Personality development in wild house mice: Evidence for a nutrition-dependent sensitive period early in life

Changing environmental conditions pose serious challenges to organisms, for example, by disrupting access to food. Across species and traits, animals use phenotypic plasticity to rapidly adjust to such changes. Previous work has demonstrated that wild house mice are able to adjust stress coping to changing food quality within just three generations. However, we do not know when during ontogeny changing conditions induce phenotypic adjustments. We tested experimentally when during ontogeny (as fetus, newborn, weanling, or late adolescent) a food switch between standard and high-quality food shapes personality development (stress coping and stress perception) in cage-housed, wild house mice (Mus musculus domesticus). Personality traits were assessed in the Open Field and the Elevated Plus Maze at different time points during ontogeny (weaning, early adolescence, late adolescence, and adulthood). We observed three key findings. First, as mice grow older they tend to use more passive stress-coping strategies, indicating higher risk aversion. This relationship holds irrespective of food quality. However, mice fed with high-quality food show, on average, more active stress coping compared to mice receiving standard-quality food. Second, the fetal life stage might be a sensitive period for stress coping in response to experiencing decreases in nutritional quality. Third, experiencing an increase in nutritional quality may slow the age-related switch towards a passive stress-coping strategy. Our findings contrast previous work observing passive stress coping in mice living in semi-natural enclosures fed with high-quality food. We propose that the social environment of mice living in cages vs mice living in small groups may explain these differences. Our results highlight the need for experiments across the breadth of development comparing captive and semi-free-living animals. Ultimately, such studies will help us understand the complex relationships between development, nutrition, the (social) environment, and personality.