The purpose of this study is to investigate the adjustment mechanism on the inter-individual distance operating to minimize social conflicts in a group. Nonoverlapping territorial system is one of the most famous examples of such mechanisms.
Five adult golden hamsters (
Mesocriecetus auratus) were used as a group, consisting of three females named F1, F2 and F3, and two males named M1 and M2. A specifically designed open-field (OF) was used to observe social interactions and to measure individual activities and the distances between each pair of subjects (Fig. 1). The experement was run for 17 days. On the fifth day, the female hamster F1 established her dominance in that group, and began to restrain the activities of the others (Fig. 2). She formed an exclusive territory of her own on one of the quarters of the open-field, and the others were vigorously expelled from it (Fig. 3, Fig. 4).
Aggressive and submissive behaviours were commonly observed among them, with a number of violent attacks occurred especially between males. One female F3 who had experienced long term isolation from weaning showed a tendency to flee from all of the others (Tables 1 and 2).
An index of proximity
Pr was used to measure spatial relations between individuals, which is approximately the inverse of the absolute distance (Fig. 5). The average proximity of the dominant female (F1) toward the others and that of the isolated female (F3) were both small (Fig. 6). This result should be explained in terms of the facts that F1 was avoided by every other, and that F3 avoided every other. Though the activities of the four subordinate members were almost the same, this did not hold for their average proximities (Fig. 7). It seemed that F3 and M2, suffering from persistent attacks by F1 and M1, adjusted their distances from the dominant subjects meticulously. So it is our conclusion that an adjustment mechanism on inter-individual distance is operating even among subordinate subjects who could not afford to have a unique territory.
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