Survival under conditions of environmental stress: Variability of brain morphology and behavior in the house mouse

Two populations of laboratory mice lived outdoors in open pens for two year s. Thereafter, some of them were bred in the laboratory. Morphometric analy sis showed that the size of the synaptic projection area of messy fibers (i n the CA3 region of the hippocampus), which has an important functional rol e, and some behavioral traits of the open-pen mouse progeny had significant genetically determined differences from those in the initial population. T his was attributed to differential breeding accounted for by the influence of severe environmental factors. Under environmental stress, selection occu rred in the population and the mice with behavioral and neuromorphological characteristics differing from those of the control group proved to be bett er adapted to such conditions.