Generating synthetic multi-national longitudinal cohorts for clinically grounded HIV research.

Intergroup conflict is a potent evolutionary force that has shaped social structure, territoriality and cooperation from ants to apes, including in humans. Contests between conspecific groups have been well-studied in diverse taxa, highlighting a range of immediate and delayed fitness consequences. Antagonistic interactions with outsiders, especially those involving physical attacks, can lead to loss of life or breeding position, while there can also be knock-on consequences from contest-induced injuries and takeovers, including changes in behaviour and space use. The costly nature of intergroup contests means that, much as information about predator occurrence in the environment generates a ‘landscape of fear’ for prey to navigate, the presence of conspecific rivals creates a ‘landscape of conflict’. In line with the way that prey pre-emptively alter their behaviour in relation to the ecological pressure of the predation landscape (that is, use experience and current information to optimize behaviour ahead of a potential future interaction), animal groups should benefit by responding to the variation in threat posed by rival groups. Humans respond to the threat of intergroup contests by increasing their surveillance for rivals when in conflict zones and moving quietly through enemy territory to avoid detection. There are also a few examples of similar location-related behaviour in non-human animals. For instance, recent work showed that two chimpanzee () groups used elevated vantage points when moving towards territorial borders, while raiding parties of males go silent when entering another territory. However, research has been largely primate focused, and the evidence is equivocal: there is inconsistency between species in how space use and behaviour relates to the increase in intergroup risk that is predicted towards territory borders. One reason is that the location-based risk of encountering other groups often correlates with environmental variables, such as food availability or habitat type, generating edge effects that can mask the threat attributable to intergroup rivals. Moreover, there is large variation in the threat posed by different rival groups; this key factor is currently unexplored in a pre-emptive context. In contrast to predators, where each individual of a given species provides a relatively comparable threat, conspecific groups can vary hugely in their competitive ability, with the intensity and outcome of intergroup contests known to depend on the characteristics of the rivals. Arguably the most important single factor is group size, which relates positively to resource-holding potential in many social species. As larger groups are usually at an advantage in contests, engaging with them carries greater risks, including potential mortality; in many cases, early detection and retreat will be the best strategy for relatively smaller groups. However, well-matched competitors (for example, those with similar group sizes) often participate in more prolonged, escalated contests, which incur greater costs in terms of time, energy and injury risk; preparing for such encounters may give groups an important advantage and be just as important as preparing for much large rivals. However, it is unknown in what ways the relative group size of rivals influences the pre-emptive decisions of non-human animals and how they integrate variable threat levels into their ecological landscape of conflict.