Factors influencing range contraction of a rodent herbivore in a steppe grassland over the past decades.

Climate warming and human disturbance are known to be key drivers in causing range contraction of many species, but quantitative assessment on their distinctive and interactive effects on local disappearance is still rare.In this study, we examined the association of climate warming and human disturbance stressors with local disappearance probability of Brandt's voles (Lasiopodomys brandtii) in a steppe grassland in northern China.We used logistic generalized additive models to quantify the relationship between local disappearance probability of Brandt's voles and environmental variables. The year following the last observation year was used to estimate the disappearance threshold of Brandt's voles. We projected the distribution change of Brandt's voles under future climate warming scenarios.We found climate warming attributed to local disappearance and range contraction for southern populations of Brandt's voles from 1971 to 2020. Human stressors and high vegetation coverage increased the probability of local disappearance of voles in years of abundant precipitation. The southern boundary retreated northward at a speed of 99.0 km per decade with the temperature rise of 0.36°C. The disappearance threshold of maximum air temperature of Brandt's voles in the warmest month (27.50 ± 1.61°C) was similar to the lower critical temperature of its thermal neutral zone.Our study suggests that the rapid climate change over the past decades contributed to the range contraction of its southern boundary of this keystone species in the steppe grassland of China. It is necessary to take actions to preserve the isolated populations of Brandt's voles from the effects of accelerated climate change and human disturbance.

The colonization and divergence patterns of Brandt's vole (Lasiopodomys brandtii) populations reveal evidence of genetic surfing.

BACKGROUND: The colonial habit of Brandt's vole (Lasiopodomys brandtii) differs from that of most other species of the genus Microtus. The demographic history of this species and the patterns shaping its current genetic structure remain unknown. Here, we explored patterns of genetic differentiation and infered the demographic history of Brandt's vole populations through analyses of nuclear microsatellite and D-loop sequences. RESULTS: Phylogenetic analyses divided the sampled populations into three main clusters, which represent the southeastern, northeastern and western parts of the total range in Mongolia and China. Molecular data revealed an ancestral area located in the southeast of the extant range, in the Xilinguole District, Inner Mongolia, China, from where Brandt's vole populations began expanding. A gene flow analysis suggested that the most likely colonization route was from the ancestral area and was followed by subsequent northeastward and westward range expansions. We identified decreases in genetic diversity with increasing distance from the founder population within the newly occupied regions (northeastern and western regions), clinal patterns in the allele frequencies, alleles that were rare in the original area that have become common in the newly occupied regions, and higher genetic differentiation in the expanded range compared with the original one. CONCLUSION: Our results indicate that L. brandtii most likely originated from the southeastern part of its current geographic range, and subsequently colonized into the northeastern and western parts by expansion. The genetic patterns among the derived populations and with respect to the original population are consistent with that expected under genetic surfing models, which indicated that genetic drift, rather than gene flow, is the predominant factor underlying the genetic structure of expanding Brandt's vole populations.

Effects of levonorgestrel-quinestrol (EP-1) treatment on Mongolian gerbil wild populations: a case study.

Rodent pest population outbreaks occur frequently in grassland ecosystems in northern China. The Mongolian gerbil (Meriones unguiculatus) is a dominant pest rodent which is distributed across the semi-desert grasslands of Inner Mongolia, China. In 2009, we studied the contraceptive effect of levonorgestrel-quinestrol (EP-1), concentration 50 ppm, on a wild Mongolian gerbil population. The one-off contraceptive treatment was compared with a control group using a semi-monthly live trapping method in the Ordos Semi-desert Grassland Region of Inner Mongolia. The results show that juveniles were not recruited in spring in the treatment group. Ratios of juveniles in the control and treatment groups showed significant semi-monthly differences from spring to summer (one-way ANOVA, F2, 14 = 7.53, P < 0.05). Between both groups, annual fluctuations of juvenile and total population densities were significantly different respectively (F2, 14 = 4.64, P < 0.05; F2, 18 = 7.72, P < 0.05). The contraceptive EP-1 delayed the normal reproductive pattern of Mongolian gerbil populations. This suppressed birth rates of gerbil populations, reduced their densities, and changed their age structures. The period of EP-1 baiting should be extended but it could be an ideal method for controlling Mongolian gerbil populations during each breeding season.

