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The development of stereotypies and polydipsia was studied in wild caught bank voles (P: n=92) and their laboratory-bred offspring (F1: n=248). All animals were kept isolated in barren cages in the laboratory. In the P generation, no individuals developed stereotypies, but 22% developed polydipsia (>21 ml/day water intake against normally 10 ml/day). Polydipsia was more frequent among males (34%) than females (13%). In F1, 30% developed locomotor stereotypies alone, 21% showed polydipsia alone, and, additionally, 7% developed both stereotypies and polydipsia. Fewer males than females developed stereotypies (23% vs. 38%), whereas polydipsia was more frequent in males than in females (30% vs. 11%). The occurrence and distribution of polydipsia among sexes were the same in F1 and P. The distribution of different types of stereotypies in stereotyping voles were backward somersaulting (BS, 80%), high-speed jumping (JUMP, 29%), pacing following a fixed route (PF, 12%) and windscreen wiper movement (WIN, 5%). Some individuals (10%) showed two or more different types of stereotypies. The average age for developing stereotypies was 96 days while polydipsia was registered at the age of 63 days in both sexes. Voles showing both polydipsia and stereotypies developed polydipsia later (79 days) than polydipsic voles not showing stereotypies. This difference was especially pronounced in stereotyping females in which the occurrence of polydipsia was postponed to the age of 114 days. Polydipsic voles were tested positive for glucosuria indicating that polydipsia could be a symptom of diabetes mellitus. It is suggested that the development of stereotypies and polydipsia among bank voles in the laboratory are the results of frustration and prolonged stress. Stereotypies seem to depend on frustrative experiences early in life, while polydipsia may be related to diabetes mellitus caused by the experience of prolonged stress. Moreover, circumstances related to the development of stereotypies may be adaptive by reducing the risks of prolonged stress, including the development of fatal polydipsia. |
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