Induced grooming transitions and open field behaviour differ in high- and low-yawning sublines of Sprague-Dawley rats

Water immersion-induced grooming sequences and open field behaviour were studied in two sublines of Sprague-Dawley rats, Rattus norvegicus, selectively bred for high(HY) and low-yawning (LY) frequency. HY rats were more active than LY rats in the open field: ambulation, rearings and wall-leanings were significantly higher in the former than in the latter group, indicating that LY rats are more emotionally reactive. Sequential analysis showed that HY rats exhibit more occurrences of a well-organized caudal grooming, while LY rats engage more frequently in well-organized facial grooming. Correspondence analysis revealed that both groups groom according to a hierarchical organization, with transitions between grooming elements depending on anatomical proximity. Clustering of grooming elements is related to a temporal recruitment and a reciprocal transition between them. Both groups, however, show distinct ‘syntaxes’ of grooming elements. Altogether these results indicate that along with a high or low frequency of yawning, there are other associated types of behaviour that separate both groups of rats. The structure of grooming between HY and LY rats indicates a strain-specific functional and neurophysiological difference. Yawning, grooming and emotional reactivity appear to be associated with arousal variations. ? 1995 The Association for the Study of Animal Behaviour In the last two decades the study of grooming has become the subject of extensive research, primarily because of its usefulness in modelling hierarchical motor control (Fentress 1988) and because grooming is structurally organized in a variety of movements that can be analysed for identifying rules that govern behavioural sequencing (Berridge 1990). This approach may provide insights into the way the central nervous system controls chains of rhythmical movements. In addition, grooming can be produced easily by either novel environments or water immersion (Jolles et al. 1979a; Colbern et al. 1981), which makes it possible to record many bouts of grooming for long periods. A variety of evidence suggests that grooming in a number of vertebrate and invertebrate species is centrally organized (Fentress 1973; Zack 1978), and that rodents groom in a cephalo-caudal progression (Richmond & Sachs 1980; Thiessen et al. 1983; Sachs 1988) which resembles the order in which grooming actions appear in developing animals (Richmond & Sachs 1980). The biological significance of grooming is still not clear, although studies indicate that it represents a de-arousal mechanism serving homeostasis (Delius 1967; Jolles et al. 1979b), and is generally considered to be a motor pattern with adaptive functions beyond the simple care of fur. Most ethological studies regarding grooming have been concerned with the analysis of its temporal patterning, mainly by the use of two methods: serial dependence and hierarchical analysis models (Dawkins & Dawkins 1976; Lefebvre 1981), the latter appear to explain the patterning of grooming better than the former (Fentress & Stilwell 1973). Detailed studies in mammals (Fentress & Stilwell 1973), insects (Dawkins & Dawkins 1976; Lefebvre 1981), and birds (van Rhijn 1977; Lefebvre & Joly 1982) have led to the suggestion that grooming is hierarchically organized, that grooming movements cluster into anterior and posterior groups according to body regions (Russell & Giles 1974; Dawkins & †To whom all correspondence should be addressed. 0003–3472/95/070061+12 $12.00/0 ? 1995 The Association for the Study of Animal Behaviour