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Blinding increases territorial aggression in male syrian golden hamsters
BEHAVIORAL BIOLOGY 17, 139-141 (1976), Abstract No. 5269
BRIEF REPORT B l i n d i n g I n c r e a s e s T e r r i t o r i a l A g g r e s s i o n in Male Syrian Golden Hamsters
MICHAEL R. MURPHY 1,2
Department of Psychology, Massachusetts Institute of Technology, Cambridge, Massachusetts The effects of enucleation (blinding) on the territori~ aggression of male Syrian golden hamsters were studied. While enucleated hamsters were as likely as controls to attack, their duration of attacking was much greater than that of controls. Thus, in contrast to the initiation of aggression in hamsters, which is mainly under olfactory control, the termination of aggression is partially regulated by vision.
The initiation of territorial aggression in male Syrian golden hamsters is greatly influenced by olfactory stimuli and is almost completely eliminated by centrally or peripherally produced olfactory impairment (Devor and Murphy, 1973; Murphy, 1973; in press; Murphy and Schneider, 1970). In contrast, the termination o f aggression in this species is thought to be influenced b y visual stimuli. It has been hypothetized that postures which serve to display or conceal the black markings on hamsters' chests indicate relative submission or aggression (Grant and Mackintosh, 1963). Grant, Mackintosh, and Lerwill (1970) have shown that hamsters with artificially enhanced chest markings have an aggressive advantage over untreated hamsters. The present experiment examined the importance of visual stimuli to aggressive behavior in hamsters by studying the response of blinded hamsters to an intruder into the home cage. Twenty-six highly aggressive subjects were selected from a group o f 20 normal and 20 unilaterally olfactory bulbectomized hamsters which had served as control subjects in a previous study. These subjects were assigned to two groups o f 13 that were matched for time spent attacking; about one-half of 1These data were collected while the author was supported by an NSF predoctoral fellowship and were prepared for publication while he was an NIMH Staff Fellow at the Laboratory of Brain Evolution and Behavior. I thank P. D. MacLean, J. E. Murphy, and A. T. Nunez for their comments on this manuscript. 2Present address: Laboratory of Brain Evolution and Behavior, NIHAC-110, National Institute of Mental Health, Bethesda, Maryland 20014. 139 Copyright (~)1976 by Academic Press, Inc. All rights of reproduction in any form reserved.
140
MICHAEL R. MURPHY
each group was unilaterally bulbectomized and one-half was normal. Members of one group were enucleated under deep anesthesia. Starting 1 week after the enucleation, the territorial aggression of each hamster was tested four times, with 2 days between tests. At the start of a test the experimental hamster was removed from his home cage; a nonaggressive opponent was then put into the cage, and the experimental hamster was returned to his cage where he found the intruder. Nonaggressive opponent hamsters were selected for a low level of aggression and were further standardized by removing their olfactory bulbs bilaterally. Such a treatment reduces the possibility that the opponent hamsters will initiate aggression (Murphy and Schneider, 1970). Results were analyzed using a two-tailed t test. The average attack time per 300 sec test was much greater for blind hamsters (143.7 sec) than for hamsters with intact vision (85.9 sec, P < 0.001) (See Fig. 1). The two groups, however, did not differ in the percentage of tests in which at least 5 sec of attack occurred (86.5% for hamsters with intact vision and 86.3% for blind hamsters, P > 0.05). The average attack time for blind hamsters was significantly higher on the last two trials than on the first two trials (165.6 vs. 121.8 sec, P < 0 . 0 1 ) ; on the same comparison, the behavior of normal hamsters did not differ (85.7 vs. 86.1 sec, P > 0.05). Blind and intact hamsters did not significantly differ in the average time spent investigating an intruder (135.0 and 110.8 sec, respectively, P > 0.05). Thus, blind hamsters were as likely as controls to initiate attack, but continued attacking for much longer than did controls. One interpretation of these results is that visually perceived stimuli from other hamsters act to
160
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Normal qn=13
...........
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Blinded in=13
."
140
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120
~
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60-
4020-
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I
0
1
PREOPERATIVE
~ _ _ 2
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3
4
POSTOPERATIVE TEST NUMBER
TEST
Fig. 1. Effects of blinding on the terntorial aggression o f male Syrian golden hamsters. Points o n t h e graph signify the m e a n attack duration (per 300 sec test) of blinded and n o r m a l hamsters o n one preoperative and four postoperative tests o f response to a territorial intruder.
