Tscherskia Research Articles

Plagiorchis muris infection in Apodemus agrarius from northern Gyeonggi-do (Province) near the demilitarized zone

The small intestines of 6 species of rodents and 1 species of insectivore were examined seasonally for Plagiorchis muris infection in 3 different localities in northern Gyeonggi-do (Province), near the demilitarized zone (DMZ). A total of 1,496 animals, including 1,366 Apodemus agrarius, 54 Crocidura lasiura (insectivore), 32 Mus musculus, 28 Micronytus fortis, 9 Eothenomys regulus, 6 Micronys minutus, and 3 Cricetulus triton, were live-trapped at Yeoncheon-gun (n = 351), Paju-shi (804) and Pocheon-gun (343) at 3-mo intervals from December 2004 to September 2005. A total of 1,647 P. muris were collected from 72 (5.3%) A. agrarius. The infection rate was the highest in Pocheon-gun (8.2%), followed by Yeoncheon-gun (5.0%) and Paju-shi (4.2%). A higher infection rate was observed in A. agrarius captured during September (19.4%) than those captured during December (3.0%), June (2.6%), or April (0%). However, the worm burden was the highest in June (av. 32.1/animal), followed by September (24.7), December (4.0), and April (0). None of the other animal species were found infected with P. muris. The results reveal that A. agrarius is a natural definitive host for P. muris, and infection rates and worm burdens vary seasonally and geographically.

The highly polymorphic microsatellite markers for the greater long‐tailed hamster (Tscherskia triton)

AbstractWe isolated 25 dinucleotide microsatellite loci from the greater long‐tailed hamster (Tscherskia triton) populations in North China. We developed the amplification conditions of polymerase chain reaction for producing high‐resolution genetic markers for each locus. We found 10 microsatellite loci were highly polymorphic in 90 individual hamsters from three areas of North China, and the number of alleles in each locus varied from three to 11. These markers are potential tools for studying the genetic variation of the natural populations of this species.

Genetic diversity decreases as population density declines: Implications of temporal variation in mitochondrial haplotype frequencies in a natural population of Tscherskia triton

Although the spatial genetic differentiation that occurs in animal populations has been extensively studied, information on temporal variations in genetic structure and diversity is still lacking, especially for animals with oscillating populations. In the present study, we used the mtDNA D-loop sequence to assess the temporal genetic variation in samples from six successive years for the greater long-tailed hamster, Tscherskia triton. Sampling was carried out between 1998 and 2003 in cropland on the North China Plain, China. A total of 108 individuals were analyzed. The temporal samples showed a high level of genetic diversity. Substantial genetic changes in haplotype frequencies over time were detected for the hamster population. Random genetic drift and migration are likely to be the major factors responsible for the observed temporal pattern. The genetic diversity of the hamster population was higher in years with higher population density, and lower in years with lower population density. The result supports our hypothesis that genetic diversity decreases when population density declines in animals whose population oscillates greatly between years. The combined effects of inbreeding and genetic drift caused by reproduction, dispersal and population size might play important roles in the observed changes in genetic structure and diversity between years.

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.

Species differences among various rodents in the conversion of 7α-hydroxycholesterol in liver microsomes

Our previous study demonstrated that there are species differences among vertebrates in their conversion of 7α-hydroxycholesterol (7HC) to 7-ketocholesterol (7KC). To examine this further, we investigated the differences in the products of 7α-hydroxycholesterol in various species of male muroid rodents. Adult male Syrian hamsters ( Mesocricetus auratus), dwarf hamsters ( Phodopus rovolovskii), Djungarian hamsters ( Phodopus sungorus), Chinese hamsters ( Cricetulus griseus), rat-like hamsters ( Tscherskia triton), and hispid cotton rats ( Sigmodon hispidus) were used. Microsomal fractions were prepared from their livers, and the activities of the enzymes that participate in the dehydrogenation of 7α-hydroxycholesterol were determined by measuring the products using high-performance liquid chromatography. 7α-hydroxycholesterol was converted to both 7α-hydroxy-4-cholesten-3-one (7HCO) and 7-ketocholesterol in all of the hamsters tested. However, in the rat-like hamster and the hispid cotton rat, 7α-hydroxycholesterol was converted mostly to 7α-hydroxy-4-cholesten-3-one, as also observed in the rat ( Rattus norvegicus). The results suggest that microsomal enzyme activity in the conversion of 7α-hydroxycholesterol to 7-ketocholesterol varies considerably, even within the subfamily Cricetinae and the family Muridae.

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.

