Vegetation differences caused by pine vole mound building in subalpine plant communities in the Spanish Pyrenees

The influence of mediterranean pine vole (Microtus (Terricola) duodecimcostatus) mound-building activity in two Western Spanish Pyrenees plant communities (Mesobromion erecti and Festucion eskiae-Nardion strictae) were studied. The plants colonizing the gaps in these areas are different in the two cases considered. The plant composition of surrounding plant communities seems to be the main factor in revegetation. Mound-building activity changes the species' relative frequency and life-form spectrum, decreases the monocytyledonous/dicotyledonous ratio and increases diversity by diminishing the presence of dominant plant species.Abbreviations ME Mesobromion erecti - FN Festucion eskiae-Nardion strictae - (monocots) Monocotyledonous - (dicots) Dicotyledonous     

Natal dispersal in relation to population density and sex ratio in the field vole,Microtus agrestis

Summary In a sample of 240 juvenile field voles 8% of the males and 22% of the females reached sexual maturity within their natal home range. Among individuals retrapped as adults, 58% of males and 23% of females had dispersed, i.e. had moved more than one home range diameter. The mean distance moved for males (58.5 m) exceeded that for females (28.6 m). Male movement distances were negatively associated with total density, and with density of adult females, but not with male density. Female movements were not related to population density. There were no relation between sex ratio and distance moved. The distribution of distances moved for both males and females fit a geometrical distribution, suggesting the importance of competitive processes.     

Summer acclimatization in the short-tailed field vole,Microtus agrestis

We investigated the changes that occurred in basal and noradrenaline-induced metabolic rate, body temperature and body mass in short-tailed field voles,Microtus agrestis, during exposure to naturally increasing photoperiod and ambient temperature. These parameters were first measured in winter-acclimatized voles (n=8) and then in the same voles which had been allowed to seasonally acclimatize to photoperiod and ambient temperature (6 months later). Noradrenaline induced metabolic rate, basal metabolic rate and nonshivering thermogenesis were significantly higher in winter-acclimatized compared to summer-acclimatized voles. There was a significant positive relationship between basal metabolic rate and noradrenaline-induced metabolic rate. Body mass was significantly higher in summer-acclimatized compared to winter-acclimatized voles. There was a significant positive relationship between body mass and noradrenaline-induced metabolic rate in both winter-acclimalized and summer-acclimatized voles; however, there was no relationship between basal metabolic rate and body mass in either seasonal group of voles. Body temperature after measurements of basal metabolic rate was not significantly different in the seasonal cohorts of voles. However, body temperature was significantly higher in winter-acclimatized compared to summer-acclimatized voles after injection of noradrenaline. Previously we have found that a long photoperiod was not a sufficient stimulus to reduce thermogenic capacity in winter-acclimatized voles during cold exposure, since basal metabolic rate increased to compensate for a reduction in regulatory nonshivering thermogenesis. Here we found that a combination of increased ambient temperature and photoperiod did significantly reduce thermogenic capacity in winter-acclimatized voles. This provided evidence that the two aspects of non-shivering thermogenesis, obligatory and regulatory, are stimulated by different exogenous cues. Summer acclimatization in the shorttailed field vole is manifest as a significant decrease in both basal and noradrenaline-induced metabolic rate, combined with a significant increase in body mass.Abbreviations ANCOV A analysis of covariance - BAT brown adipose tissue - BM body mass - BMR basal metabolic rate - NST non-shivering thermogenesis - NA noradrenaline - V the maximum V recorded following mass specific injection of noradrenaline - V the maximum V recorded following mass specific injection of saline - T _a ambient temperature - T _b rectal body temperature - T _1c lower critical temperature - UCP uncoupling protein - V oxygen consumption     

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.     

Food deprivation in the common vole (<Emphasis Type="Italic">Microtus arvalis</Emphasis>) and the tundra vole (<Emphasis Type="Italic">Microtus oeconomus</Emphasis>)

Arvicolinae voles are small herbivores relying on constant food availability with weak adaptations to tolerate prolonged food deprivation. The present study performed a comparative analysis on the responses to 4–18 h of food deprivation in the common vole (Microtus arvalis) and the tundra vole (Microtus oeconomus). Both species exhibited rapid decreases in the plasma and liver carbohydrate concentrations during phase I of fasting and the decline in the liver glycogen level was more pronounced in the tundra vole. The plasma thyroxine concentrations of the common vole decreased after 4 h. Lipid mobilization (phase II of fasting) was indicated by the increased plasma free fatty acid levels after 8–18 (the common vole) or 4–18 h (the tundra vole) and by the elevated lipase activities. In the tundra vole, the plasma ghrelin concentrations increased after 12 h possibly to stimulate appetite. Both species showed increased liver lipid concentrations after 4 h and plasma aminotransferase and creatine kinase activities after 12–18 h of food deprivation implying liver dysfunction and skeletal muscle damage. No signs of stimulated protein catabolism characteristic to phase III of fasting were present during 18 h without food.     

