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

Abstract

Social integration and support can have profound effects on human survival. The extent of this phenomenon in non-human animals is largely unknown, but such knowledge is important to understanding the evolution of both lifespan and sociality. Here, we report evidence that levels of affiliative social behaviour (i.e. 'social connectedness') with both same-sex and opposite-sex conspecifics predict adult survival in wild female baboons. In the Amboseli ecosystem in Kenya, adult female baboons that were socially connected to either adult males or adult females lived longer than females who were socially isolated from both sexes--females with strong connectedness to individuals of both sexes lived the longest. Female social connectedness to males was predicted by high dominance rank, indicating that males are a limited resource for females, and females compete for access to male social partners. To date, only a handful of animal studies have found that social relationships may affect survival. This study extends those findings by examining relationships to both sexes in by far the largest dataset yet examined for any animal. Our results support the idea that social effects on survival are evolutionarily conserved in social mammals.

Keywords: intrasexual competition; longevity; social connectedness; social relationships; survival.

Figure 1.

Survival probability for adult female baboons as a function of social connectedness. Plots (a) and (b) depict the effects of SCI-F and SCI-M, respectively; plot (c) depicts the combined effects of female social connectedness to adult females and males. Solid red lines indicate females at the lower 25th percentile for social connectedness, green dotted lines indicate females at the median for social connectedness and blue dashed lines indicate females at the upper 75th percentile for social connectedness. (Online version in colour.)

Figure 2.

Median adult female survival time as a function of social connectedness to (a) adult females and (b) adult males. Large dots indicate the median values of social connectedness; small, flanking dots indicate the top 75th and lower 25th percentiles of social connectedness. Grey shading indicates 95% CIs. (Online version in colour.)

Figure 3.

Mean lifetime female social connectedness to adult males (SCI-M) as a function of mean lifetime dominance rank for 194 adult female baboons. Black line depicts a log fit to the data. Error bars represent standard errors of the mean.