Metabolism and thermoregulation in the Cabrera vole (Rodentia: Microtus cabrerae)

Metabolism and thermoregulation were studied for the first time in the Cabrera vole (Microtus cabrerae), an endemic and threatened rodent of the Iberian Peninsula. Low values of resting metabolic rate (RMR) were registered (1.13 mlO(2) g(-1) h(-1)) at the lower limit of the thermoneutral zone (TNZ) (around 33.5 degrees C). Body temperature increased near the TNZ up to 37.3 degrees C but remained stable, around 36 degrees C, at ambient temperatures below 25 degrees C. Values of thermal conductance remained quite stable at ambient temperatures of 10-25 degrees C (0.144-0.160 mlO(2) g(-1) h(-1) degrees C) and increased to 0.301 mlO(2) g(-1) h(-1) degrees C at 33.5 degrees C. Data revealed that M. cabrerae developed a highly adaptive ability of conserving energy and lowering the metabolic cost of thermoregulation at high ambient temperatures, allowing the body temperature to approximate that of the environment and exhibiting low resting metabolic rate and high conductance.     

Is habitat selection by the Cabrera vole (Microtus cabrerae) related to food preferences?

The Cabrera vole (Microtus cabrerae) is an Iberian endemism considered threatened both in Portugal and Spain. This vole is often referred to as a tall perennial grassland community specialist. However, a recent study revealed that the Cabrera vole exploits a wide variety of grasslands in south Portugal. The major aim of the present study was to test the palatability of 21 plant species of this region occurring within or outside typical perennial grassland colonies in order to assess vole's food preferences. Results showed a major consumption of monocotyledons and annual plants (such as Festuca ampla, Agrostis castellana, Brachypodium distachyon, B. phoenicoides and Vulpia geniculata), but no relationship was found between diet selection and perennial grassland plant communities. The preference of voles for annual species, occurring more abundantly outside the colonies, raises the hypothesis that the establishment of a colony might be determined by plant species abundance and persistence over the year, rather than by their palatability. This seems to be particularly evident in this region, where summer meteorological conditions make vegetation unavailable outside the colonies.     

Vegetation analysis in colonies of an endangered rodent, the Cabrera vole (Microtus cabrerae), in southern Portugal

The Cabrera vole (Microtus cabrerae) is a threatened rodent endemic in the Iberian Peninsula with a patchy distribution and specific microhabitat requirements. This aim of this study was to document the composition of plant communities in habitats of Cabrera vole colonies in southern Portugal. Differences observed in plant species composition were also compared with vegetation structure, taxonomic and life form groups, species and group diversity, disturbance, topography and soil properties. Vegetation was sampled between March and July 2004, in 26 colonies occurring in five geographical areas. Grasses were the most abundant, common and diverse family in the colonies, and the perennial grass Agrostis castellana was present in 92% of colonies, with a mean cover of 16% of the site. Other frequently occurring species were Briza maxima (85%), Vulpia myuros (85%), Gaudinia fragilis (81%), Leontodon spp. (81%), Avena barbata (77%), Bromus hordeaceus (77%) and Tolpis barbata (77%). Colonies were classified in eight vegetation groups that included meadows, tall perennial grasslands, manured meadows with tall sedges, annual grasslands and ruderal and nitrophilous grasslands. Main gradients associated with composition differences were grass richness, annual and perennial grass cover, vegetation structure (herbaceous vegetation height), soil properties (texture and moisture), disturbance (ruderal species) and colony dimensions (area). Results suggest that the Cabrera vole is able to exploit a wide variety of grasslands, with a varying degree of ecological disturbance. Meadows and perennial grassland communities seem to be higher-quality microhabitats for voles.     

Achiasmatic giant sex chromosomes in the vole Microtus cabrerae (Rodentia, Microtidae).

Conventional and microspread preparations of Microtus cabrerae spermatocytes were made to investigate the chromosomes of this species. Three different types of Y chromosomes, varying in size of the heterochromatic block, were observed; they were alike, however, in regard to synapsis, which was consistently absent. Our results suggest that the heterochromatic blocks are not involved in the lack of synapsis and that asynapsis is a cytological feature common to all species of the family Microtidae. In addition, the co-aligned configuration of the ends of the sex-chromosome axes of this species and the lack of silver-stainable threads or filaments connecting them suggest the existence of two mechanisms for association of the sex chromosomes during prophase I and metaphase I: attachment of the ends of both sex chromosome axes to the nuclear envelope and heterochromatin "stickiness."     