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.     

Genetic control of enzyme polymorphisms in the California vole,Microtus californicus

Inheritance of 15 polymorphic isozymes was investigated in captive Microtus californicus. Eleven of the isozymes show patterns consistent with a Mendelian model of inheritance: glycerol-3-phosphate dehydrogenase (GPD), lactate dehydrogenases A and B (LDH-A and LDH-B), malic enzyme 2 (ME-2), isocitrate dehydrogenase 1 (ICD-1), phosphogluconate dehydrogenase (PGD), glutamate-oxaloacetate transaminase 1 (GOT-1) phosphoglucomutase 2 (PGM-2), leucine aminopeptidase (LAP), glucosephosphate isomerase (GPI), and esterase 2 (ES-2, from kidney). four of the isozymes show patterns that cannot be interpreted by a simple genetic model: esterases 1 and 4 (ES-1, ES-4, from hemolysate), esterase 3 (ES-3, from plasma), and protein 1 (PT-1). The following pairs of loci are assorting independently: LAP and PGD, LAP and PGM-2, GOT-1 and PGD, GOT-1 and GPD, LAP and GPD, GPD and PGD, GPI and PGD. Data from one test cross mating indicate that GPD and PGM-2 are loosely linked with recombination about 30%. Additional data are needed to confirm this relationship.This study was conducted while the first author was the recipient of an NIH Traineeship. The Departments of Genetics and Zoology provided financial support for the maintenance of the animal colony. This work was supported in part by an NIH-Biomed grant (3-S05-RR-07006-08S1) to W. Z. Lidicker.     

Adult philopatry and dispersal in the field vol Microtus agrestis

Summary Using mark-recapture data, we related the movements of adult field voles to population density, sex ratio and population growth. Dispersal movements (defined as distances larger than 1 home range diameter) were few in both sexes; 4 out of 197 (2.0%) in males and 8 of 316 (2.5%) in females. The distance moved between sequential trapping periods was similar for males and females; the mean being 10.2 m and 9.0 m respectively. Both males and females moved larger distances during the breeding season than during the nonbreeding period. The distance moved between sequential trapping periods showed a strong negative relation to density, i.e. both sexes moved shorter distances at higher densities, but there were no differences between periods of increasing and declining population densities. These results contradict the dispersal predictions of all major hypotheses proposed to explain population fluctuations in small mammals. The dispersal patterns fit a geometric distribution, suggesting that competition is the primary factor determining the dispersal characteristics of this population.     

Spatial pattern of seedlings 1 year after fire in a Mediterranean pine forest

Summary The spatial distribution of seedlings of the dominant perennial plant species (Pinus halepensis, Cistus salviifolius, Rhus coriaria) and may annual species was studied after a wild fire in an eastern Mediterranean pine forest. The spatial distribution of all seedlings is affected by the location of the old burned pine trees. Seedling density of Pinus and Cistus is higher at a distance from the burned pine canopy and lower near the burned pine trunk. It is also higher beneath small burned pine trees than under big ones. Rhus seedling density is higher under big burned pine trees and also near the burned trunks. Seedlings of Pinus, Cistus and Rhus growing under the burned canopy of big pine trees tend to be taller than seedlings under small ones or outside the burned canopy. Most annual species germinate and establish themselves outside the burned canopies, and only a few annual species are found beneath them. It is suggested that variation in the heat of the fire, in the amount of ash between burned pine trees of different sizes, and in the distance from the burned canopy are responsible for the observed pattern of seedling distribution. The possible ecological significance of the spatial pattern of seedlings distribution and their differential growth rate are discussed.     

