The agnostic behaviour of Rattus villosissimus

Abstract

The agonistic behaviour of male-male (MM), female-female (FF), and male-female (MF) pairs of R. villosissimus was recorded and analysed. Most of the 300 observed encounters were of 15 min duration. The analysed acts and postures are described. Data are presented on: outcome of en- counters; frequency and location of injuries; response frequency and duration per encounter; temporal change in activity; analysis of sequences; principal components analysis. Ninety-five per cent of MF encounters, 92% of FF encounters and 70% of MM encounters contained some aggressive acts or postures. MM encounters had the greatest frequency and duration of agonistic behaviour. FF encounters had more agonistic behaviour than MF encounters. Cuts in the skin were caused by 27.6% of bites in MM encounters, but not by bites in MF or FF encounters. Displacement acts were most frequent in MF encounters. Dominant rats rarely performed acts associated with subordination and vice versa. Temporal analyses showed that encounters could be divided into three phases: (1) the activity was most intense and dominance-subordination behaviour was established, often without physical contact; (2) there was a decline in activity; (3) the animals associated less and performed more non-agonistic behaviour. Each phase can be characterized by the predominance of certain groups of behavioural patterns. A principal components analysis supported this grouping of responses. The so-called 'submissive' posture in this species increased rather than decreased aggressive acts. An analysis of sequences revealed many links of behavioural patterns. There was, however, no fixed chain of responses. Considerable behavioural lability exists as a result of both rats modifying their actions according to those of their opponents.