BLINDING AND AGGRESSION IN HAMSTERS
141
inhibit aggression. This interpretation is consistent with the findings o f Grant, Mackintosh, and Lerwill (1970) described earlier. An alternate explanation is that these results were due to hormonal changes. This is unlikely for two reasons. First, testing was completed within 15 days of enucleation, before significant testicular atrophy caused by enucleation has been reported to occur (Reiter,. 1968). Second, a reduction in testosterone level (induced by castration) has been reported to decrease, not increase, aggression in hamsters (Payne and Swanson, 1972; Vandenbergh, 1971). Earlier work has demonstrated that olfactory stimuli are extremely important in eliciting territorial aggression in hamsters (Murphy, 1973; in press; Murphy and Schneider, 1970). The results reported here suggest that visual stimuli are important for the inhibition of territorial aggression. In the wild, hamsters are solitary, fossorial rodents which maintain food hoards that are probably necessary for their survival. Since hamsters in the laboratory exhibit vigorous defense of the home cage (Murphy, in press) it is reasonable to assume that hamsters in the wild defend their home tunnel systems. There, in the dark, olfactory stimuli would be sufficient to elicit an attack. Aggression might then continue until the intruder has been forced aboveground where visual stimuli from postures and markings would be perceived. Only then might the defending hamster react to the submissive visual signals o f the intruder.
REFERENCES Devor, M., and Murphy, M. R. (1973). The effect of peripheral olfactory blockade on the social behavior of the male golden hamster. Behav. Biol. 9, 31-42. Grant, E. C., and Mackintosh, J. H. (1963). A description of the social postures of some laboratory rodents. Behaviour 21, 246-259. Grant, E. C., Mackintosh, J. H., and Lerwill, C. J. (1970). The effect of a visual stimulus on the agonistic behaviour of the golden hamster. Z. Tierpsychol. 28, 73-77. Murphy, M. R. (1973). Effects of female hamster vaginal discharge on the behavior of male hamsters. Behav. Biol. 9, 367-375. Murphy, M. R. Olfactory stimulation and olfactory bulb removal: Effects on territorial aggression in male Syrian golden hamsters. Brain Res., in press. Murphy, M. R., and Schneider, G. E. (1970). Olfactory bulb removal eliminates mating behavior in the male golden hamster. Science 167, 302-304. Payne, A. P., and Swanson, H. H. (1972). The effect of sex hormones on the agonistic behavior of the male golden hamster (Mesocricetus auratus Waterhouse). Physiol. Behav. 8, 687-691. Reiter, R. J. (1968). Morphological studies on the reproductive organs of blinded male hamsters and the effects of pinealectomy or superior cervical ganglioneetomy. Anat. Rec. 160, 13-24. Vandenbergh, J. G. (1971). The effects of gonadal hormones on the aggressive behaviour of adult golden hamsters (Mesocricetus auratus). A nim. Behav. 19, 589-594.
BRIEF REPORT B l i n d i n g I n c r e a s e s T e r r i t o r i a l A g g r e s s i o n in Male Syrian Golden Hamsters
MICHAEL R. MURPHY 1,2
Department of Psychology, Massachusetts Institute of Technology, Cambridge, Massachusetts The effects of enucleation (blinding) on the territori~ aggression of male Syrian golden hamsters were studied. While enucleated hamsters were as likely as controls to attack, their duration of attacking was much greater than that of controls. Thus, in contrast to the initiation of aggression in hamsters, which is mainly under olfactory control, the termination of aggression is partially regulated by vision.
The initiation of territorial aggression in male Syrian golden hamsters is greatly influenced by olfactory stimuli and is almost completely eliminated by centrally or peripherally produced olfactory impairment (Devor and Murphy, 1973; Murphy, 1973; in press; Murphy and Schneider, 1970). In contrast, the termination o f aggression in this species is thought to be influenced b y visual stimuli. It has been hypothetized that postures which serve to display or conceal the black markings on hamsters' chests indicate relative submission or aggression (Grant and Mackintosh, 1963). Grant, Mackintosh, and Lerwill (1970) have shown that hamsters with artificially enhanced chest markings have an aggressive advantage over untreated hamsters. The present experiment examined the importance of visual stimuli to aggressive behavior in hamsters by studying the response of blinded hamsters to an intruder into the home cage. Twenty-six highly aggressive subjects were selected from a group o f 20 normal and 20 unilaterally olfactory bulbectomized hamsters which had served as control subjects in a previous study. These subjects were assigned to two groups o f 13 that were matched for time spent attacking; about one-half of 1These data were collected while the author was supported by an NSF predoctoral fellowship and were prepared for publication while he was an NIMH Staff Fellow at the Laboratory of Brain Evolution and Behavior. I thank P. D. MacLean, J. E. Murphy, and A. T. Nunez for their comments on this manuscript. 2Present address: Laboratory of Brain Evolution and Behavior, NIHAC-110, National Institute of Mental Health, Bethesda, Maryland 20014. 139 Copyright (~)1976 by Academic Press, Inc. All rights of reproduction in any form reserved.
