Swimming and reaction to electric shock in two subspecies of deermice ( Peromyscus maniculatus) during development

Abstract

The development of behaviour in Peromyscus maniculatus bairdii and P. m, gracilis was studied in two types of aversive situations. Longitudinal and cross-sectional groups of both subspecies, totalling 320 mice, were tested for the ability to escape from water and from an electrified grid. Between 16 and 22 days of age, P. m. gracilis was slower to escape from water than bairdii, but later performed like bairdii. This difference in swimming performance was attributed to differences in the rate of physical maturation of the two subspecies. The tendency to remain on top of a platform above the water was more characteristic of bairdii than of gracilis, although both subspecies increased their duration on the platform with experience in the situation. P. m. bairdii escaped from an electric shock for longer periods than gracilis. The performance of bairdii improved with accumulated experiences in this situation, while the performance of gracilis did not change appreciably. Three factors were postulated as explanations for the differences in performances of the two subspecies: rate of physical maturation, genetic determinants of behaviour, and effect of experience. Each of these factors interacts with the others to produce the adult behaviour of the mice.