Are Baseline Glucocorticoid Levels Linked to Aggressive Behaviour in Wild Wood Mice?

ABSTRACT Defensive strategies of prey species constitute a key element to survive and maximise biological fitness in natural environments. However, some of the mechanisms underlaying antipredator behaviours are not clear. Despite previous studies had attempted to unravel the relationship between aggressiveness and glucocorticoids (GC), this association remains uncertain. Our study aimed to find an explicit link between the aggressive behaviour in the wood mice (Apodemus sylvaticus) and the GC release. For this, a live-trapping study was conducted in the Montes do Invernadeiro Natural Park (NW Spain). We collected faecal samples from 76 captures to measured free-ranging mice baseline faecal corticosterone metabolites (FCM) levels using an enzyme immunoassay. Moreover, we determined the aggressive behaviour of each mice by measuring the number of bites perpetrated upon the researcher while handling. Results of the statistical model showed that aggressive behaviour in mice was not explained by FCM concentrations. On the other hand, a better body condition was associated with the individual's aggressiveness. Moreover, it seems that recaptured individuals tended to be more aggressive, probably because previous experience with this life-threatening event improved the individual's defensive performance in order to successfully escape again.