Hematology of the Norwegian Lemming (Lemmus lemmus(L.))

Basic hematological parameters of laboratory-reared Lemmus lemmus have been investigated. The results have been summarized together with those from ten other species of microtine rodents. Climatic conditions, especially the microclimate of the subnivean air space, have been considered to offer possible explanations for the higher values in L. trimucronatus compared to L. Lemmus.     

The myology of the manus of microtine rodents

A study of the muscles of the manus of 13 genera and subgenera of microtine rodents revealed considerable variation which could be organized into 23 primitive-derived evolutionary hypotheses (transmutation series). The results, when compared with those for other mammals, produced functional/ecological hypotheses which were tested by comparing their predictions with the literature. The microtine manus is morphologically distinguished by nine characters and is adapted for a terrestrial/semi-fossorial niche. In particular, Dicrostonyx and Lemmus (distinguished by eight characters) possess the most highly fossorial manus, while the manus of Arborimus (distinguished by eight characters) contains a combination of primitive characters and derived characters which give the Tree vole the most highly developed 'clasping' ability among the microtines studied. The study has revealed characters which have potential systematic value but it is probable that parallelism has occurred in the microtine manus. When the manual characters are combined with characters from other functional complexes, their systematic value can be more clearly determined.     

A comparison of the tryptic peptides of hemoglobin from two cricetine genera: Peromyscus and Calomys

The composition of tryptic peptides was determined for the major hemoglobin from two cricetine rodents. Peromyscus maniculatus bairdii and Calomys callosus. Amino acid sequences are proposed from homologous alignment with the respective sequences of white mouse and a microtine ‘stem’ developed from previous studies. These two hemoglobins differed at 11 - and 17 β-positions, showing only one common position beyond the cricetid stems (Hesperomyini, Cricetinae) and only three common positions with the microtinae beyond the muroid or myomorph stem (Cricetidae).     

Densities of microtime rodents along a pollution gradient from a copper-nickel smelter

Population densities of microtine rodents were studied along an air pollution gradient in the Kola Peninsula, Russia, by long-term and short-term trapping. The study area is affected by high sulphur dioxide and heavy metal emissions from the Severonikel copper-nickel smelter in Monchegorsk. The density of Clethrionomys rufocanus, the most abundant vole species in the area, was lowest close to the smelter and increased with distance up to the farthest, less polluted trapping sites. Clethrionomys glareolus, C. rutilus and Lemmus lemmus were absent from the most severely damaged area and were also scarce at the moderately polluted area 28 km south of the smelter. Although the population of C. glareolus has previously been cyclic at the moderately polluted area, we were unable to demonstrate any regular cycle. The most likely explanation for the low number of microtine rodents in the damaged and moderately polluted areas in a decrease in the quantity of important food plants: epiphytic lichens for C. glareolus and possibly C. rutilus, mosses for L. lemmus and seed plants, especially Vaccinium myrtillus, for C. rufocanus. Close to the smelter, direct toxic effects of heavy metals may also reduce population densities. The results show that pollutants may change the relative proportions of microtine species.     

Comparing the genetic population structure of two species of arctic lemmings: more local differentiation in Lemmus trimucronatus than in Dicrostonyx groenlandicus

Collared and brown lemmings ( Dicrostonyx groenlandicus and Lemmus trimucronatus ) are two largely sympatric and ecologically comparable species of arctic microtine rodents, differing however in some respects which allow us to hypothesise differences in the genetic structure of their populations. Collared lemmings are particularly well adapted to life at high latitude, they occasionally emerge to the surface of the snow and may disperse over larger distances than brown lemmings – possibly even over snow and ice. This should result in more local differentiation among populations of brown lemmings than among populations of collared lemmings. We compared the genetic population structure between the two lemming species in a fragmented landscape with small islands in the central Canadian Arctic using four microsatellite loci and partial mitochondrial control region sequences. Both types of genetic markers showed higher differentiation ( F _ST values) among local populations for brown lemmings than for collared lemmings. We discuss to what extent the observed genetic differences may be explained by differences in dispersal rates in addition to differences in average effective population size.     

Comparative solubilities and electrophoresis of microtine hemoglobins.

1. The electrophoretic mobilities of the hemoglobins of 7 taxa of microtines were compared. Microtus oeconomus, M. pennsylvanicus pullatus and M. xanthognatus showed identical 2-band patterns on electrophoresis of their hemoglobins while M. pennsylvanicus tananaensis showed only a single hemoglobin corresponding to the major band of the others. Dicrostonyx rubricatus and D. stevensoni exhibited identical patterns different from the Microtus species. Lemmus sibiricus had a slow hemoglobin component with mobility slightly different from the slow ones of the Microtus species while the fast component appeared the same. 2. Electrophoresis of individual globin chains from hemolysates, purified hemoglobins, and isolated chains indicated a large degree of similarity between the species studied, although there were significant differences in hemoglobin patterns. 3. The minor hemoglobin band in Microtus seems to be the result of a second alpha chain locus as determined from the hemoglobins from hybrids of two subspecies. 4. Salting-out studies indicated differences between hemoglobins that were not detectable by electrophoresis of either whole hemoglobins or isolated chains. 5. M. xanthognathus hemolysate was considerably less soluble than those of M. oeconomus and M. pennsylvanicus pullatus which had essentially the same solubility. 6. The major hemoglobin components of M. pennsylvanicus pullatus and M. xanthognathus were considerably less soluble than either the corresponding unfractionated hemolysates or purified minor components.     

