Brief communicationEffects of weasel odor on behavior and physiology of two hamster species
Introduction
Numerous studies have revealed that rodents' avoidance of predator odors as aversive stimuli or predator cues seems to be innate and could be reinforced by encounters with the predator [10], [11]. Exposures of rodents to predator odors can cause the elevation in the glucocorticoid level and/or the enlargement of the adrenal gland [4], [5]. Nevertheless, previous findings on the effects of a predator or its odor on reproductive conditions of prey are inconsistent [1], [9], [13]. The disagreement might be partially due to the methodological aspects in laboratory and field studies. Specifically, few studies have investigated behavioral and physiological stress in the voles induced by chronic presence of predator odors [4], [13]. No attempt has so far been available to examine the effect caused by excessive exposure of predator odors.
The Siberian weasel (Mustela sibirica) is mainly distributed in China and the neighboring countries [6]. In North China, the Siberian weasel is a key natural predator of the ratlike hamster (Cricetulus triton) and they are sympatric in distribution. The golden hamster (Mesocricetus auratus) was originally distributed in the Middle East and Eastern Europe and is now a common laboratory animal without natural ecological relevancy with Siberian weasels. These two hamsters are both solitary and share numerous similarities such as body size, having the flank gland, and behavioral patterns [7], [15]. In this study, we attempted to examine how predator odor exposure affects the level of aggression and physiological conditions in the two species of hamsters through a long-term presentation of overdose of anal gland secretion of the weasels, the malodorous sulfur-containing compounds.
Section snippets
Methods and materials
Twenty male adult ratlike hamsters and 20 male adult golden hamsters were used as the test subjects. The ratlike hamsters were captured by live traps in the farmland in central Hebei Province, North China, in April (breeding season), 2000. The golden hamsters (90–120 days old) were bred at the Laboratory of Animal Services, Chinese Academy of Preventative Medical Science. Animals in the control and experimental groups were housed separately and caged individually in plastic cages (40×25×15 cm)
Results
For both ratlike and golden hamsters, individuals in the control group consistently defeated individuals in the experimental group for conspecifics. The hamsters in the control groups initiated attacks more frequently (male ratlike hamster: Z=2.199, P<.05; golden hamsters: Z=2.293, P<.05) and displayed defensive behavior less often (Male ratlike hamsters: Z=2.192, P<.05; male golden hamsters: Z=2.311, P<.05, see Fig. 1, Fig. 2).
In ratlike hamsters, the experimental group displayed less flank
Discussion
Our results confirmed that psychological stressors have negative effects on some aspects of the rodents' behavior and physiology [1], [4], [5]. Specifically, we found that the aggression level of both hamsters in the experimental groups was lowered after long-term exposure to the weasel odor. This negates the previous finding that acute exposure of rodents to predator odors would increase the aggression [4].
Exposures to psychological stressors are likely to cause glucocorticoid level elevation
Acknowledgments
We express our gratitude to the Beijing Institute of Immunoassay for hormonal immunoassay and S. Wang, F. Wang, X. Cao, and T. Xu for their assistance in capturing and caring for ratlike hamsters. Mr. Kevin Bruce provided valuable comments on the paper. The work was supported by the grants from Chinese NSF (39970110, 39730090, and 39825105), Chinese Academy of Sciences (KSCX2-1-03, STZ-01-06, KSCX2-SW-103, and KSCX2-SW-105), and Ministry of Science and Technology (FS2000-009).
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