The effects of the nematode parasite Skrjabingylus nasicola on British weasels (Mustela nivalis)

Adult worms of Skrjabingylus nasicola are found in the nasal sinuses of mustelids, and when numerous may cause considerable distortion of the frontal bones. A heavy infestation is commonly assumed to be detrimental to the individual and possibly also to the population. To examine this belief, the frequency of occurrence ("incidence") and extent of damage caused by S. nasicola were analysed with respect to the climate of seven sample areas and the age, sex and body size of 614 British weasels. Incidence ranged from 69–100% of the sample, and mean skull damage from 31 to 53 on an index scale of 0–8 points. Significant correlations were found between incidence and date of collection of young weasels, and between extent of damage and mean number of rain-days in the area. Male weasels were more badly damaged than females, though incidence was the same in both sexes. There was no evidence that badly damaged weasels were smaller, lighter, leaner or died sooner than lightly or undamaged ones, nor that, in the wild, they were infested by eating shrews.     

Body size of the weasel Mustela nivalis and the stoat M. erminea in Sweden

In this study we examined temporal and geographical variations in a sample of 124 skulls of the weasel Mustela nivalis and 146 skulls of the stoat M. erminea, collected in Sweden between 1959-1992 and 1913-1990, respectively.We used Principal Component Analysis (PCA) to combine the effects of latitude, longitude, year of collection, mean ambient temperature and Net Primary Productivity (NPP). The first principal component (PC1) contained latitude, ambient temperature and NPP and was significantly and positively related to male (but not female) skull size of both stoats and weasels. None of the other factors or their interactions were significantly related to skull size.We conclude that ambient temperature, either directly through energy savings, or indirectly through improved food availability (increased NPP), had a significant effect on determining body size of male stoats and weasels in Sweden. Our results support the hypothesis that male and female of these species are affected by different selection pressures and thus react differently to changing environmental conditions.     

The Jeju weasel, Mustela sibilica quelpartis, a new definitive host for Gnathostoma nipponicum Yamaguti, 1941

Adult gnathostomes were discovered in the stomach of the Jeju weasel, Mustela sibilica quelpartis, road-killed in Jeju-do (Province). Their morphological characters were examined to identify the species. Total 50 gnathostome adults were collected from 6 out of 10 weasels examined. In infected weasels, 4-6 worms were grouped and embedded in each granulomatous gastric tumor, except 1 weasel. Male worms were 25.0×1.4 mm in average size, and had a tail with pedunculate papillae, a spicule, and minute tegumental spines. Females were 40.0×2.5 mm in average size, and had a tail without tegumental spines. Pointed and posteriorly curved hooklets were arranged in 8-10 rows on the head bulb. Tegumental spines were distributed from behind the head bulb to the middle portion of the body. The spines were different in size and shape by the distribution level of the body surface. Fertilized eggs were 65.5×38.9 μm in average size, and had a mucoid plug at 1 pole. These gnathostomes from Jeju weasels were identified as Gnathostoma nipponicum Yamaguti, 1941. By the present study, it was confirmed for the first time that G. nipponicum is distributed in Jeju-do, the Republic of Korea, and the Jeju weasel, M. sibilica quelpartis, plays a crucial role for its definitive host.     

No evidence of past bottlenecks in two Danish mustelids: results of craniometric and genetic studies in time and space

A craniometric and molecular genetic investigation was conducted in Danish stoat (Mustela erminea) and weasel (Mustela nivalis) populations. Specimens used were collected over a wide time span (stoat: 1864–2002; weasel: 1863–1990) and from several geographical regions (Jutland peninsula and the two islands of Funen and Zealand). The study was made with a temporal and a spatial perspective, allowing the estimation of differences in genetic diversity and craniometrical trait means between geographical regions and through time with the use of ancient DNA techniques. Univariate statistics of 11 trait lengths did not reveal geographical differentiation in size and shape among the different regions for the stoat, but a geographical differentiation in shape was found for the weasel. There was evidence for reductions in skull size with the year of collection in male stoats, but not in females, which suggests that some selective pressures or environmental factors have affected male stoats to a greater extent than female stoats and the weasel. Relatively high values of heterozygosity were found in both the stoat and weasel, using microsatellite markers. The level of genetic variability of the stoat collected recently was compared with the level of genetic variability in the historical samples, demonstrating that the stoat has not suffered severe loss of genetic variability through the investigated period. A comparison of recent and historical genetic variability of the weasel was not possible because the ancient DNA extracted from the weasels was too degraded. Pairwise F_ST values and assignment tests showed small but significant genetic differentiation between the different geographical regions for both the stoat and weasel. No genetic differentiation between the recent and historical samples of the stoat was found. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 88 , 541–553.     

