Stereotypies in Laboratory Mice — Quantitative and Qualitative Description of the Ontogeny of ‘Wire‐gnawing’ and ‘Jumping’ in Zur:ICR and Zur:ICR nu

摘要

AbstractThe ontogeny of two stereotypic patterns, wire‐gnawing and jumping, was studied in 24 laboratory mice: six males and six females each of two closely related outbred strains, kept under standard housing conditions, a conventional albino strain (ICR) and a nude, athymic mutant (ICR nu; hereafter: NU). All 24 individuals developed wire‐gnawing after weaning at 20 d of age. In ICR one female and in NU five males and three females additionally developed jumping. ICR developed wire‐gnawing between the age of 20 and 30 d, in NU jumping started at the age of 20 d, but intense jumping and wire‐gnawing comparable to that of ICR did not develop in NU before the age of 40–50 d. Within each strain there was no significant difference between males and females with respect to the development of stereotypic behaviour. By contrast, ICR showed significantly more wire‐gnawing but less jumping than NU.Stereotypy level increased with age up to a mean of 10.7 of total activity in ICR and up to 7.4 in NU at 100 d of age. However, there was huge inter‐ and intra‐individual variability with respect to all parameters assessed in this study, i.e. total duration, number of bouts and bout length of the two stereotyped patterns.Wire‐gnawing developed from outside‐directed explorative climbing at the cage lid, whereas thesource behaviour pattern(Mason 1991 a, Anim. Behav. 41, 1015–1037) of jumping was outside‐directed explorative rearing at the cage wall. At 20 d of age, before the onset of stereotypy development, ICR showed significantly more climbing but less rearing than NU. Physical retardation of NU at weaning may account for decreased climbing ability during early ontogeny, and hence for the retarded development of wire‐gnawing. The difference in early experience with either of the two patterns rather than genetic effects may be responsible for the qualitative difference between the strains with respect to the