MITOCHONDRIAL DNA PHYLOGEOGRAPHY OF POPULATIONS OF CRICETULUS TRITON IN THE NORTH CHINA PLAIN

The greater long-tailed hamster (Cricetulus triton) is widely distributed in the farmlands of northern China. By using DNA sequence data from the mitochondrial D-loop region, we examined genetic diversity and genetic differentiation of 3 mountain populations of the greater long-tailed hamsters in 2 river drainages and 4 plain populations in the North China Plain. Phylogenetic analyses with parsimony and Bayesian inference, nested clade analysis, and analysis of molecular variance were used. The results showed that each population was significantly differentiated from others and the species possessed a high level of phylogeographic structure. The haplotypes were grouped into 2 clades that corresponded to 2 distinct topographic ranges: the mountain and the plain region. The split between the 2 clades accounted for 24% of the genetic variance observed among the examined samples. This study indicated that contiguous mountains played a potential role in genetic differentiation of the greater long-tailed hamsters in the North China Plain. It is suggested that limited gene flow among mountain populations or between mountain and plain populations, plus the impact of inbreeding or genetic drift on the small and isolated populations, accelerated genetic differentiation of mountain populations from plain populations of the greater long-tailed hamsters.

Sex-biased dispersal of greater long-tailed hamster (Tscherskia triton) revealed by microsatellites

For 2 consecutive years we studied the effect of dispersal on the genetic diversity of greater long-tailed hamsters (Tscherskia triton (de Winton, 1899)) in farmland habitat, Hebei Province, People's Republic of China. Level of genetic diversity was estimated by analyzing six highly polymorphic microsatellite loci in terms of mean d2, allele number, allelic diversity, effective number of alleles, allelic richness, average observed heterozygosity, and expected heterozygosity. The genetic diversity in populations from both two sites and 2 years indicated that the males contained higher levels of genetic diversity than the females, which supported our prediction that male-biased dispersal increased population genetic diversity. We also found significant departures from Hardy–Weinberg equilibrium and a reduction in genetic diversity in samples from a partially isolated site, which was probably due to genetic drift, inbreeding, or a combination of these factors.

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.

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.

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.

Molecular epidemiological study for tick-borne disease (Ehrlichia and Anaplasma spp.) surveillance at selected U.S. military training sites/installations in Korea.

Vector-borne diseases are a potential public health threat to U.S. Forces Korea (USFK). Ehrlichia and Anaplasma spp., transmitted by ticks, are only two of several diseases that may affect military readiness and operations. Rodents were collected at selected U.S. military installations and training sites in the Republic of Korea. DNA was extracted from spleen tissues and assayed by PCR methods for Ehrlichia and Anaplasma species. From rodents and mustelids collected during 1999 and 2000, a total of 196 Apodemus agrarius (striped field mouse), 2 Mustela sibirica (weasel), and 1 Cricetulus triton nestor (Korean greater long-tailed hamster) were assayed for Ehrlichia and Anaplasma species-specific DNA fragments. Rodent surveillance indicated a very high prevalence of Ehrlichia and Anaplasma spp. at selected training sites. Ehrlichia/Anaplasma DNA were identified from spleen tissue from 157 Apodemus agrarius, 1 Mustela sibirica, and 1 Cricetulus riton nestor. Species-specific DNA fragments of E. canis (45), E. ewingii (16), A. phagocytophila (5), and A. platys (62) were amplified by PCR techniques. Seventy-one striped field mice had single infections, while 24 had mixed infections of 2 (17 specimens), 3 (7 specimens), or 4 (1 specimen) pathogens. The striped field mouse plays a role as a reservoir for latent infections of various Ehrlichia or Anaplasma species.

Experimental fascioliasis in the rat-like hamster, Tscherskia triton, and other rodent hosts

Experimental infection with Fasciola hepatica and parthenogenetic Fasciola sp. in laboratory animals have been conducted in rats and rabbits. Inoculation of less than 5 metacercariae into rat-like hamsters, Tscherskia triton, is sufficient to establish Fasciola infections. The prepatent period of F. hepatica and the parthenogenetic Fasciola sp. in T. triton was shorter than that in rats and rabbits, suggesting that T. triton is a suitable experimental model for these flukes. In contrast, F. gigantica infection in T. triton did not yield adult flukes; T. triton, is therefore, considered to be an unsuitable host for F. gigantica. The cotton rat, Sigmodon hispidus, was an unsuitable host for the parthenogenetic Fasciola sp.

The rat-like hamster, Tscherskia triton, as a host for the parthenogenetic liver fluke Fasciola sp.

Metacercariae of parthenogenetic Fasciola sp. triploid were inoculated into the rat-like hamster Tscherskia triton. Flukes at various stages of growth were found in the bile ducts of all 8 (50%) animals that survived from 42 to 90 days. The body length to width ratio ranged from 1.8 to 2.9, and flukes with the highest ratio were passed 68 days after inoculation. Our results indicate that T. triton is a suitable host for experimental infection when induced by a small number of metacercariae (less than 5) of Fasciola sp.