Fertility control of Rattus nitidus using quinestrol: effects on reproductive organs and social behavior.

Fertility control has been identified by studies in the laboratory and the field as a more appropriate and long-term control strategy for rodent pests than lethal control. In this study, we investigated the effects of quinestrol on mass of reproductive organs and on social behaviors in female and male Indochinese forest rat (Rattus andamanensis (Blyth, 1860)] using approach of morphometrics and genetics). [corrected]. A total of 16 adult females and 16 adult males were randomly assigned to 4 groups. One male and one female group were fed rice with 0.005% quinestrol by weight for 7 days, and another 2 groups were fed rice only. After 7 days, rats were assigned to 10 min dyadic encounters between groups, and investigation, aggression, defense and attack latency were quantified. All animals were killed on day 10, and reproductive organs were dissected and weighed. Dyadic encounter data showed that there were obvious changes in social behaviors of quinestrol-treated rats. Quinestrol significantly inhibited the investigative behavior of quinestrol-treated males toward control females in Rattus nitidus, but seldom affected investigation between control males and quinestrol-treated females. Aggression of control females toward quinestrol-treated males was higher than that of quinestrol-treated females, and defense of quinestrol-treated males toward control females was more remarkable than that of control males. Quinestrol remarkably decreased wet masses of epididymis and spermotophore in males and ovaries in females, but had no effect on wet masses of testes and uteri after quinestrol treatment. These results indicate that the anti-fertility effects of quinestrol on R. nitidus are attributed to not only suppressing reproductive organs but also impacting social behaviors associated with territory defense and mate choice.

Effects of quinestrol and levonorgestrel on prolactin serum concentration in lactating Mongolian gerbils (Meriones unguiculatus) and reproductive parameters of their offspring.

The effects of the two sterilants, quinestrol (QE) and levonorgestrel (LNG) on serum prolactin (PRL) level in lactating Mongolian gerbils and reproductive parameters of their offspring were examined in the study. Both sterilants increased the serum PRL level in lactating gerbils. The body weight as well as weights of the ovary, testis, epididymides, and seminal vesicles were lower, whereas that of the uterus was higher in the pups originating from QE-treated mothers in comparison to controls. Histological ovarian sections of the offspring from QE-treated mothers contained only growing follicles, whereas their uterine sections showed a thinner endometrium, thicker myometrium, and greater epithelial-cell height than in controls. The histometrical testis characteristics as well as sperm concentration and motility of male pups from QE-treated mothers were lower compared to those of the control group. The serum gonadotropin levels of female pups from mothers treated with QE were lower, whereas the serum estradiol (E(2)) and progesterone (P(4)) levels were higher than in control gerbils. In contrast, serum gonadotropin and testosterone (T) levels of male pups from QE-treated mothers were lower compared to controls. LNG did not affect the examined parameters of the offspring. The offspring from QE-treated mothers was infertile, whereas the offspring from LNG-treated mothers was fertile. In summary, QE and LNG have a stimulatory effect on PRL level in lactating gerbils. It also appears that QE administered via milk to mothers affects reproductive processes of their offspring.

Combined effects of levonorgestrel and quinestrol on reproductive hormone levels and receptor expression in females of the Mongolian gerbil (Meriones unguiculatus).

The effects of treatment with a combination of levonorgestrel and quinestrol (EP-1; ratio of 2:1) on reproductive hormone levels and the expression of their receptors in female Mongolian gerbils were examined. We show that serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH) decreased, whereas serum estradiol (E2) and progesterone (P4) increased after EP-1 treatment. EP1 down-regulated mRNA expression of the follicle-stimulating hormone receptor (FSHR) and the estrogen receptor (ER) ßin the ovary. EP-1 up-regulated the mRNA expression of the luteinizing hormone receptor (LHR) and the progesterone receptor (PR) in the ovary as well as ERα and PR in the uterus of Mongolian gerbils. The effects were time-dependent and dose-dependent. EP-1 had no obvious effects on ERα mRNA expression in the ovary. The current study demonstrates that the effect of EP-1 on the expression of ER subtypes is tissue-specific in Mongolian gerbils. EP-1 disrupted the reproductive endocrinology of the Mongolian gerbil. These findings suggest that the effects of EP-1 on reproductive hormone levels and their receptor expression in Mongolian gerbils may be the result of synergistic actions of levonorgestrel and quinestrol, with quinestrol playing the major role.

