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Reduced injury risk links sociality to survival in a group-living primate - PubMed

  • ️Sat Jan 01 2022

Reduced injury risk links sociality to survival in a group-living primate

Melissa A Pavez-Fox et al. iScience. 2022.

Abstract

Sociality has been linked to a longer lifespan in many mammals, including humans. Yet, how sociality results in survival benefits remains unclear. Using 10 years of data and over 1,000 recorded injuries in rhesus macaques (Macaca mulatta), we tested two injury-related mechanisms by which social status and affiliative partners might influence survival. Injuries increased individual risk of death by 3-fold in this dataset. We found that sociality can affect individuals' survival by reducing their risk of injury but had no effect on the probability of injured individuals dying. Both males and females of high social status (measured as female matrilineal rank and male group tenure) and females with more affiliative partners (estimated using the number of female relatives) experienced fewer injuries and thus were less likely to die. Collectively, our results offer rare insights into one mechanism that can mediate the well-known benefits of sociality on an individual's fitness.

Keywords: Biological Sciences; animal behavior; zoology.

© 2022 The Authors.

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Conflict of interest statement

The authors declare no competing interests.

Figures

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Graphical abstract
Figure 1
Figure 1

Injury-related mechanisms by which components of sociality (social status, affiliative partners) can influence survival A direct effect of sociality on survival (gray arrow) has been well established in mammals,,,,, including studies in the Cayo Santiago population,. We explore mechanisms related to injury by which the relationship between sociality and survival might come about. According to the first mechanism, sociality influences the risk of injury (yellow arrow) and, therefore, survival (red arrow). According to the second mechanism (green arrow), sociality affects the survival trajectories of injured individuals.

Figure 2
Figure 2

Effect of injuries on survival (A) Survival curves adjusted for covariates for injured and uninjured individuals. Injured individuals (red solid line, n = 571, 294 females, 277 males) had a near 3-fold increase in the probability of dying compared to uninjured animals (gray dashed line, n = 1030, 557 females, 473 males) (Hz = 1.07 ± 0.17, z = 6.24, p < 0.01, injuries (i) = 1041, deaths (d) = 443). Curves represent males during the mating season, but those for females were similar. Shaded areas represent standard errors. (B) Hazard ratios of death for females and males as a function of the severity of injuries. The main cause of injury-related death was from severe injuries in males (green circles, n uninjured = 473, n non-severely injured = 189, n severely injured = 251), and non-severe injuries in females (Pink squares, n uninjured = 557, n non-severely injured = 232, n severely injured = 147) (Hz severity∗sexM = 1.49 ± 0.72, z = 2.06, p = 0.039, i = 398, d = 107). Uninjured females represent the intercept and vertical bars depict the 95% confidence interval. Statistical significance in a post-hoc analysis is indicated by asterisks where ∗∗p < 0.01. All other pair-wise comparisons within and between sexes were not significant.

Figure 3
Figure 3

Effect of social status on injury risk (A) Injury risk for females as a function of matrilineal rank and age. Females from lower-ranking matrilines (yellow dashed line, n = 510, 237 injuries) had higher chances of being injured than females from higher-ranking matrilines (purple solid line, n = 325, 211 injuries), with increasing probabilities for older females (odds rankLow∗age = 0.23 ± 0.1, z = 2.43, p < 0.01). (B) Injury risk for males as a function of tenure length and age. For visualization, tenure length was categorized by selecting the 20th (273 days of tenure) and 80th (2029 days of tenure) percentiles depicting low status (yellow dashed line) and high status (purple solid line), respectively (n = 748, 536 injuries). Younger males from low status (shorter tenure) had higher injury risk than high-status (longer tenure) young males, yet the opposite occurred at later ages (odds tenure∗age = 0.1 ± 0.03, z = 3.04, p < 0.01). In both plots, shaded areas represent standard errors and gray dots the raw data used in the models (top: injured, bottom: uninjured).

Figure 4
Figure 4

Effect of affiliative partners on injury risk The x-axis represents the number of adult female relatives (extended family, r ≥ 0.125) present in a female’s group (n = 851, injuries (i) = 491). Females with more relatives had lower chances of suffering from an injury than females with fewer relatives (odds = −0.13 ± 0.05, z = −2.5, p = 0.01, i = 491). Shaded areas represent standard errors, and gray dots the raw data used in the models (top: injured, bottom: uninjured).

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