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).     

Microsatellite markers for genetic studies in the weasel (Mustela nivalis)

This study reports the first set of microsatellite markers for the weasel (Mustela nivalis). We chose to isolate loci with tetranucleotide repeat motifs because they can be scored less ambiguously than the more commonly used dinucleotide loci. All 11 loci showed considerable variation within a population sample of 28 individuals from Portugal, with number of alleles ranging from four to nine per locus and observed and expected heterozygosities ranging from 0.21 to 0.86 and from 0.40 to 0.84, respectively. No linkage disequilibrium was detected between pairs of loci, and only one locus (Mn 1.30) deviated from Hardy–Weinberg equilibrium expectations in the analyzed population sample. Among the 11 loci, Mn 1.30 was the only one for which all known males were homozygous. Analysis of an additional population sample of 23 individuals (14 males and 9 females) from Denmark revealed that all males, but only four females, were homozygous for Mn 1.30, supporting the idea that the locus is X-linked. These novel polymorphic microsatellite markers should be useful in studies of population genetics and molecular ecology of the weasel.     

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.     

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 weasel (Mustela nivalis) helps in detectingDemodex mites in rodents

Many stages of parasites living in or on prey animals can pass undestroyed through the intestinal tract of carnivores and carnivorous animals. Nematode eggs, whole nematodes, even cestodes can be found in their faeces, but of the ectoparasitic mites usually only the eggs are found. It was therefore surprising thatDemodex mites, some of them even still alive, were found to have been passed by a captive weasel.Members of the genusDemodex cannot be detected by routine procedures yielding ectoparasites. Most species do not give rise to pathological alterations and the site they inhabit may not be known. To isolate them, either the skin complex or the organ supposed to containDemodex has to be digested with KOH or else the mites have to be squeezed out of the follicles. Compared to this, the weasel method is very simple.Faecal pellets (not more than one or two) are carefully ground with a mortar in a saturated ZnSO₄ solution and poured through a fine mesh into a test tube so as to form a little mountain at the orifice. The tube is allowed to stand for 25–30 min. Due to their lower specific weight, protozoan oocysts, worm and mite eggs and the specimens ofDemodex rise to the surface. The meniscus is then touched with a cover slip and, with the adhering drop, is placed on a slide. In the case of the parasites mentioned here, the procedure can be repeated once more after 5 min. Demodex mites and all their developmental stages, including the eggs, appear in a clean preparation on the slide, ready to be measured, drawn, or photographed. The mites are in excellent shape. Some of them even move their gnathosome and legs, if fresh faeces are submitted to the concentration technique; the method is very quick, with results being obtained within 30 min. Although only one rodent can be fed to a weasel per day, it takes a minimum of labour to examine the faeces, which can also be stored in a refrigerator.As the weasel was young when caught, it was not restricted in its feeding habits to the common vole (Microtus arvalis) which is its main prey in Middle Europe, but took other rodents, too. This proved to be very helpful when two different rodent species were to be tested forDemodex. In order not to mix them up, a white mouse of aDemodex-free stock was given on the day between. By this it was also possible to make a semi-quantitative survey of theDemodex population size of one host animal, because the faecal pellets of a weasel are very small and can be entirely used. All available rodents can be tested by this method. If the weasel is hungry it might even be possible to feed only the parts of the body of bigger host animals suspected to containDemodex.The disadvantages of the weasel method are that (a) no permanent mounts can be made, because the zinc sulfate (or any other saturated solution commonly used for these purposes) forms crystals when a mounting medium is added, and (b) the site inhabited by the mites has still to be ascertained; this is particularly important, since one host species can harbour more than oneDemodex species, and these may look very similar.     

Trade-offs between activity and thermoregulation in a small carnivore,the least weasel Mustela nivalis

We studied factors influencing daily energy expenditures (DEE) of male least weasels (Mustela nivalis) using the doubly labelled water technique. The relationship between ambient temperature and DEE formed a triangular pattern, characterized by invariance of the maximum DEE and an inverse relationship between minimum DEE and temperature. A simple energetic model relating the DEE of male weasels to activity time (AT) and ambient temperature predicted that, across seasons, less than 10 per cent of measurements approach the upper bound of observed DEE. Male weasels were able to maintain a relatively constant maximum energy output across varying temperatures by adjusting their AT to changes in temperature. They achieved maximum energy expenditures in winter due to high thermoregulatory costs, and in spring and summer due to high levels of physical activity. This pattern exemplifies a ‘metabolic niche’ of a small mammal having extremely high energy expenditures primarily driven by ambient temperature.     

A population study of the metastrongylid nematode Skrjabingylus nasicola in the weasel Mustela nivalis

Analyses of adult worms of Skrjabingylus nasicola occurring in the nasal sinuses of the weasel Mustela nivalis from three localities in the British Isles show that the intensity of infestation can be correlated with increasing severity of skull damage, which in turn increases as the weasel ages. It is suggested that, apart from hormonal differences, the smaller sized female skull is likely to be linked with lower levels of infestation in female compared with male weasels. Also a reduction in mean worm length in female skulls and in heavy infestations of S. nasicola is probably the result of a "crowding effect", previously described for other helminth infections in the definitive host. Crowding appears to have no effect on the sex ratio of worm populations, although there is a tendency for the ratio of female: male worms to increase in female weasels. Reasons for this are discussed.     