Re-feeding evokes reproductive overcompensation of food-restricted Brandt's voles.

In natural conditions, animals have to cope with fluctuations of food resources. Animals having experienced prolonged decrease in feeding opportunities may increase their reproductive success when meeting abundant food. Though food restriction is well known to reduce reproductive success of animals, it is not clear whether re-feeding can restore or even overcompensate the reproductive success. In this study, we investigated the differences in reproductive parameters between food-restricted and refed (FR-RF) group and control group of Brandt's vole (Lasiopodomys brandtii). For 4 weeks, FR-RF voles were provided with 70% of their normal daily food intake and then they were fed ad libitum for the next 4 weeks. Voles of control group were fed ad libitum for 8 weeks. Females (FR-RF or control) were mated to non-littermate males of the same group (FR-RF or control), and we found that the mean litter size and survival rate of F1 pups of FR-RF group were significantly higher than those of control group. We also provided a field example showing that the litter size of Brandt's voles tended to be higher if they experienced two consecutive dry and wet months than that of voles didn't have this experience. Our results suggest that re-feeding may have evoked an overcompensatory mechanism of food-restricted voles in reproductive success. This may be an adaptive strategy for Brandt's voles (with oscillating populations) to cope with the fluctuating food resources in natural conditions by adjusting their reproductive success.

Inhibitive effects of quinestrol on male testes in Mongolian gerbils (Meriones unguiculatus).

The current study evaluated effects of quinestrol on oxidative stress and abnormal spermatogenesis for male Mongolian gerbils. Gerbils were randomly divided into multi-dose treated, single-dose treated, control groups. At 15 days after treatment antioxidant enzymes (SOD, GSH-Px) activities and T-AOC were decreased whereas the MDA concentration was significantly increased, testicular weight and seminiferous tubular areas decreased, germ cells were rarefied and showed irregular distribution in seminiferous tubules, apoptosis was pronounced among spermatocytes and spermatids, the number of dead and abnormal acrosomes of spermatozoa increased significantly in quinestrol treated groups. At 30 days following treatment the testicular histopathological changes were more severe, sperm quality and antioxidant capacity continued to decline, and multi-dose treatment produced more damage to gerbils testes compared with single-dose treatment. The physiological indicators were recovered by 60 days of treatment withdrawal. The results showed oxidative stress induced by quinestrol in relation to abnormal spermatogenesis.

Quinestrol treatment induced testicular damage via oxidative stress in male Mongolian gerbils (Meriones unguiculatus).

The hypothesis that quinestrol exerts testicular damage via oxidative stress was investigated in male gerbils using a daily oral gavage of 3.5 mg/kg body weight for 2 weeks (the multidose-treated group) or 35 mg/kg body weight (the single-dose-treated group). The testicular histological morphology, antioxidant capacity and malondialdehyde (MDA) concentration in testicular tissue and plasma were assessed at 15, 30, and 60 days following treatment. The results showed that the activity of the antioxidant enzymes, including superoxide dismutase (SOD) and glutathione peroxide (GSH-Px), and total antioxidant capacity (T-AOC), at 15 days after treatment in testicular tissue decreased, which led to the MDA concentration increasing while at the same time germ cells were rarefied and showed an irregular distribution in seminiferous tubules of quinestrol-treated gerbils. At 30 days, the testicular weight and antioxidant capacity continued to decrease, while the MDA concentration continued to increase, and testicular histopathological changes were more pronounced. Single-dose and multidose drug treatment had a similar effect on the antioxidant enzymes and MDA, but testicular damage was relatively severe at 15 and 30 days after multidose treatment. By 60 days of treatment withdrawal, however, the above parameters recovered to control levels. The results show that quinestrol causes reversible damage to gerbil testes that might be caused by the oxidative stress and that multidose treatment has more effects on testicular damage compared with one-dose treatment.

Effects of quinestrol as a contraceptive in mongolian gerbils (Meriones unguiculatus).

