Zhi-Bin Zhang

Effects of weasel odor on behavior and physiology of two hamster species.

This study examined the behavioral and physiological effects of long-term exposure to overdose of aversive odor (predator odor) in two species of hamsters. About 0.05 mg of anal gland secretions of Siberian weasels (Mustela sibirica) was smeared at the oronasal groove of wild male ratlike hamsters (Cricetulus triton) (natural prey) and laboratory golden hamsters (Mesocricetus auratus) once every day for 4 weeks. After 28 days, the experimental groups of both hamster species displayed higher cortisol level, larger adrenal gland (in ratlike hamsters only), smaller thymus and flank gland, and lower aggression level than the conspecific control group (presented with water). Thus, the long-term presence of overdose of the anal gland secretion of the Siberian weasel could lower the aggression and social rank and suppress the immunity in the hamsters. The reproductive conditions of these prey species, however, seemed not to be affected. In addition, the similarities in the behavioral and physiological responses to the predator odor between the two species of hamsters showed that the responses to predator odor might be innate.

Volatile Compounds in Anal Gland of Siberian Weasels (Mustela sibirica) and Steppe Polecats (M. eversmanni)

The volatile constituents in anal gland secretions of two sympatric Mustela species, the Siberian weasel (M. sibirica) and steppe polecat (M. eversmanni), were studied by the headspace technique, followed by gas chromatography–mass spectrometry (GC-MS) analysis. Nine sulfur-containing compounds were identified. They were 2,2-dimethylthietane, (Z)- or (E)-2,4-dimethylthietane, (E)-2,3-dimethylthietane, 2-ethylthietane, (E)-2-ethyl-3-methylthietane, (Z)-2-ethyl-3-methylthietane, 2-propylthietane, 3,3-dimethyl-1,2-dithiacyclopentane, and (Z)-3,4-dimethyl-2,2-dithiacyclopentane. Among them, (E)-2-ethyl-3- methylthietanes, (Z)-2-ethyl-3-methylthietanes, and (Z)-3,4-dimethyl-1,2-dithiacyclopentane were present in the polecat but not in the weasel. The predominant compound was 2,2-dimethylthietane in the weasel and (E)- or (Z)-2,4-dimethylthietane in the polecat. These differences were consistent between the two species, regardless of sex and age and, therefore, could possibly be used for species recognition. In the weasel, 2-ethylthietane was found only in the female, and the relative abundance of several compounds was significantly different between males and females. In the polecat, although no sex-specific volatile compounds were found, males and females differed in the relative abundance of several of the compounds. In both species, the relative abundance of some compounds varied with age. We conclude that these volatile compounds can be used to communicate information about species, sex, and age.

Food restriction in pregnant rat-like hamsters (Cricetulus triton) affects endocrine, immune function and odor attractiveness of male offspring

We studied the effect of intrauterine food restriction (FR) on the immune function, endocrine status and attractiveness of scents of male rat-like hamsters, Cricetulus triton. Work was conducted on field-caught parents from the North China plain and their laboratory-born progeny. Restricted pregnant dams were fed 70% of the mean daily intake of hamsters with free access to food. FR caused a marked and protracted weight reduction of the body, adrenal, testes and epididymides in males. During the refeeding period, the spleen and thymus, but not the adrenal weight of the malnourished offspring caught up with that of the control after about 60 days. The present results demonstrated that estrous females preferred the odors of control males to that of FR males. Males whose mothers were food restricted during gestation had lower testosterone concentrations, immune responses and reproductive organ mass but had higher circulating cortisol than did the males in the control group. Thus, the effect of maternal FR may be an important cause in population regulation in the rat-like hamster. The testosterone level was positively correlated with immune function in rat-like hamsters, but the lower immunity was not suppressed by higher level of testosterone, as previously suggested. We also found a negative relationship between cortisol and immune function in the rat-like hamster.