Initiation of early breeding in a population of Microtus townsendii (Rodentia) with the secondary plant compound 6-MBOA

Summary Feeding the secondary plant compound 6-Methoxybenzoxazolinone (6-MBOA) during winter to a free living population of Microtus townsendii accelerated breeding in females. Both the recruitment of young and sexual maturation of these young were advanced by four weeks in comparison with a control population. Overwintered females supplied with 6-MBOA matured at a lower body weight than control females. But there was no such weightat-maturity difference between the grids for males. During April and May 72% of all juveniles captured came from the experimental population. Winter reproduction and early recruitment of young stimulated by 6-MBOA could have important population consequences for these voles.     

Mating system of the meadow vole, Microtus pennsylvanicus

Previous studies on parental and spacing behavior of Microtuspennsylvanicus suggest a promiscuous mating system, but attemptsto find multiple paternity in single litters have been unsuccessful.In this paper we present evidence of multiple paternity in singlelitters conceived in the wild early in the breeding season.The proportion of litters sired by multiple males was estimated,by a conservative method, to be 33.1%.We argue that the presenceof promiscuity, rather than polygyny, in M. pennsylvanicus isthe result of two factors. First, overwintered breeding malesare similar in age and size, resulting in small variation incompetitive ability among males. This reduced variation in competitiveability reduces the possibility that some males defend severalfemales and others defend none. Second, the habitat structureof the meadow vole makes it difficult for a male to detect othermales nearby, and this reduces the possibility that one maleexcludes others from mating when a female comes into estrus.     

Demography of the western harvest mouse,Reithrodontomys megalotis,in eastern Kansas

Summary Reithrodontomys megalotis was live-trapped on three open field grids in eastern Kansas from August 1979 to August 1982. One grid was a control on which normal demography was monitored, and two were experimental grids where periodic removal of residents allowed the investigation of the demographic and fitness consequences of emigration. Popullations on the control grid showed an annual cycle in numbers, reaching peaks in density during the winter of each year, falling to low densities during the summer. Low summer densities were attributed, at least partially, to low trappability of R. megalotis during periods of high resource abundance. Reproduction was initiated in the spring of each year at approximately the same time as the emergence of new vegetative growth, and ceased in late fall of each year. The trappable population was composed almost entirely of adults, and the sex ratio was skewed significantly toward females. A statistically significant negative association between the number of M. ochrogaster residents and the reproductive activity of female R. megalotis residents was found. A canonical correlation analysis revealed a common seasonal component to the demography of the two species, and possible interspecific affects. Emigrating R. megalotis were a nonrandom sample of the population, with emigrants more likely to be subadult and juvenile males when compared to residents. No association was detected between the numbers of M. ochrogaster colonizing the removal grid and the numbers of R. megalotis colonizing the same removal grid, or between the number of M. ochrogaster residents on the control grid and the numbers of R. megalotis colonizing the removal grids. However, the number of R. megalotis residents on the control grid is positively correlated with the number of R. megalotis on the removal grids.     

Isolation and characterization of polymorphic microsatellite loci in the field vole,Microtus agrestis,and their cross‐utility in the common vole,Microtus arvalis

We developed nine polymorphic microsatellite loci for the field vole, Microtus agrestis. The number of alleles ranged from five to 15 and observed heterozygosities ranged from 0.40 to 1.00. We also tested the microsatellite loci for amplification and polymorphism in the congeneric species Microtus arvalis. Five of the nine loci were successfully analysed in this species. The microsatellite markers will be employed in studies of reproductive success and fine‐scale spatial genetic structure.     

Regulation of vole populations by the nematode <Emphasis Type="Italic">Trichuris arvicolae</Emphasis>: insights from modelling

The goal of this study is to determine whether a parasitic nematode may regulate, or destabilise by inducing demographic cycles, its host populations. We explore three host–parasite systems through population dynamic models. The hosts considered are the fossorial water vole, Arvicola terrestris, the common vole Microtus arvalis and the bank vole Myodes (Clethrionomys) glareolus and the parasitic nematode is Trichuris arvicolae. Three differential equation-based mathematical models are developed including host immunity and the existence of trade-off between immunity and host survival. Using parameters estimated from field data and laboratory observations, all these models show that T. arvicolae can induce host population regulation but not demographic cycles. The regulation effect of the nematode is un-ambiguous for the water vole (reduction of 50.2% of the host population size), but less obvious for the common vole (5.9%) and even less for the bank vole (1.4%). Important biological parameters to be taken into account in such models are discussed. Experimental confirmation of the regulatory potential of the nematode and of the costs of mounting an immune response against this nematode are now required. Communicated by W. Lutz     

Population dynamics of the collared lemming and the tundra vole at Pearce Point,Northwest Territories,Canada