The contraceptive effects of quinestrol in Mongolian gerbils were examined. The results showed that body weight significantly increased after quinestrol treatment, except in the group that received the highest dose. The gonadosomatic index of ovaries decreased, whereas that of uteri increased, and uterine edema appeared after quinestrol treatment. Histological examination revealed that the ovaries had a lack of mature follicles and corpora lutea and that the myometrium and endometrium of the uteri became thin after quinestrol treatment. Persistent estrous appeared after quinestrol treatment, and time to persistent estrous shortened with increasing doses of quinestrol. Serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels decreased, whereas estradiol (E2) and progesterone (P4) levels increased after quinestrol treatment, and the effects were dose-dependent. During gestation, the serum E2 levels in the different treatment groups were not significantly different. During gestation in the control groups, the serum P4 levels from days 0 to 15 were higher than in the quinestrol-treated groups; however, they did not show significant differences from days 18 to 24. Doses of 0.1 to 2.7 µg/g quinestrol over 6 days completely inhibited fertility. Birth time was prolonged with increasing doses of quinestrol. The findings suggest that quinestrol has marked estrogenic effects in Mongolian gerbils and may inhibit follicle maturation and ovulation through lowered gonadotropin levels. Uterine edema and abnormal E2 and P4 levels during gestation are important causes of pregnancy failure in quinestrol-treated Mongolian gerbils. Quinestrol causes prolonged inhibition of fertility in Mongolian gerbils.

Effects of levonorgestrel on reproductive hormone levels and their receptor expression in Mongolian gerbils (Meriones unguiculatus).

The effects of levonorgestrel (LNG) on serum levels of reproductive hormones and their receptor mRNA expression in the ovary and uterus of Mongolian gerbils were examined. The results show that serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH) increased, whereas serum estradiol (E2) and progesterone (P4) decreased profoundly after LNG treatment. LNG down-regulated the mRNA expression of follicle-stimulating hormone receptor (FSHR), luteinizing hormone receptor (LHR), estrogen receptor (ER) ß and progesterone receptor (PR) in the ovary, and ERα and PR in the uterus of Mongolian gerbils. The down-regulated effects were time-dependent and dose-dependent. LNG had no obvious effects on ERα mRNA expression in the ovary. The findings suggest that LNG impairs reproductive hormone receptor expression at the molecular level in Mongolian gerbils. Also, the two ER subtypes may play different roles in the ovary, and ERß may not be the predominant ER subtype in the uterus of Mongolian gerbils. The ovary and uterus may be the important sites of action of LNG through its direct progesterone-like effects in Mongolian gerbils.

Variations in serum gonadotropin and prolactin levels during consecutive reproductive states in Mongolian gerbils (Meriones unguiculatus).

Serum follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin (PRL) levels were examined during consecutive reproductive states in Mongolian gerbils. The results indicate that FSH, LH, and PRL levels peak at proestrus, estrus, and diestrus, respectively. During early gestation in primiparous gerbils, gonadotropin levels were the lowest on day 6. This was followed by an increase in FSH and LH levels until days 18 and 15, respectively, with levels remaining constant until day 21. However, in multiparous gerbils, gonadotropin levels were the lowest on day 12 of gestation and were relatively stable between days 15 to 21. In both primiparous and multiparous gerbils, gonadotropin levels increased rapidly from day 21 of gestation to day 3 of lactation, and kept stable between 6-24 days of lactation. PRL peaked during early gestation on days 9 and 6 in the primiparous and multiparous gerbils, respectively, followed by a decline. PRL levels subsequently peaked again on day 21 before parturition. During lactation, PRL levels peaked on days 6 and 9 in primiparous and multiparous gerbils, respectively, followed by a decline until lactation ended. These findings suggest that variations in gonadotropin during the estrous cycle, gestation, and lactation in Mongolian gerbils are similar to those observed in rats, whereas prolactin levels differ. Changes in gonadotropin and prolactin levels during different reproductive states were found to be similar in primiparous and multiparous gerbils, and were correlated with the reproductive stages of Mongolian gerbils.

Adult exposure to sasanguasaponin induces spermatogenic cell apoptosis in vivo through increased oxidative stress in male mice.

