A comparative study of resting metabolic rate was conducted for the temperature range 10-37 °C for four rodent species, northern three-toed jerboa (Dipus sagitta) (body mass, Mb 79.2±6.8 g, n = 25), midday gerbil (Meriones meridianus) (Mb = 45.0±8.1 g, n = 10), desert hamster (Phodopus roborovskii) (Mb = 15.4±2.9 g, n = 26, and striped hamster (Cricetulus barabensis) (Mb = 24.8±4.0 g, n = 7) in the Ordos desert in summer (July), 1997. The minimum resting metabolic rates were 1.14±0.25 ml O2/g.h for three-toed jerboa, 1.35±0.3 ml O2/g.h for midday gerbil, 2.98±0.65 ml O2/g.h for desert hamster, and 2.75±0.37 ml O2/g.h for striped hamster. The thermal neutral zones (TNZ) were wide in the three desert species that was 26~37 °C in jerboa, 26~35 °C in gerbil, and 24~34 °C in desert hamster, respectively. For the non-desert species, striped hamster, it was 26~30 °C. The results do not confirm the hypothesis that desert rodents generally have lower metabolic levels than non-desert species. The high metabolic rates of these four rodent species were interpreted to be influenced by the stable availability of food resources and low environmental temperature in the Ordos Plateau. our results partly support the hypothesis that the metabolism characteristics are determined by food resources and environment temperature for animals living in arid regions.
We studied the demography and spatial structure of the muskrat population at the Nizhnekamsk Reservoir in central Russia. 45Ca radioactive prenatal labelling of muskrats was performed over a period of eight years. A total of 3,876 infividual muskrats were captured from a 12 km2 experimental plot and analysed on the basis of age, sex and presence of radioactivity. During the first year of life, the highest mortality was among muskrats from the latest litter, whilst during the second year of life it was amongst individuals from the earlier litters. Spring and autumn muskrat migration were studied and we observed a cyclical type of spatial structuring within the population. The proportion of individuals migrating in autumn varied from 18-57%, but significant differences in the migratory activities of different age groups were not observed. We found several tendencies throughout the eight years: a decrease in the proportion of the first litter (not overwintering), an increase in the proportion of third litters, and a decrease in the proportion of yearlings born in the first litter - we assume these represent responses to flooding.
We examined the capacity for nonshivering thermogenesis in four rodent species residing in the Ordos Plateau of Inner Mongolia. Nonshivering thermogenesis (NST, maximum NST minus resting metabolic rate) was determined for northern three-toed jerboas (Dipus sagitta), midday gerbils (Meriones meridianus), desert hamsters (Phodopus roborovskii), and striped hamsters (Cricetulus barabensis) in spring (May), summer (July, and autumn (OCtober) captured in the Kubuqi desert in 1997. NST was induced by norepinephrine (NE) and measured by using the closed-circuit respirometer at 27 °C. Our results showed significant increases from summer to autumn in NST for the four species. NST capacities were 0.52±0.27 ml O2/g0.73.h (n = 7) in summer and 2.49±1.29 (n = 6) in autumn for jerboas, 1.61±0.74 (n = 6) in summer and 3.26±1.35 (n = 5) in autumn for gerbils, 3.62±0.75 (n = 5) in summer and 9.71±2.81 (n = 6) in autumn for desert hamsters, and 6.81±3.02 (n = 8) in summer and 11.23±2.77 (n = 8) in autumn for striped hamsters. These results suggest that small mammals living in the inland arid region on Ordos Plateau adapt to their extreme environment physiologically by adjusting their thermogenic capacities to cope with the dramatic seasonal temperature fluctuations.
Mongolian gerbils are territorial and live in family groups with established, stable male-female pairs. The objectives of this study were to investigate whether locomotor activity indicates female receptivity, and to evaluate the impact of a male on the stability of the female sexual cycle. To prevent gravidity, males were sterilised by vasectomy. Nevertheless, they behaved like intact males, displayed copulatory behaviour, and had normal mean serum testosterone levels of 1.1±0.2 ng/ml. Oestrus caused modulations in the activity pattern and hence influenced locomotor activity; female receptivity was reflected by an advance in the onset of activity. Male presence led to prolonged and irregular oestrus cycles in females. Three pairs were stable and nearly no attacks occurred for nine months. However, in four pairs, females suddenly attacked males. Males displayed flight and appeasement behaviours, but two died within 24 hours, and two were severely injured and had to be separated. Two of these females were paired again to other vasectomised males, but killed their cagemates after 3.5 and 12.5 weeks, respectively. In total, six of nine pairs were disrupted by female aggression, four males were killed and two males were separated but presumably would have otherwise died. Females presumably detected male infertility by repeated unsuccessful matings without sperm transmission and/or by physical impairments due to repeated pseudopregnancy. As a result they no longer invested in pair bonds that would eventually diminish their reproductive fitness.
