More social species live longer

What are the benefits and costs of sociality? Social organisms may enjoy benefits such as sharing resources, being better protected from predators, and having support to raise offspring. However, by living in more tightly packed groups, social organisms may also suffer disadvantages such as the spread of disease, increased competition, aggression, and conflict.

A new study led by the University of Oxford has carried out a comprehensive assessment on the link between sociality and different life history traits such as generation time, life expectancy, and the length of their reproductive window. Up to now, research evaluating the overall impacts of sociality on performance has focused on single species or groups, such as birds or some mammals. The new study assessed 152 animal species from a wide variety of taxonomic groups, including birds, mammals, insects, and corals.

The results of the study showed that more social species live longer, postpone maturity, and are more likely to reproduce successfully than more solitary species. While social species may not be the best to adapt and benefit from a rapidly changing environment, they are often more resilient as a group. This novel finding supports the hypotheses that, even though sociality comes with some obvious costs, the overall benefits are greater.

The study also revealed that sociality does influence the reduction in an animal's ability to reproduce or survive as they age, known as senescence. For example, social allies may help protect against predation, increasing lifespan, but the stress of social hierarchies and conflicts can have the opposite effect.

Lead author Associate Professor Rob Salguero-Gómez (Department of Biology, University of Oxford) said: "Sociality is a fundamental aspect of many animals. However, we still lack cross-taxonomic evidence of the fitness costs and benefits of being social. Here, by using an unprecedented number of animal species this work has demonstrated that species that are more social (most monkeys, humans, elephants, flamingos, and parrots) display longer life spans and reproductive windows than more solitary species (some fish, reptiles, and some insects)."

Whereas previous studies have tended to class sociality as a binary category (i.e. a species is either not social, or social), this new study recognised that sociality exists as a spectrum across animal species.* The continuum used included more 'intermediate' ways of sociality, such as being gregarious (e.g., wildebeests, zebras, flock-forming birds), communal (e.g., purple martin birds), or colonial (e.g., nesting birds, some wasps, coral polyps). The data were accessed via the open access COMADRE Animal Matrix Database (www.compadre-db.org), which is curated by his Associate Professor Salguero-Gómez's research group at the University of Oxford.

Associate Professor Salguero-Gómez added: "In a post-COVID era, where the impacts of isolation have been quite tangible to humans (a highly social species), the research demonstrates that, across a comparative lens, being more social is associated with some tangible benefits."

Further research is ongoing in Associate Professor Salguero-Gómez's research group to expand the database and combine the data with lab work and further modelling to estimate how more social populations buffer (or fail to) against climate change.

*Sociality was classified following the proposed continuum which shows that sociality is not binary:

• solitary: individuals spend their time alone, except to breed e.g. tigers
• gregarious: individuals spend time in groups but social interactions are loose e.g. wildebeests
• communal: individuals live in close proximity and often share a common nesting or dwelling area, but do not engage in cooperative breeding e.g. purple martin
• colonial: individuals live in close proximity and always share a common nesting or living area e.g. nesting birds
• social: individuals live in close proximity and form stable, organised groups, engaging in social behaviours such as cooperative breeding and hierarchical structures e.g. elephants