Effects of sasanguasaponin (SGS), a compound from defatted seeds of Camellia oleifera, on abnormal spermatogenesis were studied in adult male mice using daily intragastric administration of 100, 200 and 400 mg/kg body weight (BW) for 6 weeks. The sperm counts decreased and the number of abnormal spermatozoa increased in mice treated with SGS at 400 mg/kg dose level. Testicular weight and seminiferous tubular area gradually decreased as dosage increased to 400 mg/kg SGS. Germ cells were rarefied and showed irregular distribution in seminiferous tubules (STs). Apoptosis was pronounced among spermatocytes and spermatids at the 400 mg/kg dose level. Antioxidant enzymes including superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and total antioxide capacity (T-AOC) markedly decreased and malondialdehyde (MDA) concentration increased in the testes. These results suggest that adult exposure to SGS (400 mg/kg) induces spermatogenic apoptosis through increased oxidative stress in male mice.

Development and validation of a HPLC method for determination of levonorgestrel and quinestrol in rat plasma.

Levonorgestrel and quinestrol, commonly known as EP-1, has long been used in the control of wild rodents. Up to the present time, however, no method for simultaneous quantification of levonorgestrel and quinestrol in rat plasma has been reported. In the present study, a sensitive reverse-phase high-performance liquid chromatography with ultraviolet detection (RP-HPLC-UV) method for quantification of levonorgestrel and quinestrol in rat plasma has been developed. It uses a Kromasil ODS C(18) column and acetonitrile-0.1% formic acid (85 : 15, v/v) mobile phase at ambient temperature. The plasma sample was prepared by hexane-isoamyl alcohol extraction (90 : 10, v/v). The flow rate and detection wavelength were 1.0 mL/min and 230 nm. The correlation coefficients were greater than 0.9995 within 0.08-50 microg/mL for levonorgestrel and 0.12-50 microg/mL for quinestrol, and the limits of detection were 0.02 and 0.05 microg/mL for levonorgestrel and quinestrol, respectively. Average recovery ranged from 92.5 to 96.3% and inter-day RSDs were less than 7.56%. This method can be applied to the further pharmacokinetic study of levonorgestrel and quinestrol in rat plasma.

Adult exposure to diethylstilbestrol induces spermatogenic cell apoptosis in vivo through increased oxidative stress in male hamster.

Effects of diethylstilbestrol (DES), an endocrine disrupting chemical, on abnormal spermatogenesis were studied in adult hamster using daily subcutaneous injection of 0.01, 0.1 and 1.0mg/kg body weight for 1 week. Testicular weight and seminiferous tubular area gradually decreased as dosage increased to 1.0mg/kg DES. Germ cells were rarefied and showed irregular distribution in seminiferous tubules. Apoptosis was pronounced among spermatocytes and spermatids at the 1.0mg/kg dose level. Antioxidant enzymes, including superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), and total antioxide capacity (T-AOC) markedly decreased and malondialdehyde (MDA) concentration significantly increased in the testes. These results suggest that DES (1.0mg/kg) induces testicular oxidative stress and spermatogenic apoptosis in adult male hamsters to extend findings shown for prenatal and/or neonatal exposure.

Infection of SARS-CoV on juvenile and adult Brandt's voleMicrotus brandtii.

We studied the infectious effect of SARS-CoV virus on juvenile and adult Brandt's Vole (Microtus brandtii) by nasal cavity spraying method (CCID50 is 105.7). SARS virus caused serious deaths in adults. The death adults demonstrated hemorrhage from mouth, nasal cavity and intestine, hemorrhageious interstitial pneumonia and gore in liver, spleen and kidney. The survival adults demonstrated local hemorrhagic spot in lung and emphysema, but the other organs showed no pathological abnormality. SARS virus caused no deaths in juveniles, but locomotion of infected juveniles became slower. In the early stage, there was local pneumonia in lung and SARS viruses were isolated from the pathological tissue. Only one control juvenile lived and the infected juvenile showed local pneumonia in lung. The results demonstrated that SARS-CoV infected Brandt's vole seriously and adults were more susceptive to SARS-CoV than juveniles. The Brandt's vole may be a potential animal model for SARS research.