Movement patterns of a specialist predator,the weasel<Emphasis Type="Italic">Mustela nivalis</Emphasis> exploiting asynchronous cyclic field vole<Emphasis Type="Italic">Microtus agrestis</Emphasis> populations

We investigated habitat selection and movement characteristics of male weaselsMustela nivalis Linnaeus, 1766 during the breeding season through radio-telemetry in Kielder Forest (KF) in order to assess how weasel movement is influenced by prey dynamics, mate searching and predation risk, and whether the scale of weasel movement corresponds to the spatial scale of the asynchronous, multi-annual vole population cycles observed in KF. Weasels used habitats with a high proportion of grass cover to a much larger extend than habitats with less grass cover and moved through the latter habitats faster and / or straighter. Habitats with high amounts of grass cover also had the highest field vole abundance, although total rodent abundance did not differ between habitats. The selection of this habitat by weasels might reflect weasels preferring field voles as prey or avoiding habitats with little grass cover and high intraguild predation risk. Five out of 8 male weasels radio-tracked had low day-to-day site fidelity and moved between different clear cuts. Three other males were resident in a single clear cut. This variation may reflect mate searching by male weasels. The observation that most weasels (5 out of 8) roamed over large areas and the scale of their dispersal potential suggests, that if they regulated vole populations, they should have a greater synchronising effect on the spatial scale of vole population dynamics than what is observed in vole populations in KF.     

黄鼬在吉林环长白山旅游公路路域活动的调查研究

2008年11～12月,采用样线法对环长白山旅游公路改扩建工程全线路域200 m范围内黄鼬活动情况进行了3次调查.调查结果显示:K10～K45路段黄鼬穿越公路较多;黄鼬穿越公路频率与路域植被类型和雪被深度有密切的关系;黄鼬已经开始利用涵洞穿越公路;公路对黄鼬具有吸引效应,影响域范围约为50 m.为此提出了相应的保护对策.     

Neoplasia in the Siberian weasel (<Emphasis Type="Italic">Mustela sibirica</Emphasis>): two case reports of fibrosarcoma and interstitial cell tumour

Two cases of neoplasia occurred in two adult Siberian weasels (Mustela sibirica) in a game reserve in southern Lower Saxony, Germany. The first case, a male weasel, showed an enlargement of the right testicle, which was surgically removed. The tumour was classified as an interstitial cell tumour. One year after surgery, the male weasel died by accident and revealed tumour lesions of uncertain histogenesis within the abdominal cavity and the spleen at necropsy. The second case, a female animal, became suspicious by a dermal mass in the upper left hind limb, which was also surgically excised. Pathological examinations revealed a fibrosarcoma that recurred twice after removal of the original mass. These two cases of neoplasia in the Siberian weasel are demonstrated with regard to clinical aspects and discussed on the basis of their pathomorphological features.     

The influence of host sex on the L3 to L4 molt of Brugia malayi

Immunocompetent male mice are more susceptible to experimental infection with Brugia spp. than are females. Because permissive male SCID mice (severe combined immunodeficient mice), which lack T and B cells, also possess higher worm burdens, the mechanism is not solely immune mediated. Recovery of fewer adult worms from the female SCID mouse suggests that females do not provide sufficient nutrients for larval growth. This study assessed the potential of the female SCID mouse to support the L3 to L4 molt of Brugia malayi. Unexpectedly, worms grown in females molted at earlier time points of recovery than those harvested from males. This suggests that the early stage of development of B. malayi is delayed in the male murine host. To determine whether the effect of host sex on molting may be similar in humans, worms were cultured in media supplemented with serum from male or female donors. Worms grown in serum obtained from female donors exhibited a significantly higher percentage of complete molts over those cultured with serum from males. Host-derived molecules required for the L3 to L4 molt may be more abundant in the female, perhaps allowing the worms to survive a vulnerable developmental stage in a less permissive environment.     

