Motivational Systems in Muroid Rodents

Piloerection often accompanies offensive postures, particularly the offensive sideways posture. Like locomotor activity which may accompany this posture, the piloerection may serve to enhance and accentuate the posture and thereby increase its effectiveness as a threat. Piloerection has been specifically described as an accompaniment of offense in M musculus [Scott and Fredericson, 1951], M agrestis [Clarke, 1956], R norvegicus [Barnett, 1958a], P maniculatus [Balph and and Stokes, 1960], L lemmus [Arvola et al, 1962], A sylvaticus and flavicollis [Montgomery, 1978], and N alexis [Stanley, 1971]. Eibl-Eibesfeldt [1951] reported that it was not distinct during offense in Meriones persicus.

Several other acts and postures that function as threats have been reported with offense in only a few muroid rodent species. Teeth-chattering occurs in offense in L lemmus [Arvola et al, 1962], M agrestis [Clarke, 1956], Rhombomys opimus [Goltzman et al, 1977] , R norvegicus [Barnett, 1958a], R villosissimus [Begg, 1975], R fuscipes [Barnett and Stewart, 1975], D groenlandicus [Brooks and Banks, 1973], and most species of Peromyscus [Clark and Schein, 1966] and Otomys irroratus [Davis, 1972]. Both of these can be ambivalent motor patterns. Teeth-chattering and tail-rattling in some species are motor patterns of defense.

Active secretion or extrusion of pheromones may occur as a motor pattern of offense. During the intermale encounters of R norvegicus, there is an increase in flank-grooming by the home rat and of investigation of his flank by the intruder rat, which we have interpreted as evidence for active flank-gland secretion as a motor pattern of offense [Lehman and Adams, 1977]. Similarly, flank rub occurs during and after offense in Me auratus [Johnston, 1977a] and R norvegicus [Adams, 1976], suggesting that this also may be a response contingent upon the secretion of pheromones from the flank glands during offense.

Several other motor patterns, sometimes attributed to offense, are more likely due to activation of other motivational systems. Although many authors have described biting of the face as part of "aggression," they were probably describing the lunge-and-bite attack of defense, as will be described below, rather than offense. Audible vocalizations, such as squeals and the "chit" vocalizations that accompany the lunge-and-bite attack are also probably due to defense activation rather than indicating offense. With the exception of R villosissimus which vocalizes with "coughing" and "hissing" during offense [Begg, 1975], muroid rodents are generally silent during offense and vocalize only during defense. The short-pulse ultrasonic vocalizations which may accompany offense [Sales and Pye, 1974] may occur as an automatic accompaniment of locomotion rather than being specific to offense, and may function for echolocation [Buchler, 1976]. Finally, allogrooming, which has been classified as "aggressive" by a number of authors [Grant and Mackintosh, 1963; Kahn, 1954; Allin and Banks, 1968], is probably a complex ambivalent motor pattern of other motivational systems [Lehman and Adams, 1977]. It is not correlated with threat and chase in Peromyscus [Healey, 1967] or "aggressiveness" in M musculus [Southwick and Clark, 1968], and has a different time course than offense as a function of social isolation in M musculus [Poshivalov, 1974]. And allogrooming occurs in other contexts besides those with offense [Barnett, 1975; Scott and Frederickson, 1951; Clark and Schein, 1966].