event). Legend as in Fig. 1.

Figure 3

Correlation between cycling and pregnant females’ grooming diversity (SWDI) before the male rank upheaval and their increase in glucocorticoid (GC) levels in the following week (increase = GC_week1 − GC_week-1). One outlier was removed.

Figure 4

Regression between females’ dominance rank and the change in their glucocorticoid (GC) levels: (a) lower risk females’ change in GC levels between weeks 1 and 2 (change index = GC_week2 − GC_week1) and (b) higher risk females’ change in GC levels between week 2 and 3 (change index = GC_week3 − GC_week2).

Figure 4

Regression between females’ dominance rank and the change in their glucocorticoid (GC) levels: (a) lower risk females’ change in GC levels between weeks 1 and 2 (change index = GC_week2 − GC_week1) and (b) higher risk females’ change in GC levels between week 2 and 3 (change index = GC_week3 − GC_week2).