香鼬的栖息地选择、觅食和育幼行为

香鼬（Ｍｕｓｔｅｌａａｌｔａｉｃａ）喜栖于人类居住区附近的高寒草甸草场,主要以高原鼠兔（Ｏｃｈｏｔｏｎａｃｕｒｚｏｎｉａｅ）为食,其数量分布与高原鼠兔的密度分布成正相关。在高原鼠兔的繁殖盛期,香鼬主要捕食鼠兔幼体,每只成体平均每天捕获鼠兔６．２只,相当于每１００克体重日获取食物重量２７３．５克,在高原鼠兔的繁殖后期和非繁殖期,每只成体平均每天捕获鼠兔２．７５只,相当于每１００克体重日获取食物重量２９６．３克。繁殖期育幼任务全部由雌性成鼬承担,幼鼬从７月初开始地面活动,８月初开始扩散。     

Population biology of the weasel Mustela nivalis on British game estates

The mean year-class ratio in 6 samples of weasels (total n = 477) ranged from 59% to 84% young, and mean age from 0.79 to 1.16 yr. There was no difference in age structure between samples from 5 game estates and 1 reserve. Mean annual mortality of weasels of both sexes and all ages was 75-90%. In 12 pregnant weasels the mean number of embryos, observed from April to June, was 5.6. There was a definite anoestrous season in winter. Records of the number of weasels killed on game estates show that weasels and stoats reacted differently to the first outbreak of myxomatosis in England in 1954; and that weasel populations are capable of enormous sudden increases (usually associated with "mouse years"). These increases are probably due largely to summer litters produced by precocious juveniles, and also to some adults breeding a second time (both possibilities confirmed from ovarian histology on this material). Traditional gamekeeping practice may influence the seasonal pattern of mortality of weasels (highest in spring) but its effects are probably short-lived.     

Reproductive development of female Schistosoma mansoni (Digenea: Schistosomatidae) following bisexual pairing of worms and worm segments

Maturation and maintenance of normal reproductive function in female Schistosoma mansoni require a permanent association with the male, but the nature of this relationship is not well understood. The regional localization of a stimulatory factor in the male and its target in the female were investigated. Unisexual female and mature male worms were transected into segments of various lengths. Various combinations of transected male and female segments and intact worms were transferred to the mesenteric veins of recipient hamsters and were also maintained in vitro. In hamsters and in vitro, pairing took place between intact worms of each sex and segments of the other, and between segments of both sexes. The majority of female worms and segments so paired showed some reproductive development, as assessed by vitelline gland differentiation. In intact unisexual females paired with small male segments, vitelline gland development was limited to that portion of the worm that had been held by the male. Worm segments continued to display normal body contractions throughout 24 days of in vitro maintenance and morphological integrity was retained. It is concluded that 1) in the absence of a functioning gut, worm segments can survive for prolonged periods on nutrients absorbed through the tegument; 2) worm pairing, male stimulation, and the female developmental response are independent of central nervous control by the cerebral ganglia; 3) males have no centralized localization for the female-stimulating factor; 4) vitelline gland differentiation in the female requires local stimulation through male contact, and this is not propagated throughout the worm.     

