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 behavior is the first response to changing conditions. Behavioral flexibility can potentially improve an organism's chances to survive and reproduce. Currently, we lack an understanding on the time-scale such behavioral adjustments need, how they actually affect reproduction and survival and whether behavioral 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, that is, adjustments only becoming visible in the offspring generation. Mice lived in 6 experimental populations of semi-natural environments either on high or standard quality food for 4 generations. We showed previously that high-quality food induced better conditions 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 with 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 toward environmental change, thus, highlighting the importance of the environment and the mode of response for evolutionary models.