Spatial segregation of two vole species (Arvicola sapidus and Microtus cabrerae) within habitat patches in a highly fragmented farmland landscape

Spatial segregation is one of the common mechanisms allowing the co-existence of similar interacting species in heterogeneous environments. Analysing spatial segregation requires information on individual home-range sizes and their degree of spatial overlap. In this study, we used radio-tracking to report for the first time the home-range and core-area sizes of sympatric Cabrera and water voles and to analyse intra- and inter-specific space sharing within habitat patches in a highly fragmented landscape. Results indicated that both species exhibited strong fine-scale site fidelity and reduced variation in range size across sexes and seasons. Monogamous mating system seemed to prevail for both species, although water voles may also exhibit polygynous breeding strategies. Mean home-range and core-area sizes of water voles (946.3 and 156.6 m²) were about twice that of Cabrera voles (418.2 and 55.1 m²). Within habitat patches, individuals of both species often overlapped their home ranges, particularly during the dry season (May–September), though intra-specific home-range overlap was generally higher than inter-specific overlap. Inter-specific space sharing was restricted to areas outside the centre of activity of animals, as no core-area overlap was ever recorded between Cabrera and water voles. Taken together, results support the view that co-existence of Cabrera and water voles in Mediterranean patchy habitats may in part result from spatial segregation among individuals, which may reflect competitive displacement or small-scale habitat partitioning. Results highlight the need to account for species interactions when designing conservation management strategies for sympatric Cabrera and water voles in fragmented landscapes.     

Chromosomal polymorphism of mandarin vole,Microtus mandarinus (Rodentia)

The mitotic and meiotic chromosomes of mandarin vole, Microtus mandarinus Milne-Edwards, from Shandong Province of China were analyzed by conventional, G- and C-banding and Silver-staining techniques. We detected chromosomal polymorphism in the vole, exhibiting diploid chromosome numbers 2n = 48-50 and variable morphology of the 1st pair, one medium sized telocentric pair and the X chromosomes. Four types of karyotypes were revealed in the population. According to banding analysis, there were pericentric inversion, Robertsonian fusion and translocation in M. mandarinus karyotype evolution. The X displayed two different morphologies, which could be explained by prericentric inversion and a telocentric autosome translocation.     

Shifts of thermogenesis in the prairie vole (Microtus ochrogaster)

Summary The weight-specific oxygen consumption ( ) of prairie voles caught in winter is 24% higher at 27.5° C and 29% higher at 7.5° C than that of summer animals, thus affording a higher weight-specific thermogenesis in winter than in summer which may allow tolerance to lower thermal exposures. Coincident with the increase in weight-specific rates of oxygen consumption is a decrease in body weight. When total energetic cost to maintain an animal per unit time is calculated, the cost at 27.5° C is the same for both summer and winter animals. Further, the cost to maintain an animal at 7.5° C is less in winter than in summer. Arguments are presented suggesting that prairie voles compensate for increased weight-specific thermogenesis in winter by lowering body weight. The responses to thermal acclimation are quite different in summer and winter animals, thus implying different sorts of metabolic organization. Acclimation to 5° C effects a 26% increase in at 27.5° C of winter voles, and acclimation to 30° C does not change . In contrast, at 27.5° C of summer animals is unaffected by 5° C acclimation, and depressed 20% by 30° C acclimation. Thus, the animals are capable of considerable physiological adjustment to varying thermal conditions in different seasons.     

Photoperiod influences reproduction in the prairie vole (Microtus ochrogaster)

Four experiments examined the role of photoperiod in the regulation of seasonal breeding in the prairie vole. Adult male voles maintained in short (8L:16D) as compared to long (16L:8D) photoperiods for 10 wk had reduced testicular and seminal vesicle weights, but fertility was not impaired. Male prairie voles reared from birth until 35 days of age in short as compared to long photoperiods also had reduced testicular and seminal vesicle weights, as well as diminished fertility. The incidence of pregnancy did not differ between long- and short-day female voles paired for 6 days with long- or short-day males (93%, 86%, 89%, and 88%, respectively). Photoperiod did not affect the incidence or the timing of postpartum pregnancies in long- or short-day females paired with long-day males through the birth of several litters. Adult male prairie voles retain only marginal sensitivity to short photoperiods, maturing males are highly responsive to short days, and adult females are insensitive to photoperiod. These data suggest that termination of the breeding season in the autumn may be due to the lack of fecund males in the population.     

Mapping the SRY gene in Microtus cabrerae: a vole species with multiple SRY copies in males and females.

The SRY gene is a single-copy, male-specific gene, located on the Y chromosome in most mammals. However, recently we have described the presence of multiple polymorphic copies of this gene in both males and females of the vole species Microtus cabrerae. Here, we present the chromosomal localization of SRY gene copies in this species by fluorescent in situ hybridization (FISH). This technique localized these gene copies in the short arm, and hence in the euchromatic region, of the Y chromosome. Furthermore, several copies of the SRY gene are located on the X chromosome. These copies are spread along the entire heterochromatic region of the X chromosome, occupying the whole short arm, the centromeric region, and the pericentromeric region of the long arm.     