Density-dependent effects on the survival and growth of the rodent stomach worm Protospirura muricola in laboratory mice

The spirurid nematode, Protospirura muricola, is of intrinsic interest as a rodent model of gastric nematode infections. Since worm burdens can be very heavy in nature, density dependent processes may constrain parasite growth. Laboratory mice (BKW) were exposed to varying doses of infective larvae of P. muricola in the range 5 to 40 third-stage larvae (L3), in four separate experiments in which progressively higher doses were utilized. All mice were culled 60 days after infection and a total of 518 worms (226 male and 292 female worms) was recovered, measured and weighed. Overall survival was 58.9%, but survival declined significantly with increasing dose by approximately 21% (from 66% at 5 L3 per mouse to 52% at 40 L3 per mouse). The length and weight of worms correlated positively in both sexes. Total worm biomass increased linearly with increasing numbers of worms. However, whilst the length and weight of male worms declined with increasing worm burden (8.4 and 24.6% respectively), female worms were less affected, only length showing a significant reduction with increasing parasite burden (16.0%). Therefore, increasing worm burdens impeded growth of P. muricola, but reduction in length and weight were relatively small in relation to the overall size of this nematode. Increasing worm burdens were associated with loss of host weight and reduction in stomach weight and worm burdens in excess of 20 exerted a measurable cost to the host, which in the field, may be associated with loss of overall host fitness.     

Summertime activity patterns of common weaselsMustela nivalis vulgaris under differing prey abundances in grassland habitats

WeaselsMustela nivalis Linnaeus, 1766 in Kielder Forest, UK showed a diurnal rhythm of activity in summer and we argue that this is the prevailing rhythm found in weasels under natural conditions. Climatic conditions influenced weasel activity with weasels decreasing activity under rainy conditions, but we found no influence of month or weasel weight. In certain habitat types levels of weasel activity increased with increasing field voleMicrotus agrestis density. This result stands in contrast to results from studies carried out in the laboratory and may reflect a greater proportion of time spent in reproductive activity and intra-specific interactions in areas where vole density, and hence conspecific density is high.     

Influence of host strain and helminth isolate on the first phase of the relationship between rats and Moniliformis moniliformis (Acanthocephala)

Eleven trials, involving 440 rats bred from 3 laboratory strains and worms from 4 isolates of Moniliformis moniliformis, were carried out with each rat receiving an oral dose of 15 cystacanths. The results showed that the infectivity of the cystacanths was not affected by their age (range 55-194 days) or by their density per cockroach during development (16.1-88.6 cystacanths per cockroach). The numbers of worms per rat recovered at 35 days postinfection (p.i.) were shown to be related to rat strain, with highly inbred strains (PVG and F344) being more supportive of numbers of worms than an outbred Wistar strain. There was no evidence to suggest that the sex of the rats had any influence on the numbers of worms recovered at 35 days p.i. Evidence was obtained to suggest that smaller (younger) rats are likely to support more worms on average than larger (older) rats. There was no evidence of any relationship between worm weight and numbers of worms present per rat on day 35 p.i. Generally, rat strain had little effect on the dry weight (growth) of male M. moniliformis, in contrast to observations made for female worms. The greatest range of worm weights was observed from the recent isolate of the worm (1982) as compared with the well established isolate (1956) and the rats that supported most worms differed from those that harbored the largest worms. Rat sex was not observed to be associated with worm weight. The frequency distributions of numbers of M. moniliformis per rat were not described readily by the negative binomial distribution.     

Seasonal population dynamics of Pallisentis (Neosentis) celatus (Acanthocephala: Quadrigyridae) in the intestine of the rice-field eel Monopterus albus in China

Studies on the seasonal population dynamics of Pallisentis (Neosentis) celatus (Acanthocephala: Quadrigyridae) in the intestine of the rice-field eel Monopterus albus from the paddies and ditches in the Dong-ting Lake basin of China, were carried out with samples taken from June 2002 to May 2003. Prevalences were above 21% in all seasons sampled and with a distinct seasonal trend, which was highest (45.81%) in the spring and decreased by degrees. The mean intensity of infection was above 4.0 worms per fish. The maximum intensity of worms recovered from a single fish was 86 in the autumn of 2002. No significant seasonal differences were found in mean intensities, and differences in the mean abundance between winter and spring, winter and autumn were significant. Over-dispersed distributions of P. (N.) celatus in the host population, due to heterogeneity and feeding habits, were observed in all seasons. The size composition of both sexes of P. (N.) celatus showed males between 2.0 mm and 14.0 mm and females between 2.2 mm and 22.2 mm, with the main recruitment phase in the worm populations occurring in the summer and autumn, especially in the autumn, with the lowest recruitment occurring in the winter. The maturation and copulation of worms were mainly focused in the spring season. The sex ratio of female to male was both high in summer (1.09:1) and autumn (1.08:1). The higher proportion of females and the change in the worm sex ratio in summer can be attributed to the reduced longevity of male worms. As immature male worms exhibit a higher proportion of the worm population than females in all seasons, further studies are needed to determine if such a situation compensates for the shorter life span of males.     