The Rat-like Hamster, Tscherskia triton, as a Host for the Parthenogenetic Liver Fluke Fasciola sp.

The Rat-like Hamster, Tscherskia triton, as a Host for the Parthenogenetic Liver Fluke Fasciola sp.

Scent, social status, and reproductive condition in rat-like hamsters ( Cricetulus triton)

This study investigated the interrelations among scent glands, social status, and reproductive conditions in male rat-like hamsters ( Cricetulus triton), along with differential attraction of estrous females to conspecific males with different social status and reproductive condition. First, there were positive correlations between testes weights and flank glands and midventral glands. Second, castrated males were dominated by both intact males and castrated males treated with testosterone. Third, estrous females were less attracted to the scents from flank glands and midventral glands of castrated males. Moreover, dominant males had heavier testes and higher levels of circulating testosterone, and estrous females were more attracted to dominant males' scents. Our results indicated that estrous females were able to discriminate between the odors of two strange males with differences in reproductive conditions or social status.

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.

P21 オオキヌゲネズミ Tscherskia triton の肝蛭感受性

P21 オオキヌゲネズミ Tscherskia triton の肝蛭感受性

Effects of Photoperiod and Ambient Temperature on the Gonadotropin-Releasing Hormone Neuronal System in the Gray Hamster, Tscherskia triton

In seasonal breeders like the hamster, gonadal function depends on the photoperiod. The present study examined the effects of different photoperiods and ambient temperatures on the gonadotropin-releasing hormone (GnRH) neuronal system in male gray hamsters, Tscherskia triton. Hamsters were kept from birth under a long-day (LD: 16 h light and 8 h dark) photoperiod and at 23°C until the experiment began. The animals were then kept for 30 days under different photoperiods and ambient temperatures. After autopsy, immunocytochemical and semiquantitative reverse transcription-polymerase chain reaction analyses were performed on the hamster forebrain. Exposure to a short-day (SD: 8 h light and 16 h dark) photoperiod at 23°C induced a functional decline in the GnRH neuronal system (increased neuron number and immunoreactivity, and reduced cell size). LD with low ambient temperature (7°C) did not influence the GnRH neuronal system. In contrast, SD with low ambient temperature enhanced the SD-induced functional decline in GnRH neurons. Changes in immunoreactivity of GnRH fibers in the median eminence, their release site, were also similar to those in neuronal perikarya. Significant differences in GnRH gene expression were detected in the SD only group and the SD with low ambient temperature group. However, no differences were detected between the two groups. These findings suggest that low ambient temperature enhanced the SD-induced decline in GnRH release from nerve terminals, but was not a crucial factor in the synthesis of this decapeptide.

Epidemiological study of autumn-winter type scrub typhus in a new endemic focus of Fei County, Shandong Province, China

To characterize the epidemiology of autumn-winter type scrub typhus in a new endemic focus of Fei County, Shandong Province, China, field and laboratory studies were conducted to determine the species composition and seasonal fluctuations of chigger mites and their animal hosts. Orientia tsutsugamushi was isolated, and serotypes of antibodies to O. tsutsugamushi were detected and identified. A total of 1044 rodents and insectivores were field collected: 751 Apodemus agrarius (71.94%), 266 Tscherskia triton (25.48%), 1 Cricetulus barabensis (0.09%), 11 Rattus norvegicus (1.05%), 3 Mus musculus (0.29%), and 12 Crocidura suaveolens (1.15%). Apodemus agrarius, T. triton and R. norvegicus were shown to be naturally infected with O. tsutsugamushi. The serum antibody positive rate of rodents was 14.78%. A total of 11762 chigger mites were collected: 2547 Leptotrombidium scutellare (21.65%), 1596 L. palpale (13.57%), 466 L. taishanicum (3.96%), 2833 L. linhuaikongense (24.09%), and 4320 Walchia pacifica (36.73%). Leptotrombidium scutellare was most numerous from September to November and was the predominant species during the local scrub typhus epidemic season. Natural infection with O. tsutsugamushi was detected in L. scutellare, and transovarial transmission of the pathogen by this chigger was demonstrated. 38 strains of O. tsutsugamushi were isolated from 33 patients (14 strains), 3 species of rodents (9 strains), and 4 species of mites (15 strains). All O. tsutsugamushi strains isolated in this endemic focus were of low virulence. Serotype identification showed that 33 strains were of the Gilliam type, and 3 strains were of the Karp type. Another 2 strains remain to be identified. In the Fei County focus of scrub typhus, the main reservoir host is A. agrarius, the predominant mite vector is L. scutellare, the principal serotype of O. tsutsugamushi is Gilliam, and all strains of O. tsutsugamushi areof low virulence. Most cases of scrub typhus occurred from September to November; therefore, scrub typhus in this focus is autumn-winter type. This focus is located in the premontane flatlands of Fei County.