From 1987 to 1989 we monitored population changes during summer of the collared lemming (Dicrostonyx groenlandicus) and the tundra vole (Microtus oeconomus) at Pearce Point, Northwest Territories, Canada (69° 48 N, 122° 40 W). Populations on four study areas did not cycle but remained at low density (<3/ha) each year and continued at low numbers for the following 3 years (Reid et al. 1995). Lemming numbers often declined throghout the summer in spite of continous reproduction, and population recovery occurred overwinter. Heavy predation losses of radio-collared lemmings occurred each summer and this lemming population may be trapped in a predator-pit. Collared lemmings breed in winter and only because of winter population growth do these populations persist. Tundra vole numbers increased rapidly in most summers but usually declined overwinter. Tundra voles do not seem able to sustain winter reproduction in this extreme environment and this prevents them from reaching high density because of the short summer. Population growth in both these rodents could be prevented by poor food or by predation losses, and landscape patchiness may also help to prevent population growth. For lemmings we do not think that a shortage of shelter or intrinsic limitations could be restricting population increase at Pearce Point. This is the first detailed study of a non-cyclic collared lemming population.     

Consumption of grass endophytes alters the ultraviolet spectrum of vole urine

Fungal endophytes of grasses are known to benefit their hosts directly by increasing resistance to herbivores through mycotoxins. We propose and test assumptions of a novel hypothesis according to which fungal endophytes of grasses may benefit their hosts also indirectly by increasing the conspicuousness of a mammalian herbivore, the field vole (Microtus agrestis), to its avian predators by enhancing the ultraviolet visibility of vole urine. We found that field voles feeding on endophyte-infected meadow ryegrass (Lolium pratense) lost body mass, while voles feeding on non-infected meadow ryegrass gained mass. More interestingly, the maximum peak intensity of ultraviolet fluorescence in the urine of voles feeding on endophyte-infected grass shifted from over 380 nm to circa 370 nm, which is the suggested maximum sensitivity of the ultraviolet pigments in the eyes of vole-eating raptors. Therefore, grazing on endophyte-infected grass alters the ultraviolet spectrum of vole urine, thus potentially enhancing its visibility to avian predators.     

Molecular phylogeny of the speciose vole genus Microtus (Arvicolinae, Rodentia) inferred from mitochondrial DNA sequences

Voles of the genus Microtus represent one of the most speciose mammalian genera in the Holarctic. We established a molecular phylogeny for Microtus to resolve contentious issues of systematic relationships and evolutionary history in this genus. A total of 81 specimens representing ten Microtus species endemic to Europe as well as eight Eurasian, six Asian and one Holarctic species were sequenced for the entire cytochrome b gene (1140 bp). A further 25 sequences were retrieved from GenBank, providing data on an additional 23, mainly Nearctic, Microtus species. Phylogenetic analysis of these 48 species generated four well-supported monophyletic lineages. The genus Chionomys, snow voles, formed a distinct and well-supported lineage separate from the genus Microtus. The subgenus Microtus formed the strongest supported lineage with two sublineages displaying a close relationship between the arvalis species group (common voles) and the socialis species group (social voles). Monophyly of the Palearctic pitymyid voles, subgenus Terricola, was supported, and this subgenus was also subdivided into two monophyletic species groups. Together, these groupings clarify long-standing taxonomic uncertainties in Microtus. In addition, the "Asian" and the Nearctic lineages reported previously were identified although the latter group was not supported. However, relationships among the main Microtus branches were not resolved, suggesting a rapid and potentially simultaneous radiation of a widespread ancestor early in the history of the genus. This and subsequent radiations discernible in the cytochrome b phylogeny, show the considerable potential of Microtus for analysis of historical and ecological determinants of speciation in small mammals. It is evident that speciation is an ongoing process in the genus and that the molecular data provides a vital insight into current species limits as well as cladogenic events of the past.     

Polymorphic microsatellite loci and PCR multiplexing in the common vole,Microtus arvalis

We isolated and characterized 14 dinucleotide microsatellite loci in the common vole Microtus arvalis (Palas). Two multiplex panels both comprising seven loci were developed. Application to a set of 21 individuals allowed clear and easy characterization of allele sizes except for two loci which were then withdrawn from further analyses. The number of alleles ranged from four to 19 per locus with the observed heterozygosity ranging from 0.55 to 0.95. These sets of microsatellite loci provide high throughput capacity for population genetic studies at a minimum cost.