The consequence of inbreeding for modulating social relationships between competitors

Abstract

Extreme inbreeding is likely severely to compromise an animal’s ability to discriminate between individuals that are genetically very similar or identical, and thus to assess their familiarity and kinship with conspecifics. We tested whether male laboratory mice of the outbred ICR strain and the inbred BALB/c strain could discriminate between familiar companions and unfamiliar males of their own strain, or between unfamiliar mice from their own or the other strain, by examining both responses to the males’ scents and competitive aggression during direct interactions. Outbred ICR males spent more time investigating odours of unfamiliar males and were more aggressive towards unfamiliar males than towards familiar companions of their own strain. BALB/c males failed to discriminate between familiar and unfamiliar males of their own strain, showing little aggression to both. In contrast, most BALB/c males (17/24) were aggressive towards unfamiliar ICR males and investigated their scent for longer than that from their own strain. The low level of aggression towards unfamiliar own-strain males suggests that the inbred males failed to recognise that unfamiliar individuals were not their familiar cagemates. They were unable to discriminate between different individuals from their own strain using either chemical or other additional cues of individual identity available during direct interaction.