The correlation between demography and metabolic rate: a test using the beach vole (Microtus breweri) and the meadow vole (Microtus pennsylvanicus)

Summary This study examines the hypothesis that mammalian species with wide fluctuations in population size will have greater metabolic rates than species with smaller population fluctuations. We tested this hypothesis using two microtine rodents — the beach vole (Microtus breweri) and the meadow vole (M. pennsylvanicus). Although these species experience similar climatic regimes, eat similar foods, and have a very close phylogenetic relationship, they show marked differences in demography. Microtus pennsylvanicus is prone to large supraannual fluctuations in population size, while M. breweri is essentially acyclical. Metabolic rate (oxygen consumption) of each species was measured using open-flow respirometry at ambient temperatures ranging from 2 to 34° C. Basal metabolic rate of M. pennsylvanicus (1.81 ml O₂ g^–1 h^–1) was significantly greater than that of M. breweri (1.39 ml O₂ g^–1 h^–1). The lower critical temperature, estimated by continuous two-phase regression, was 28.9° C for M. pennsylvanicus and 29.8° C for M. breweri. Regression lines below thermoneutrality did not differ in slope, but the elevation for M. pennsylvanicus was significantly higher. Thus, M. pennsylvanicus has a higher metabolic rate at all temperatures examined. These results support the hypothesis that metabolic rate is positively correlated with the extent of population fluctuation. We suggest that further evidence for, or against, this hypothesis should be found by comparing closely matched species pairs, rather than resorting to confounded allometric comparisons of ecologically and phylogenetically diverse taxa.     

The development of social behaviour in the vole (Microtus agrestis)

Juvenile voles of the species Microtus agrestis investigated the bodies of other juveniles with the nose, by touching the dorsal surface from snout to tail. Play movements often followed such nosing contacts and augmented further contacts. The most important scent stimulating play was produced by the skin at the back of the head. The secretion of the nose and mouth region may convey sexual identity, the rump region and feet individual identity.
Young born in the spring and early summer often interacted and played, the autumn young seldom. The behaviour of overwintering sexually immature adults was similar to that of the autumn juveniles. It is suggested that this seasonal difference in the behaviour of juveniles has consequences for subsequent mature males, and that this developmental factor may have an important effect on the annual population cycle.     

Fine-scale genetic structure and dispersal in the common vole (Microtus arvalis)

The genetic structure and demography of local populations is tightly linked to the rate and scale of dispersal. Dispersal parameters are notoriously difficult to determine in the field, and remain often completely unknown for smaller organisms. In this study, we investigate spatial and temporal genetic structure in relation to dispersal patterns among local populations of the probably most abundant European mammals, the common vole (Microtus arvalis). Voles were studied in six natural populations at distances of 0.4-2.5 km in three different seasons (fall, spring, summer) corresponding to different life-history stages. Field observations provided no direct evidence for movements of individuals between populations. The analysis of 10 microsatellite markers revealed a persistent overall genetic structure among populations of 2.9%, 2.5% and 3% FST in the respective season. Pairwise comparisons showed that even the closest populations were significantly differentiated from each other in each season, but there was no evidence for temporal differentiation within populations or isolation by distance among populations. Despite significant genetic structure, assignment analyses identified a relatively high proportion of individuals as being immigrants for the population where they were captured. The immigration rate was not significantly lower for females than for males. We suggest that a generally low and sex-dependent effective dispersal rate as the consequence of only few immigrants reproducing successfully in the new populations together with the social structure within populations may explain the maintenance of genetic differentiation among populations despite migration.     

Role of photoperiod during pregnancy and lactation in the meadow vole, Microtus pennsylvanicus

The influence of daylength on body mass and food intake of pregnant and lactating voles was tested by comparing animals housed in long versus short daylengths. Pregnancy rates were approximately 50% in long-day females and in voles kept in short days beginning 2 weeks before mating, but were significantly lower in voles preadapted to short days for 8 weeks before mating. Body mass and food intake increased substantially during pregnancy and lactation and the magnitude of the increase was unaffected by daylength; by contrast, body weight was significantly reduced in non-impregnated voles kept in short as compared to long days. The suppressive effects of short photoperiods on body weight were completely counteracted during pregnancy and lactation. Voles that breed during the short days of winter face extreme energetic challenges but the advantages of early breeding appear to justify the costs.     

First report of Siphonaptera infesting Microtus (Microtus) cabrerae (Rodentia-Muridae-Arvicolinae) in Cuenca,Spain and notes about the morphologic variability of Ctenophthalmus (Ctenophthalmus) apertus personatus (Insecta-Siphonaptera-Ctenophthalmidae)

The fleas infesting Microtus (Microtus) cabrerae from three different areas of Cuenca province (Spain) have been studied. It is the first time that on ectoparasitological study of this badly known rodent has been done. Four Siphonaptera species have been detected: Rhadinopsylla (Actenophthalmus) pentacantha, Peromyscopsylla spectabilis spectabilis, Nosopsyllus fasciatus and Ctenophthalmus (Ctenophthalmus) apertus personatus, which was the most abundant species (26 males and 31 females of a total of 28 males and 35 females). Considering the great morphologic variability within the male processus basimerus ventralis (p.b.v.) of segment IX of C. personatus subspecies, three morphotypes have been recognised. The male polymorphism detected, would be the result of both host confinement and genetic selection acting on the parasite. It should be pointed out that C. (C.) apertus personatus is not narrowly host-specific, therefore further studies are required to clarify this taxonomic situation.