Radiocarbon evidence for a prehistoric deliberate translocation: the weasel (Mustela nivalis) of Mallorca

We present radiocarbon evidence for the presence of the weasel (Mustela nivalis) on Mallorca prior to the Roman colonization of the Balearics. Bone collagen from a single specimen recovered at Cova del Ninot, Mallorca rendered two radiocarbon ages, independently obtained at two laboratories (2σ interval: 386–206 cal BC). These dates indicate that the translocation of the weasel to Mallorca occurred in Late Prehistory. The inhabitants of Mallorca at that time were the Talaiotic people (Iron Age settlers of the Balearics). The weasel appears to have been introduced by Talaiotic mercenaries returning to the island on Carthaginian ships. This is the first documented case of the translocation of a wild carnivorous mammal to the Gymnesic Islands (i.e., Mallorca and Menorca) in prehistoric times. Some ecological consequences of this invasion are outlined.     

Large-scale spatial and temporal patterns in population dynamics of the stoat, Mustela erminea, and the least weasel, M. nivalis, in Finland

The stoat and the least weasel are specialist predators of small rodents, and therefore their numbers are likely to depend on the availability of voles. These small predators are ecologically alike, but they differ somewhat in their diet. The stoat is larger in size than the least weasel and therefore capable of using a wider variety of prey species, while the least weasel is more restricted to small mammals. Voles in northern Fennoscandia exhibit cyclic dynamics of 3–5 years with large-scale spatial synchrony and geographical trends in cycle length and amplitude. We predicted that the cyclic dynamics of voles are reflected in the dynamics of their predators with slight differences between the stoat and the least weasel. In this study we use snow-tracking data to characterize the dynamics of small mustelids. The data were collected from different parts of Finland using permanent triangle-shaped census routes of 12 km in 1989 to 2003. Population fluctuations of small mustelids were generally multiannually periodic and in synchrony over large areas, but we did not find any clear geographical gradient in the attribute of small mustelid dynamics comparable to those observed in vole population fluctuations. Instead, we found a similar decreasing temporal trend in the abundances of both species as has been recently reported for voles.     

Phylogeography and population history of the least weasel (Mustela nivalis) in the Palearctic based on multilocus analysis

The least weasel (Mustela nivalis) is one of the most widely distributed carnivorans. While previous studies have identified distinct western and eastern mitochondrial DNA (mtDNA) lineages of the species in the western Palearctic, their broader distributions across the Palearctic have remained unknown. To address the broad-scale phylogeographical structure, we expanded the sampling to populations in Eastern Europe, the Urals, the Russian Far East, and Japan, and analyzed the mtDNA control region and cytochrome b, the final intron of the zinc finger protein on Y chromosome (ZFY), and the autosomal agouti signaling protein gene (ASIP). The mtDNA data analysis exposed the previous western lineage (Clade I) but poorly supported assemblage extending across Palearctic, whereas the previous eastern lineage (Clade II) was reconfirmed and limited in the south western part of the Palearctic. The ZFY phylogeny showed a distinctive split that corresponding to the mtDNA lineage split, although less phylogeographical structure was seen in the ASIP variation. Our data concur with the previous inference of the Black Sea–Caspian Sea area having an ancestral character. The Urals region harbored high mitochondrial diversity, with an estimated coalescent time of around 100,000 years, suggesting this could have been a cryptic refugium. Based on the coalescent-based demographic reconstructions, the expansion of Clade I across the Palearctic was remarkably rapid, while Clade II was relatively stable for a longer time. It seems that Clade II has maintained a constant population size in the temperate region, and the expansive Clade I represents adaptation to the cold regions.     

Studies of the metabolism,food consumption and assimilation efficiency of a small carnivore,the weasel (Mustela nivalis L.)

Summary The average respiratory quotient of weasels was 0.73. There were significant differences in average daily metabolic rate (ADMR) between the sexes and six experimental temperatures. As temperature decreased the mean ADMR increased, with a relatively greater rise for females. Regression equations of ADMR on temperature were Y=483.2–9.6X kcal/kg/day for males, and Y=625.3–15.0X kcal/kg/day for females. The minimum metabolic rate measured for males was 6.6 kcal/kg/h, and the maximum 25.7 kcal/kg/h. The relationship between ADMR and body weight varied with different temperatures, but was consistent with the hypothesis that ADMR was proportional to metabolic weight. The energetic costs of activity for my captive weasels were more than 20% of their daily total energy expenditure. Data on metabolism supported the conclusion that long, thin mustelids lose heat faster than normally-shaped mammals of the same weight.The calorific contents of foods, faeces and urine from feeding trials were determined. There were significant differences in the calorific content of faeces between the sexes, and of faeces and urine between diets.Four natural foods (Microtus, Apodemus, rabbit, starling) were offered during feeding trials. Daily food consumption varied between the diets, but small weasels always ate relatively more than large ones. Mean consumption was 0.33 g/g/day for males, and 0.36 g/g/day for females. Weasels on low-bulk diets (rabbit, starling) lost at least as much energy in urine as in faeces. There were significant differences in assimilation efficiency between the sexes and diets. The average efficiency for males was 78.2%, and 79.8% for females. Bulky foods lowered assimilation efficiencies by up to 9%.Daily energy requirements for maintenance calculated from ADMR data were compared with those from feeding trials. On the Microtus diet weasels expended 18.6–30.1% more energy on maintenance than predicted by the ADMR results, whereas on the other diets they expended 2.7–31.4% less energy. Estimates from ADMR data were probably more accurate.     

