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Introduction
Page 1
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Experiment 1:
Intro/Method
Pages 2-3
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Experiment 1:
Results
Page 4
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Experiment 1:
Discussion
Page 5
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Experiment 2:
Intro/Method
Page 6
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Experiment 2:
Results
Page 7
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Experiment 2:
Discussion
Page 8
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Experiment 3:
Intro/Methods
Page 9
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Experiment 3:
Results
Page 10
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Experiment 3:
Discussion
Page 11
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General Discussion
Page 12
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Figures 1-2-3
Pages 13-14-15
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Tables 1-2-3
Pages 16-17-18
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Competitive fighting was readily obtained under the experimental conditions. The highest rate of fighting was by DA females: all DA females fought on at least one test, and 14 of the 16 fought in half or more of all tests. The mean attack frequency (bite-and-kick and bite attacks) for normal DA females was 1.86. The lowest rate of fighting was by Fischer rats with normal females, having a mean attack frequency of 0.11 and normal males 0.16. Because fighting by the Fischers was infrequent, most of the data analysis below concerns only the DA rats.
All categories of rats showed all of the various motor patterns of offense, including bite-and-kick attack, bite attack, and offensive sideways posture. On-top posture was often observed as well, which is often interpreted as an unconsummated bite-and-kick attack. Upright posture was often observed, but most frequently as a defensive response by the victim of the attack. Piloerection was difficult to measure and was not analyzed, while chase was rarely seen because of the small dimensions of the cage. Attacks were more or less equally distributed between bite-and-kick attacks and bite attacks in all categories.
Contrary to the prediction from the model, rats did not tend to fight more against opponents of the same sex. Instead, both males and females and both normal and gonadectomized rats attacked female opponents significantly more than male opponents (F = 4.74, p = 0.029). This was consistent across all categories of test animals as may be seen in Table 1 and Fig. 1. For example, normal males had a mean attack frequency of 0.91 against females and 0.67 against males, the opposite of what the model would have predicted.
Females fought more than males. The difference was greatest in the normal animals, but persisted in gonadectomized animals as well. As shown in Table 1 and Fig. 1, normal females had an attack frequency of 1.86, while normal males had a frequency of 0.79. Ovariectomized females had a mean attack frequency of 0.92, while castrated males had a frequency of 0.58. The sex difference was highly significant (F = 22.6, p < 0.001 ).
Gonadectomy significantly reduced offense in both males and females. The difference was highly significant (F = 15.0, p <0.001). As shown in Table 1 and Fig. 1, male attacks were reduced by castration from 0.79 to 0.58, while female attacks were reduced by ovariectomy from 1.86 to 0.92. The effect of surgery was significantly greater in the females than in the males, as indicated by the interaction of sex by surgery in the analysis of variance (F = 5.5, p = 0.019).
Although there was a tendency towards more fighting at 48-h deprivation than at 24-h deprivation for both normal and gonadectomized rats, the difference was not statistically significant by the analysis of variance. The mean attack frequency for all rats at 48-h deprivation was 1.13, while the mean at 24-h deprivation was 0.94.
In the analysis of variance, the only two-way interaction of any significance was sex by surgery, and there was only one significant three-way interaction (test order by sex of opponent by sex of test animal).
The data for offensive sideways posture tended to parallel the data for mean attack frequency in most, but not all respects. Thus, females had higher overall rates than males of both normal and gonadectomized rats (0.53 compared to 0.38) and normals, both females and males, had higher rates than gonadectomized animals (0.66 compared to 0.26). However, there was a tendency for rats to have higher rates of offensive sideways posture against male than against female opponents (0.49 compared to 0.42 including all rats); this was the opposite of the data for attack frequency, which was greater against female opponents.
The data for Fischers were too low to draw conclusions from, but there were tendencies similar to those of the DA rats. Both males and females were more likely to attack female opponents. Including both normal and tube-tied Fischers, the mean attack frequencies were 0.13 and 0.11 for males and females, respectively, against female opponents and 0.10 and 0.02 for males and females, respectively, against male opponents (see Table 1). In most cases, a dominance relationship was established in the warm up tests, after which the Fischers tended to be defensive in response to the attacks of their DA cagemates.
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