Puglesi-Allegra et al., 1990; Skrinskaya et al., 1992; Tolliver et al., 1994; Golden et al., .
1995; Morimasa et al., 1995; Sluyter et al., 1995; Ballas et al., 1996 . The literature provides numerable examples on successful selection for normal
Ž behaviour as well as non-stereotypic behavioural disorders e.g. Bruell, 1962; Murphree
et al., 1967; Peters et al., 1967; Symons and Sprott, 1976; McCaffrey et al., 1980; .
McDonough et al., 1981; Plomin, 1990; Benus et al., 1991; Rosengarten et al., 1994 . The present study aimed at examining the possible genetic basis of stereotypies in the
bank vole. Laboratory- bred, but not wild caught, bank voles housed isolated in barren cages develop high frequencies of locomotor stereotypies, including easily recognisable
¨
Ž backwards somersaulting, jumping, and windscreen wiper movements Odberg, 1986;
. Sørensen, 1987; Sørensen and Randrup, 1986; Cooper and Nicol, 1991, 1994 . We
Ž .
repeated this finding in our recent study Schoenecker et al., 2000 on wild caught Ž
. Ž
. Danish voles P: n s 92 and their laboratory-bred offspring F1: n s 248 . While none
of the wild caught voles showed stereotypies under isolation, 74 or 30 of the F1 offspring developed stereotypies at the average age of 96 days. In the present study,
voles from the abovementioned F1 generation were chosen for selective matings between non-stereotypers and stereotypers. The subsequent development of stereotypic
Ž .
behaviour in the resulting offspring F2 was then compared with the stereotypy status of their parents when the fathers were removed at the day of delivery. Moreover, we
attempted to evaluate a possible influence of social facilitation by keeping the litters together after weaning for variable lengths of time before isolation and relate this to
subsequent development of stereotypies.
2. Materials and methods
2.1. Animals, housing and breeding The animals in the present study consisted of two successive laboratory-bred genera-
Ž .
Ž .
tions of bank voles representing F1 n s 248 and F2 n s 270 of an originally wild caught stock.
Ž .
F1 individuals 138 males and 110 females from 52 different litters were weaned at the age of 36 days and transferred to individual housing in small barren cages of
Ž
3
. Ž
. transparent plastic 13.5 = 16.0 = 22.5 cm
under a 12-h light regime 0800–2000 h . The cages were supplied with a woodcutting bed and the voles had access to food
Ž .
standard rat chow and water ad libitum. Cage cleaning was performed every second week or when necessary, and a portion of a grain mixture was given when the cages
were cleaned. The animals were kept under these conditions for at least 180 days, except for short
breeding sessions. Mating pairs were selected according to the possible four combina- tions of stereotypic or non-stereotypic males and females and transferred to larger
Ž
3
. enriched cages 14.5 = 21.5 = 37.5 cm
supplied with woodcutting bed, toilet paper and card board rolls. Breeding males were returned to isolation at the day of delivery.
Ž .
The resultant offspring F2 consisted of 138 males and 132 females in 58 different litters. Equal numbers of litters from each of the four possible mating pair combinations
were either weaned at the age of 20 days and allowed company with their littermates for 12 days before transference to isolation, or they were weaned at the age of 32 days and
immediately transferred to isolation. The isolation period for F2 pups lasted until they reached the age of 180 days after which the study was terminated.
2.2. ObserÕations and classification The occurrence of stereotypic behaviour was examined before and after isolation by
one-zero sampling every 15 min for 3–4 h every day during the whole study period. When stereotypies were recognisable, the age and sex of the voles were noted along
Ž . with the type of stereotypy performed. Voles were classified as stereotypers S if
individual stereotypic behaviour were noted in bouts of at least five repetitions during the daily observation periods. These bouts, separated by small intervals, could continue
Ž .
for hours. The classification S covered voles showing backward somersaulting BS , Ž
. Ž
. high speed jumping JUMP , pacing following a fixed route PF and windscreen wiper
¨
Ž .
Ž .
Ž .
movements WIN as previously defined by Odberg 1986 , Sørensen 1987 , Sørensen Ž
. Ž
. and Randrup
1986 , and Cooper and Nicol 1991, 1996 . Voles neither showing
Ž . stereotypies nor polydipsia were classified as non-stereotypers N .
At the end of the study, the proportion of voles classified as S and N in F2 was calculated and related to the development of stereotypies in their parents. This allowed
investigation of stereotypy development among the offspring of the following four possible F1 mating groups: N male mating N female, S male mating N female, N male
mating S female, and S male mating S female. Some voles in F1 developed severe
Ž polydipsia after delivery and the age of 180 days
water intake 21 mlrday vs. .
normally 10 mlrday . The offspring of these voles were omitted from the present study, Ž
. leaving 187 F2 voles 93 males and 94 females in 42 litters for further data treatment.
2.3. Statistical analyses Differences in proportions of voles classified as S or N in F1 and F2 were tested by
chi square tests using Yates continuity correction factor when n - 20. Spearman rank Ž
. correlation tests corrected for ties were used to estimate effects of isolation age on
stereotypies. The chosen significance level was 0.05 and all tests were two-tailed.
3. Results
