Biology subjects

Siracusa, E. R.

Publications and source records attributed to Siracusa, E. R..

4 recordsLinked to original sources

bioRxiv2022

Ageing in a collective: The impact of ageing individuals on social network structure

Ageing affects many phenotypic traits, but its consequences for social behaviour have only recently become apparent. Social networks emerge from associations between individuals. The changes in sociality that occur as individuals get older are thus likely to impact network structure, yet this remains unstudied. Here we use empirical data from free-ranging rhesus macaques and an agent-based model to test how age-based changes in social behaviour feed up to influence: (1) an individuals level of indirect connectedness in their network; and (2) overall patterns of network structure. Our empirical analyses revealed that female macaques became less indirectly connected as they aged for some, but not all network measures examined, suggesting that indirect connectivity is affected by ageing, and that ageing animals can remain well integrated in some social contexts. Surprisingly, we did not find evidence for a relationship between age distribution and the structure of female macaque networks. We used an agent-based model to gain further understanding of the link between age-based differences in sociality and global network structure, and under which circumstances global effects may be detectable. Overall, our results suggest a potentially important and underappreciated role of age in the structure and function of animal collectives, which warrants further investigation.

animal behavior and cognition↗

bioRxiv2022

Within-individual changes reveal increasing social selectivity with age in rhesus macaques

Accumulating evidence in humans and other mammals suggests older individuals tend to have smaller social networks. Uncovering the cause of these declines is important as it can inform how changes in social relationships with age might affect health and fitness in later life. Smaller social networks might be detrimental, but may also be the result of greater selectivity in partner choice, reflecting an adaptive solution to physical or physiological limitations imposed by age. While greater selectivity with age has been shown in humans, the extent to which active social selectivity within an individuals lifetime occurs across the animal kingdom remains an open question. Using 8 years of longitudinal data from a population of free-ranging rhesus macaques we provide the first evidence in a non-human animal for within-individual increases in social selectivity with age. Going beyond previous cross-sectional studies, our within-individual analyses revealed that adult female macaques actively reduced the size of their networks as they aged and focused on partners previously linked to fitness benefits, including kin and partners to whom they were strongly and consistently connected earlier in life. Females spent similar amounts of time socializing as they aged, suggesting that network shrinkage does not result from lack of motivation or ability to engage. Furthermore, females remained attractive companions and were not isolated by withdrawal of social partners. Taken together, our results provide rare empirical evidence for social selectivity in non-humans, suggesting patterns of social aging in humans may be deeply rooted in primate evolution and may have adaptive value. Significance statementThe narrowing of social networks and prioritization of meaningful relationships with age is commonly observed in humans. Determining whether social selectivity is exhibited by other animals remains critical to furthering our understanding of the evolution of late-life changes in sociality. Here we test key predictions from the social selectivity hypothesis and demonstrate that female rhesus macaques show within-individual changes in sociality with age that resemble the human social aging phenotype. Our use of longitudinal data to track how individuals change their social behavior within their lifetimes offers the most conclusive evidence to date that social selectivity is not a phenomenon unique to humans and therefore might have deeper evolutionary underpinnings.

animal behavior and cognition↗

bioRxiv2022

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

Affiliative social relationships and high social status predict longer lifespans in many mammal species, including humans. Yet, the mechanisms by which these components of sociality influence survival are still largely unknown. Using 10 years of data and over 1000 recorded injuries from a free-ranging population of rhesus macaques (Macaca mulatta), we investigated two possible mechanisms that could underpin the relationship between sociality and survival: sociality (1) reduces injury risk; and/or (2) increases the probability of survival after an injury. We found that sociality can affect an individuals survival by influencing their risk of injury, but had no effect on the probability of injured individuals dying. Individuals with more affiliative partners experienced fewer injuries compared to less socially integrated. Social status was also associated with lower risk of injury, particularly for older high-ranking individuals. These results represent the first demonstration of a link between social integration and fatal injury risk in a group-living species, and are the first to link social status, injury risk and survival outside of humans. Collectively, our results offer insights into a mechanism that can mediate the well-known benefits of sociality on an individuals fitness.

evolutionary biology↗

bioRxiv2021

Sociodemographic effects on immune cell composition in a free-ranging non-human primate.

Increasing age is associated with dysregulated immune function and increased inflammation- patterns that are also observed in individuals exposed to chronic social adversity. Yet we still know little about how social adversity impacts the immune system and how it might promote age-related diseases. Here, we investigated how immune cell diversity varied with age, sex and social adversity (operationalized as low social status) in free-ranging rhesus macaques. We found age-related signatures of immunosenescence, including lower proportions of CD20+ B cells, CD20+/CD3+ ratio, and CD4+/CD8+ T cell ratio - all signs of diminished antibody production. Age was associated with higher proportions of CD3+/CD8+ Cytotoxic T cells, CD16+/CD3-Natural Killer cells, CD3+/CD4+/CD25+ and CD3+/CD8+/CD25+ T regulatory cells, and CD14+/CD16+/HLA-DR+ intermediate monocytes, and lower levels of CD14+/CD16-/HLA-DR+ classical monocytes, indicating greater amounts of inflammation and immune dysregulation. We also found an effect of exposure to social adversity (i.e., low social status) that was sex-dependent. High-status males, relative to females, had higher CD20+/CD3+ ratios and CD16+/CD3 Natural Killer cell proportions, and lower proportions of CD8+ Cytotoxic T cells. Further, low status females had higher proportions of cytotoxic T cells than high status females, while the opposite was observed in males. High status males had higher CD20+/CD3+ ratios than low status males. Together, our study identifies immune cell types that differ by age in a human-relevant primate model animal, and demonstrates a novel link between sex-dependent immunity and social adversity.

immunology↗