Does inbreeding affect personality traits? An experimental study in a precocial bird

Inbreeding is known to have deleterious effects on offspring performance, but the extent to which such inbreeding depression acts on traits is widely variable. In particular, condition-dependent traits that are subject to directional selection are expected to show stronger inbreeding depression. However, while inbreeding effects on primary determinants of fitness have been thoroughly investigated, the impact of inbreeding on other potentially condition-dependent traits such as behavioural and “personality” traits remain little studied. Here, we performed experimental matings between full-siblings and unrelated individuals of Japanese quail (Coturnix japonica) and tested the effect of inbreeding on eight behavioural traits hypothesized to be linked to “personality” differences. Structural equation modelling revealed that these traits were part of a behavioural syndrome involving two a priori hypothesised latent variables, described as emotivity and neophobia. These were underlying all the measured behavioural traits and covaried negatively. Yet, we found no behavioural differences between inbred and outbred offspring, except for tonic immobility, which was longer in inbred offspring. We therefore conclude that inbreeding only has limited effects on behavioural traits linked to personality, suggesting that variation in these behaviours is not underlain by rare recessive deleterious alleles, as predicted when a trait is not condition dependent.