AbstractAmong animals’ societies, dominance is an important social factor that influences inter-individual relationships. However, assessing dominance hierarchy can be a time-consuming activity which is potentially impeded by environmental factors, difficulties in the recognition of animals, or through the disturbance of animals during data collection. Here we took advantage of novel devices, Machines for Automated Learning and Testing (MALT), designed primarily to study nonhuman primates’ cognition - to additionally measure the social structure of a primate group. When working on a MALT, an animal can be replaced by another; which could reflect an asymmetric dominance relationship (or could happen by chance). To assess the reliability of our automated method, we analysed a sample of the automated conflicts with video scoring and found that 75% of these replacements include genuine forms of social displacements. We thus first designed a data filtering procedure to exclude events that should not be taken into account when automatically assessing social hierarchies in monkeys. Then, we analysed months of daily use of MALT by 25 semi-free ranging Tonkean macaques (Macaca tonkeana) and found that dominance relationships inferred from these interactions strongly correlate with the ones derived from observations of spontaneous agonistic interactions collected during the same time period. We demonstrate that this method can be used to assess the evolution of individual social status, as well as group-wide hierarchical stability longitudinally with minimal research labour. Further, it facilitates a continuous assessment of dominance hierarchies, even during unpredictable environmental or challenging social events. Altogether, this study supports the use of MALT as a reliable tool to automatically and dynamically assess social status within groups of nonhuman primates, including juveniles.
Sperm competition within a dominance hierarchy: investment in social status vs. investment in ejaculates