Seasonal changes in and effects of familiarity on agonistic behaviors of rat-like hamsters (Cricetulus triton)

The seasonal changes in agonistic behaviors and effects of familiarity on agonistic behaviors in wild-caught adult rat-like hamsters (Cricetulus triton) were observed in dyadic encounters in a neutral arena. The aggression of opposite- and same-sex encounters became higher or remained the same during the non-breeding season. This indicates that the hamsters were solitary during both seasons. Familiarity increased the aggression in male–male encounters and decreased the aggression in female–female encounters during both seasons. Familiarity also increased the aggression in female–male encounters during the non-breeding season and had no effect on the aggression in female–male encounters during the breeding season. These results may be related to the hamster’s social structure. The more agonistic acts both male and female hamsters had, the more frequently they marked using flank glands during both seasons. This implies that flank gland marking can be used to advertise status and can be assessed by opponents to reduce the agonistic costs.

Food restriction affects reproduction and survival of F1 and F2 offspring of Rat-like hamster (Cricetulus triton)

Food restriction in parent may have long-term consequence on the reproductive capabilities of the offspring, and these consequences may, in turn, play an important role in population regulation. In this paper, we systematically examined the effect of maternal food restriction on reproduction and survival of maternal individuals, and F1 and F2 offspring of Rat-like hamsters (Cricetulus triton). Food restriction to 75% of that eaten by ad libitum-fed hamsters (75% FR) did not affect the reproductive organs and hormone concentration of maternal females, but 50% FR significantly reduced the size of ovarian organ and estradiol concentration of maternal females. 75% FR significantly reduced the testosterone concentration of maternal males; 50% FR significantly reduced both the size of epididymides and concentration of testosterone of maternal males. 70% FR in maternal females significantly reduced the sizes of reproductive organs and hormone concentrations of both their male and female F1 offspring. FR maternal females also produced significantly more male than female F1 offspring. The sizes of reproductive organs or hormone concentration of F2 males of maternal FR continued to significantly decline, but no such effect was observed in F2 females. However, the number of F2 offspring per F1 female of FR maternal females at birth became significantly smaller and with significantly more males than females. Survival to weaning of F1 and F2 offspring of FR maternal females became significantly smaller during the period from birth to weaning. Thus, the effects of maternal food restriction could be an important mechanism to explain the prolonged low population density that is commonly observed after the population crash of this species.

Seasonal changes in chronic social interactions and physiological states in female rat-like hamsters (Tscheskia triton)

We examined the behavioral characteristics and physiological states related to solitary lifestyle and dominant-subordinate relationships in female rat-like hamsters (Tscheskia triton), formerly known as Cricetulus triton. Wild adult hamsters were captured and caged singly in the laboratory during the non-breeding and breeding seasons. The experimental hamsters were subjected to 5 min staged dyadic encounters every day for 28 consecutive days by pairing two unfamiliar and weight matched females in a neutral arena. Aggressive behavior, defense and flank marking were quantified everyday within the first week and once each week during the last 3 weeks. Animals were then autopsied and their physiological and reproductive state assessed. Our results suggested that dominant-subordinate relationships could be established especially in non-breeding conditions, where the dominant displayed higher aggression and flank marking, and lower defense than its opponent. The breeding females followed this pattern except there was no difference in aggressive behavior, between the partners. The repeated encounters did not appear to reduce aggression or lead to amiable behavior or bonding. At the end of the experiment breeding females exhibited higher levels of serum estradiol, progesterone and corticosterone than non-breeding females. Both dominant and subordinate females in non-breeding condition had atrophied ovaries and uteri, whereas both dominant and subordinate females in breeding condition had hypertrophied ovaries and uteri. Non-breeding females possessed heavier and thicker flank glands than breeding females did. Dominant females displayed longer or thicker flank glands than subordinate did. Thus, our data suggest that the behavioral traits observed in our experiment support the solitary lifestyle of adult female rat-like hamsters and physiological state show some differences between social ranks or in both seasons.

