Overall, the project has been a success, with most of what was planned in Objectives 1, 2 and 4 achieved; there were logistical difficulties with Objective 3, exacerbated by covid restrictions, but still some valuable output.
(1) Behavioural consequences
Experiments with cichlid fish and dwarf mongooses investigated behavioural responses over different timeframes to simulated outgroup threats. Short-term fish experiments examined: contributions to territorial defence, within-group interactions and potential punishment of uncooperative individuals; intra-group variation in responses; and the effect of a conspecific audience on behavioural responses. Longer-term manipulations investigated how outgroup threat affects parental care and interactions between group members. Short-term mongoose experiments examined: individual behaviour, within-group interactions and group decisions in response to conflict; responses to different threat levels; and how there can be delayed responses. A longer-term manipulation investigated how elevated outgroup threat can cause extended and cumulative effects on within-group interactions, group decisions and movement patterns. We also used the long-term dwarf mongoose data to examine how new group members from other groups can lead to behavioural changes.
(2) Hormonal consequences
We encountered difficulties validating the fish hormonal levels in water samples (the non-invasive methodology planned to allow repeated testing of the same individuals), which were exacerbated by covid lockdowns that prevented access to relevant laboratories and collaborator expertise. Attempts to collect sufficient saliva non-invasively from the wild mongooses were also not successful, despite trialling several methods. However, we established methods to extract stress hormones from faecal samples. These are being used to determine how different levels of out-group threat affect cortisol and whether there are differences between individuals of different sex and dominance status. Results will be combined with behavioural responses from some of the experiments (see above), with long-term behavioural data and with life-history and reproductive data to investigate potential underpinning mechanisms for responses to outgroup threats. One additional valuable element of the project was using faecal samples from the mongooses to extract DNA for microsatellite assessment of relatedness among group members.
(3) Reproductive consequences
We ran long-term experiments with the cichlid fish to determine how chronic outgroup threat can affect a range of reproductive parameters, including latency to first breed, clutch number and size, egg parameters, parental care, hatching success, and fry growth, performance and survival. Complementary work is considering the potential mechanisms for the effects found (e.g. maternal effects) and whether there can be changes in cognitive performance in breeding pairs due to the level of outsider threat. We used the long-term dwarf mongoose databases to assess how the rate of intergroup conflict affects reproductive output (number of breeding attempts, success of breeding attempts, pup survival) and whether changes in adult vigilance can drive the unexpected positive relationship found. Further analyses will combine behavioural data (e.g. within-group cooperation, parental-care contributions) with life-history data to explore the long-term consequences of outgroup threat further.
(4) Evolutionary consequences
We have built mathematical models to consider the factors influencing within-group conflict over defence against conspecific outsiders seeking breeding positions, how kin blackmail can be a coercive route to altruism and the importance of stochasticity on the evolution of cooperation. We also developed theoretical models to assess the viability of three hypotheses about drifting behaviour (movement to help between groups) and then collected field empirical data on paper wasps to test the most plausible hypothesis. Further analytical modelling and evolutionary simulations has explored how outgroup conflict influences relative investment in attack and defence. In addition, we have provided reviews or the development of hypotheses concerning, for example, the causes and consequences of variation in the responses of group-living species to territorial intrusions, how interactions with conspecific outsiders can drive cognitive evolution and the fitness consequences of outgroup conflict.
The project has generated 26 published peer-review papers (including in Nature, Nature Ecology and Evolution, Nature Communications, PNAS, eLife, Philosophical Transactions and Proceedings of the Royal Society), with several others submitted or in preparation. The research team have given numerous talks and seminars at conferences, workshops and academic institutions. They have also written popular articles, conducted a number of school visits and ensured that the work from this project has a wide audience on social media.