More than one thousand rodent remains have been found in three different lacustrine sediment beds of Miocene age at Bełchatów (Poland) - an opencast brown coal mine. Three fossil assemblaged (Bełchatów C - the oldest, Bełchatów B and Bełchatów A) contain abundant rodent remains (mainly teeth) and correspond to biostratigraphic zone MN 4/5, MN 5/6 and MN 8/9, respectively. Aboud 80% of the rodent material was found in the uppermost layer (Bełchatów A). The remaining two assemblages, of not dissimilar ages and with similar Orleanian/ Astaracian faunas, countain 11% (Bełchatów B) and 9% (Bełchatów C) of the material studied. Most species (except for the relatively numerous Sciuridae and Castoridae and one dipodid tooth) have already been described. However, recent studies on cricetids and eomyids have led to a revision of the previously proposed ages of Bełchatów C and Bełchatów A.
Based on ecological parameters of 15 localities with birch mouse (Silista betulina) occurrence a model of its potential distribution in a part of the Bohemian Forest (Šumava) in Czech Republic was set up. The following habitat parameters were included into the model: land cover (six classes), proximity to next cover type (ten classes), proximity to a stream (five classes), altitude (seven classes), slope (seven classes), exposition (four classes). These parameters were derived from the Landsat 5 TM data and from digital elevation model using EASE/PACE software. All raster format data had a 30 m pixel size and all geographical information system layers were rectified into maps scale 1 " 25,000, Gauss-Krüger projection. For each of the six parameters two histograms were calculated. The first one displayed the frequency of a membership of a pixel to a class under a mask of the whole study area and the second histogram under a mask of the area of the birch mouse occurrence. The birch mouse preferred: the closest proximity to a stream (0-60m), flat terrain (slope < 5°), north-eastern and south-eastern expositions, the altitude between 700-900 m a. s. l., unmanaged meadows and pasture, boundaries between meadows and pastures or meadows and forests. The overall probability of the occurrence calculated according to these factors revealed areas of the most probable occurrence above all along the Vltava river system. This model was successfully verified by pitfall trap collection of birch mouse in three randomly chosen localities with the highest calculated probability of the occurrence.
Two chromosomal races of the house moue occur in central Tunisia: a standard type (2n = 40) and a Robertsonian race (2n = 22). Although contact between races is not restricted, hybrid populations are rare. Patterns of mate preference between wild mice of the two races suggest that, although incipient, this premating divergence could limit the number of crosses between races in nature. In this paper we compare sexual preference of laboratory-born mice and their parents caught as adults in the wild with the aim to assess whether the social context of development to adulthood could influence expression of preference. We predict that in the absence of such influence, parents and laboratory-born offspring should show a comparable pattern of preference. Results show that offspring preference is always lower than and not related to that of their parents. However, a significant pair effect exist leading us to group parents and offspring into three categories according to the parents' preference: homokaryotypic, heterokaryotypic, or dissimilar. Offspring exhibit a preference, which is consistent with that of their parents, only in two cases: male offspring of the standard race when both parents show a heterokaryotypic preference; all offspring when the homokaryotypic preference of fathers is high. Discrepancy between preferences of wild-caught mice and their laboratory-born progeny suggests that, here, preference may be partly influenced by social conditions experienced before and during adulthood.
Type populations of four fossil species of voles belonging to the genus Mimomys are redescribed. Mimomys ostramosensis is a large-sized, hypsodont Mimomys with enamel islet, Mimomys-ridge and relatively abundant cement. Mimomys tornensis, a medium-sized vole, is characterized by lack of typical Mimomys-ridge and islet present only in M3/, with very abundant cement accumulation. Mimomys pitymyoides, a medium-sized Mimomys, with broadly confluent triangles, is distinguished by the presence of islets and Mimomys-ridge in most specimens relatively low tracts and differentiation of enamel thickness not so distinct as in other Mimomys species. Mimomys pusillus is a small-sized vole with islet present only in younger wear stages, relatively frequent Mimomys-ridge and relatively low tracts.