Introduction and Method
This experiment was designed to determine if the pattern of territorial fighting as a function of opponent sex is similar in DA rats to the pattern found by previous investigators using other strains of rats. Previous investigators (8, 10) have found that normal males attack male intruders at a much higher rate than female intruders, while the opposite is true for females, who attack female intruders at a much higher rate.
Subjects and housing. Tests were conducted on eight pairs of DA rats, one male and one female, who were housed in enriched environments. The mean weights were 287 and 197 g for DA males and females, respectively. The cages were constructed of wire mesh 161 X 25 cm with Plexiglas fronts. Each cage was divided by a partition with a door in the center, and one side contained a nest box that was of solid metal 20 x 20 cm connected to the rest of the cage by a wire mesh tunnel 20 cm long and 7 cm in diameter. The floor of the cage was covered with wood chips. Intruder rats consisted of an outbred hooded strain (SFD) developed through the crossing of the DA agouti, Fischer albino and an S2 black strain. The mean weights of SFD males and females were 305 and 210 g, respectively. They were housed in groups of three in cages similar to those described in Experiment 1. Lighting was similar to Experiment 1.
Experimental design. The experiment was conducted for 4 weeks. Twice each week an SFD outbred intruder was introduced into the cage of each resident DA pair and the resultant behaviors of all rats (the two residents and the intruder) were recorded for 20 min, after which time the intruder was put back into its home cage. In one test each week the intruder was a male, and in the other test the intruder was a female. The following behaviors were recorded: bite-and-kick attack, bite attack, offensive side-ways posture, upright posture, on-top posture, chase, and mounting. Testing was done at a time 3 h into the dark cycle. Observations and weighing were conducted as in Experiment 1.
Statistical Analysis. A repeated measures analysis of variance was carried out on the attack frequency data (not transformed) with three main effects: test order, sex of opponent, and sex of test animal.