Functional response of the least weasel, Mustela nivalis nivalis

We investigated the functional response of the least weasel ( Mustela nivalis nivalis ) in a series of experiments conducted in large outdoor enclosures (0.5 ha). Radiocollared Microtus voles were released in the enclosures at different densities (4, 8, 16 and 100/ha) three days before the release of a radiocollared weasel. During the three-day experiment every vole killed was replaced with another one as soon as possible to retain constant prey density. The results demonstrated type II functional response with the predation rate reaching 50% of the asymptotic rate at a vole density of 15 individuals per ha. More voles were killed at the highest densities than would be expected from the known energy demands of weasels. Female and male voles were killed in proportion to their abundances in the enclosures, and no difference in predation risk was detected between voles released in the enclosure before the weasel (residents) and during the experiment (transients).     

Seasonal population dynamics of Neoechinorhynchus qinghaiensis in the carp, Gymnocypris przewalskii przewalskii, from Qinghai Lake, China

Studies on the seasonal population dynamics of Neoechinorhynchus qinghaiensis (Acanthocephala: Neoechinorhynchidae) in its fish host Gymnocypris przewalskii przewalskii in the Qinghai Lake, China, were carried out with samples taken in May 1991, August 1992, November 1992 and February 1993. Prevalences were higher than 44% in all seasons. The mean intensity of infection was above 124 worms per fish. The maximum intensity of worms recovered from a single fish was 1402 in the autumn of 1992. Differences in the mean abundance, mean intensity and prevalence are not statistically significant relative to season and this is likely to be related to the stable temperatures recorded at the bottom of Qinghai Lake. Over-dispersed distributions of N. qinghaiensis in the host population, due to heterogeneity and feeding habits, were observed in all seasons. The size composition of both sexes of N. qinghaiensis showed males to be less than 3.5 mm and females between 0.5 and 4.25 mm, with the main recruitment phase in the worm populations occurring in the autumn, extending through winter and spring with the lowest recruitment occurring in the summer. The maturation and copulation of worms were mainly focused in the summer season. The sex ratio of female to male was both high in winter (1.51:1) and spring (1.48:1). The higher proportion of females and the change in the worm sex ratio in winter can be attributed to the reduced longevity of male worms. As immature male worms exhibit a higher proportion of the worm population than females in all seasons, further studies are needed to determine if such a situation compensates for the shorter life span of males.     

Field immobilization of American martens (Martes americana) and short-tailed weasels (Mustela erminea).

Ketamine hydrochloride (KH) and a 5:1 combination of KH and xylazine hydrochloride (XH) were used successfully to immobilize short-tailed weasels (Mustela erminea) and American martens (Martes americana), respectively. Four adult male martens were intramuscularly injected with 30 to 82 mg/kg KH and 8.0 to 16.4 mg/kg XH. Three adult male short-tailed weasels were intramuscularly injected with 20.8 to 42.1 mg/kg KH. Mean (+/- SE) induction times for martens and short-tailed weasels were 1.8 +/- 0.2 min and 46 +/- 4.1 sec, respectively; recovery times were 100.4 +/- 19.3 min and 97.9 +/- 6.3 min, respectively. Heart rate was relatively constant among martens; however, respiration varied widely (21 to 122 breaths per minute). Marten body temperature decreased between 0 and 20 min post-recumbency. Short-tailed weasel heart rate and respiration decreased in response to sedation until slightly before arousal. Body temperature stabilized by 20 min post-recumbency. Two short-tailed weasels tremored slightly within 10 min of arousal. I conclude that KH and KH/XH are safe immobilizing agents for martens and short-tailed weasels, respectively.