On the occurrence of the Weasel,Mustela nivalis,in Turkey

Abstract

It was shown that the Weasel is distributed over the whole of Anatolia The species’ considerable size, the occasional occurrence of a white winter coat and the existence of two types of Weasels (nivalis type and minuta type) in Turkey have often lead to the wrong assumption that the Stoat (M. erminea) also occurs in Turkey.     

Environmental and genetic influences on body mass and resting metabolic rates (RMR) in a natural population of weasel Mustela nivalis

Body mass (BM) and resting metabolic rates (RMR) are two inexorably linked traits strongly related to mammalian life histories. Yet, there have been no studies attempting to estimate heritable variation and covariation of BM and RMR in natural populations. We used a marker‐based approach to construct a pedigree and then the ‘animal model’ to estimate narrow sense heritability (h²) of these traits in a free‐living population of weasels Mustela nivalis—a small carnivore characterised by a wide range of BM and extremely high RMR. The most important factors affecting BM of weasels were sex and habitat type, whereas RMR was significantly affected only by seasonal variation of this trait. All environmental factors had only small effect on estimates of additive genetic variance of both BM and RMR. The amount of additive genetic variance associated with BM and estimates of heritability were high and significant in males (h² = 0.61), but low and not significant in females (h² = 0.32), probably due to small sample size for the latter sex. The results from the two‐trait model revealed significant phenotypic (r_P = 0.62) and genetic correlation (r_A = 0.89) between BM and whole body RMR. The estimate of heritability of whole body RMR (0.54) and BM corrected RMR (0.45) were lower than estimates of heritability for BM. Both phenotypic and genetic correlations between BM corrected RMR and BM had negative signals (r_P = ?0.42 and r_A = ?0.58). Our results indicate that total energy expenditures of individuals can quickly evolve through concerted changes in BM and RMR.     

Comparative phylogeography between the ermine Mustela erminea and the least weasel M. nivalis of Palaearctic and Nearctic regions, based on analysis of mitochondrial DNA control region sequences

Phylogeography of the ermine Mustela erminea and the least weasel M. nivalis from Palaearctic and Nearctic regions were investigated based on mitochondrial DNA control region sequences. Mustela erminea exhibited a very low level of genetic variation, and geographic structures among populations were unclear. This may indicate that M. erminea recently reoccupied a wide territory in Eurasia following the last glacial retreat. In comparison with M. erminea, genetic variations within and among populations of M. nivalis were much greater. Molecular phylogenetic relationships showed that two lineages of M. nivalis occurred in the Holarctic region: one spread from the Eurasian region to North America, and the other occurred in south-eastern Europe, the Caucasus and Central Asia. The results suggest either mitochondrial DNA introgression among populations of south-eastern Europe, the Caucasus and Central Asia, or ancestral polymorphisms remaining in those populations. Contrastive phylogeographic patterns between the two mustelid species could reflect differences of their migration histories in Eurasia after the last glacial age.     

Effects of temporal variation in the risk of predation by least weasel (Mustela nivalis) on feeding behavior of field vole (Microtus agrestis)

Predation risk tends to vary in time. Thus prey animals face a problem of allocating feeding and antipredator effort across different risk situations. A recent model of Lima and Bednekoff (1999) predicts that a prey should allocate more feeding effort to low risk situations and more antipredator effort to high risk situations with increasing relative degree of risk in high risk situations (attack ratio). Furthermore when the proportion of time the prey spends in the high risk situation (p) increases, the prey have to eventually feed also in the high risk situations. However the increase in feeding effort in low risk situations should clearly exceed that in high risk situations as p increases. To test these predictions we measured feeding effort of field voles (Microtus agrestis) exposed to varying presence of least weasel (Mustela nivalis) and its feces in laboratory conditions. We generated quantitative predictions by estimating attack ratios from results of a pilot experiment. The model explained 15% of the observed variation in feeding effort of voles. Further analyses indicated that feeding effort was lower in high risk situations than in low risk situations at high attack ratio, but not at a lower one. Voles exposed to a presence of a weasel for extended periods showed signs of nutritional stress. Still we did not find any increase in feeding effort with increasing p. This was obviously due to the relatively low maximal p we used as we included only conditions likely to occur in nature.