140
MICHAEL R. MURPHY
each group was unilaterally bulbectomized and one-half was normal. Members of one group were enucleated under deep anesthesia. Starting 1 week after the enucleation, the territorial aggression of each hamster was tested four times, with 2 days between tests. At the start of a test the experimental hamster was removed from his home cage; a nonaggressive opponent was then put into the cage, and the experimental hamster was returned to his cage where he found the intruder. Nonaggressive opponent hamsters were selected for a low level of aggression and were further standardized by removing their olfactory bulbs bilaterally. Such a treatment reduces the possibility that the opponent hamsters will initiate aggression (Murphy and Schneider, 1970). Results were analyzed using a two-tailed t test. The average attack time per 300 sec test was much greater for blind hamsters (143.7 sec) than for hamsters with intact vision (85.9 sec, P < 0.001) (See Fig. 1). The two groups, however, did not differ in the percentage of tests in which at least 5 sec of attack occurred (86.5% for hamsters with intact vision and 86.3% for blind hamsters, P > 0.05). The average attack time for blind hamsters was significantly higher on the last two trials than on the first two trials (165.6 vs. 121.8 sec, P < 0 . 0 1 ) ; on the same comparison, the behavior of normal hamsters did not differ (85.7 vs. 86.1 sec, P > 0.05). Blind and intact hamsters did not significantly differ in the average time spent investigating an intruder (135.0 and 110.8 sec, respectively, P > 0.05). Thus, blind hamsters were as likely as controls to initiate attack, but continued attacking for much longer than did controls. One interpretation of these results is that visually perceived stimuli from other hamsters act to
160
-
-
Normal qn=13
...........
.*
Blinded in=13
."
140
/"
120
~
..~- -
60-
4020-
~
g, !
I
0
1
PREOPERATIVE
~ _ _ 2
I__
I
3
4
POSTOPERATIVE TEST NUMBER
TEST
Fig. 1. Effects of blinding on the terntorial aggression o f male Syrian golden hamsters. Points o n t h e graph signify the m e a n attack duration (per 300 sec test) of blinded and n o r m a l hamsters o n one preoperative and four postoperative tests o f response to a territorial intruder.
BLINDING AND AGGRESSION IN HAMSTERS
141
inhibit aggression. This interpretation is consistent with the findings o f Grant, Mackintosh, and Lerwill (1970) described earlier. An alternate explanation is that these results were due to hormonal changes. This is unlikely for two reasons. First, testing was completed within 15 days of enucleation, before significant testicular atrophy caused by enucleation has been reported to occur (Reiter,. 1968). Second, a reduction in testosterone level (induced by castration) has been reported to decrease, not increase, aggression in hamsters (Payne and Swanson, 1972; Vandenbergh, 1971). Earlier work has demonstrated that olfactory stimuli are extremely important in eliciting territorial aggression in hamsters (Murphy, 1973; in press; Murphy and Schneider, 1970). The results reported here suggest that visual stimuli are important for the inhibition of territorial aggression. In the wild, hamsters are solitary, fossorial rodents which maintain food hoards that are probably necessary for their survival. Since hamsters in the laboratory exhibit vigorous defense of the home cage (Murphy, in press) it is reasonable to assume that hamsters in the wild defend their home tunnel systems. There, in the dark, olfactory stimuli would be sufficient to elicit an attack. Aggression might then continue until the intruder has been forced aboveground where visual stimuli from postures and markings would be perceived. Only then might the defending hamster react to the submissive visual signals o f the intruder.
REFERENCES Devor, M., and Murphy, M. R. (1973). The effect of peripheral olfactory blockade on the social behavior of the male golden hamster. Behav. Biol. 9, 31-42. Grant, E. C., and Mackintosh, J. H. (1963). A description of the social postures of some laboratory rodents. Behaviour 21, 246-259. Grant, E. C., Mackintosh, J. H., and Lerwill, C. J. (1970). The effect of a visual stimulus on the agonistic behaviour of the golden hamster. Z. Tierpsychol. 28, 73-77. Murphy, M. R. (1973). Effects of female hamster vaginal discharge on the behavior of male hamsters. Behav. Biol. 9, 367-375. Murphy, M. R. Olfactory stimulation and olfactory bulb removal: Effects on territorial aggression in male Syrian golden hamsters. Brain Res., in press. Murphy, M. R., and Schneider, G. E. (1970). Olfactory bulb removal eliminates mating behavior in the male golden hamster. Science 167, 302-304. Payne, A. P., and Swanson, H. H. (1972). The effect of sex hormones on the agonistic behavior of the male golden hamster (Mesocricetus auratus Waterhouse). Physiol. Behav. 8, 687-691. Reiter, R. J. (1968). Morphological studies on the reproductive organs of blinded male hamsters and the effects of pinealectomy or superior cervical ganglioneetomy. Anat. Rec. 160, 13-24. Vandenbergh, J. G. (1971). The effects of gonadal hormones on the aggressive behaviour of adult golden hamsters (Mesocricetus auratus). A nim. Behav. 19, 589-594.