Effects of intergroup competition on the behaviour and reproductive success of female house mice

Explaining variation in cooperative and competitive behaviour is a fundamental challenge in behavioural ecology. In group-living animals, there is growing interest in the influence of intergroup competition on cooperative behaviour. For mammals, this research focus shifts emphasis to competitive interactions between females, which have previously received relatively little attention. In this study, I use the house mouse (Mus musculus domesticus) as a model species that exhibits a flexible social system with cooperative breeding, to test the effects of intergroup competition on female intragroup cooperation and investment in competition throughout a breeding cycle. I conduct a large-scale longitudinal experiment under controlled naturalistic conditions, using a multifaceted approach to collect data on individual behaviours, physiologies (major urinary proteins, oxytocin, and corticosterone) and reproductive success, as well as data on group level competitive signalling. From offspring born in this experiment I also test how intergroup competition can impact future behaviours relevant to social stress. Overall, my research shows that females invest in competitive signalling and increase their investment in response to mate availability and the presence of competitors, but I found no evidence for a trade-off between investment in competitive signalling and reproductive success. I also found no evidence that intergroup competition leads to greater cooperation between female house mice, but my findings instead support an alternative hypothesis of induced tension linked to the presence of competitors. Intergroup competition experienced by mothers had no influence on offspring behaviours at maturity, but the behaviours tested did form personality traits and behavioural syndromes, potentially linked to genotypes or early life environmental factors not tested here. I conclude that species with diverse social systems should be studied to fully understand the consequences of intergroup competition for female behaviour and reproductive success