Is the speed of adjusting to environmental change condition dependent? An experiment with house mice (Mus musculus)

Environmental conditions change constantly either by anthropogenic perturbation or naturally across space and time. Often, a change in behaviour is the first response to changing conditions. Behavioural flexibility can potentially improve an organism’s chances to survive and reproduce. Currently, we lack an understanding on the time-scale such behavioural adjustments need, how they actually affect reproduction and survival and whether behavioural adjustments are sufficient in keeping up with changing conditions. We used house mice (Mus musculus) to test whether personality and life-history traits can adjust to an experimentally induced food-switch flexibly in adulthood or by intergenerational plasticity, i.e., adjustments only becoming visible in the offspring generation. Mice lived in six experimental populations of semi-natural environments either on high or standard quality food for four generations. We showed previously that high-quality food induced better condition and a less risk-prone personality. Here, we tested whether the speed and/ or magnitude of adjustment shows condition-dependency and whether adjustments incur fitness effects. Life-history but not personality traits reacted flexibly to a food-switch, primarily by a direct reduction of reproduction and slowed-down growth. Offspring whose parents received a food-switch developed a more active stress-coping personality and gained weight at a slower rate compared to their respective controls. Furthermore, the modulation of most traits was condition-dependent, with animals previously fed with high-quality food showing stronger responses. Our study highlights that life-history and personality traits adjust at different speed towards environmental change, thus, highlighting the importance of the environment and the mode of response for evolutionary models.