Behavioural and physiological consequences of home advantage resource holding in male guinea pigs

Abstract

This study tested the physiological and behavioural effects of a resource asymmetry between guinea pig males. Asymmetry was defined via cohabitation with a female in a home area during a 5-day period. An experimental setup was designed in which the same male alternated between being in this home area (and monopolizing a female therein) and playing the role of an intruder. The confrontation phase between the resource holder and the intruder lasted 5 days. Behavioural data were collected for 0.5 h at the start of the confrontation and again for 0.5 h at 3, 24, 72, and 120 h after the onset of confrontation. Blood samples were taken before the test started and after 3, 72, and 120 h. Body mass was registered before and after the confrontation phase. The results indicate that resource holders were more highly motivated than intruders in displaying aggressiveness. They exhibited more chasing behaviour and won more confrontations. Both male groups performed almost identical frequencies of threat displays and courtship behaviour. Physiologically, the resource holders lost less body mass and showed increased plasma testosterone concentrations after 120 h. Resource holders also exhibited steady plasma corticosteroid concentrations, whereas the intruders showed elevated corticosteroid levels at 72 and 120 h. The results show that when acting as a resource holder, males react according to the resident-always-wins hypothesis, and when acting as an intruder, lose most confrontations. We conclude that the behavioural and physiological reaction of males during confrontations is determined to a greater extent by environmental asymmetries than by experiences or physical conditions before the conflict.