Fecal hormone variation during prolonged social interaction in male Tscheskia triton

Agonistic behavior is crucial for conspecific members to maintain a social hierarchy, optimum population density, and high fitness. It is known that agonistic behavior and social ranking often interact with hormones such as testosterone (T) and glucocorticoids (GCs). The challenge hypothesis states that T levels in males are promoted by the agonistic behaviors of other males and has been widely testified in many taxa of vertebrates, even in humans, but seldom attempted in rodents. Here, we examined how fecal T and corticosterone (CORT) concentrations changed during prolonged social conflict in male greater long-tailed hamsters (Tscheskia triton). Dyads were subjected to 5 min staged encounters daily for 15 days during which agonistic and social behaviors were recorded and fecal hormone concentrations were determined by radioimmunoassay. Our results showed that pairwise male hamsters developed overt and stable dominant-subordinate relationships rapidly and that the agonistic behavior decreased over the course of the experiment. Dominant males exhibited more frequent flank marking and locomotion and shorter latency to initial attack than their subordinate counterparts. Testosterone levels were significantly increased in both dominant and subordinate males during early encounters, but T and CORT levels were higher in subordinate males. After five encounters, we found no difference between hormone levels and behavior for all males, implying some kind of behavioral and physiological habituation. This complex pattern of hormonal change during social conflict is discussed and correlations between behavioral and physiological habituation are hypothesized.

Effects of social conditions on adult and subadult female rat-like hamsters (Cricetulus triton)

As a solitary species, rat-like hamsters (Cricetulus triton) still live in family groups before they become mature and leave their families for a solitary life. This study aimed to investigate by a laboratory experiment if housing conditions have a different effect on physiological aspects of immature and mature females. We found that paired caged adult females became significantly heavier than their original weights; whereas the singly caged did not show significant change in their body weight. Although the subadults’ body weights increased significantly compared to their initial weights in both paired or singly caged groups, significant changes in body weight did not occur between the two groups. Although spleen and adrenal gland sizes were not significantly different between the two adult groups, the cortisol levels were significantly elevated by paired caging. In subadults, the adrenal size of the singly caged group was larger than that in the paired caged group despite there being no significant difference in cortisol level. Flank glands became significantly larger in paired caged adults than in singly caged adults, and there were no significant differences in subadults between the two groups. Additionally, ovaries and uteri of the paired caged adult females were comparatively lighter than those of the singly caged group; in contrast, ovaries and uteri of the paired caged group were larger than those of the singly caged group in subadults, although progesterone and estradiol levels did not show significant differences between the two adult groups. These different changes in physiological traits caused by housing conditions indicated that paired caging depressed adults and facilitated subadults; isolation facilitated adults and depressed subadults.

Effect of testosterone and melatonin on social dominance and agonistic behavior in male Tscheskia triton

Social dominance and agonistic behavior play important roles in animal societies. Melatonin and testosterone are closely related to social dominance and agonistic behavior in rodents, but interactions between both of them remain unknown. In this study we investigated the effects of testosterone and melatonin by manipulating photoperiod and castration on social dominance and agonistic behavior in male Tscheskia triton. Castration significantly decreases social dominance of both short- and long-day males, suggesting that testosterone benefits social dominance of males in both breeding and non-breeding seasons. In intact conditions, long-day males tended to dominate short-day males, suggesting that the effect of testosterone on social dominance was a little stronger than melatonin. However, castrated short-day males became dominant over their castrated long-day opponents meaning that high melatonin levels obviously benefit social dominance in males. Hormone implantation indicated that testosterone had no effect on non-breeding condition, but that melatonin was important during the breeding season. Our results indicate that both testosterone and melatonin are important in determining social dominance in male hamsters, and the effect of testosterone appears to be stronger than melatonin. Testosterone is responsible for aggression and social dominance in male hamsters during the breeding season, while melatonin regulates behavior during non-breeding, probably due to the different seasonal secretory patterns of the hormones.

Males’ Olfactory Discrimination of Receptive State of Females in Rat-Like Hamsters (Cricetulus Triton)

The odors of female mammals varies with reproductive states. Males can thus detect a female’s receptive status by the odors from the whole body odor, urine, specialized skin glands, or vaginal discharge. Generally, the odors of estrous females are more attractive to males than are the odors of diestrous females (Johnston, 1983; 1985; Lai et al., 1996; Ordinola et al., 1997). In many species, estradiol plays a role in regulating the attractiveness to males of some odor sources (Ferkin and Johnston, 1993; Ferkin et al., 1991).