Gyr Falcons, ptarmigan and microtine rodents in northern Sweden

A Gyr Falcon Falco rusticolus population in Northern Sweden (66°N, 17°E) was monitored from 1996 to 2002 in relation to its predator–prey interactions with its main and alternative prey species. Ptarmigan species Lagopus spp., and especially Rock Ptarmigan L. mutus , were the Gyr Falcons' most important prey and constituted more than 90% of the prey biomass. A 21-fold difference in ptarmigan abundance was found across Falcon breeding territories. However, this great variation in prey availability corresponded to only about a 10% shift in Gyr Falcon diet across territories, suggesting that the Falcons were reluctant or unable to compensate for declining ptarmigan availability by using alternative prey categories. Gyr Falcons did not respond functionally to microtine rodent abundance. Their diets were unaffected by a peak in the microtine rodent population cycle when Norwegian Lemmings Lemmus lemmus occurred in high numbers in the study area. Gyr Falcons responded numerically to their prey in two ways. First, there was a reproductive response with a significant relationship between the number of chicks fledged and the number of ptarmigan in the breeding territories. Secondly, although the Gyr Falcons did not utilize microtines as prey, there was a relationship between the microtine rodent abundance and the number of pairs that attempted to breed each year. This could be a result of an indirect community interaction, assuming that other predators switched from ptarmigan to microtines as prey, which could have had a positive effect on the breeding performance of the Gyr Falcons. The Gyr Falcons acted as true specialist predators, and their narrow food niche probably reflected a general lack of suitable alternative prey in the study area.     

Fay and Rausch 1969 revisited: Babesia microti in Alaskan small mammals

The Holarctic distribution of Babesia microti within small rodents implies an ancient association. A seminal report of piroplasms in Alaskan voles suggested to us the possibility that B. microti entered North America within Eurasian microtine rodents dispersing through Beringian corridors. To test this hypothesis, we analyzed samples from Alaskan rodents by polymerase chain reaction for evidence of infection with B. microti; one-third of the rodents were found to be infected. Sequence analysis of the 18S rDNA gene demonstrates that Alaskan B. microti comprises a clade that infects microtines in several sites across North America and is distinct from a clade that is zoonotic.     

Social organization of the voleClethrionomys rufocanus and its demographic and genetic consequences: A review

Recent findings on the relationship between social interaction and demographic process in the gray-sided voleClethrionomys rufocanus are reviewed with reference to the findings in other microtine rodents. Social behavior was particularly focused on spacing and dispersal, and their effects on population dynamics are discussed. Female territoriality can limit a population abundance as a density-dependent factor, although its regulatory effect is controversial. Female philopatry and male-biased dispersal should bring about the clumped distribution of female relatives and genetically random distribution of males during the breeding season. The sexual difference in dispersal patterns can contribute to the mating behavior of the vole; promiscuous mating and low frequency of incestuous mating. However, effects of social structure, including kinship, on reproduction and survival of individuals still remains to be clarified. Molecular markers may help to solve these issues and provide new field of population ecology in microtine rodents.     

几种害鼠血红蛋白型的研究

哺乳动物的蛋白质生化多态现象(biochemical polymorphism)是微观生态学和种群分子遗传学共同涉及的课题,国外已有多年的研究历史,积累了丰富的资料(Lush,1970)。产生多态性的原因,一般认为是自然因素选择平衡的结果(Hedrick等,1976)。     

Local variation in arctic fox abundance on Svalbard,Norway

Arctic fox (Alopex lagopus) numbers vary greatly, with cyclic fluctuations often associated with fluctuations in microtine rodents. However, in areas where small prey mammals are absent, such as Iceland and Svalbard, such cyclic fluctuations are lacking. Annual fluctuations in the density of the arctic fox population on the Brøggerhalvøya peninsula and Kongsfjorden region on Svalbard, Norway, were studied from 1990 to 2001 by using indices of fox abundance. All indices showed similar trends; fox numbers were low in 1990, increased until 1995 whereupon they decreased sharply, before increasing again and levelling off in 2001. Increasing numbers of foxes during the first part of the study paralleled increasing numbers of Svalbard reindeer (Rangifer tarandus platyrhynchus) carcasses in winter and increasing numbers of nesting barnacle geese (Branta leucopsis) in summer. This study shows that the number of arctic foxes varies greatly even in areas without fluctuating microtine rodents.     

Significant morphological but little molecular differences between Trypanosoma of rodents from Alaska

We examined blood smears of 173 rodents and 33 shrews captured at 4 sites in the Gates of the Arctic National Park, northern Alaska, in summer 2002. Trypanosoma spp. were detected in the plasma of 5 Microtus oeconomus, 4 Microtus miurus, and 1 Lemmus trimucronatus. The trypomastigote morphology from different individuals of M. oeconomus caught at the same site and of M. miurus from different sites varied significantly. The 4 DNA sequences obtained from the blood smear positive samples contained 2 different haplotypes very similar to each other and to that of Trypanosoma microti. Of possible vectors of blood parasites, the flea Amalaraeus dissimilis was collected from M. miurus.     

Diet, body condition, and reproduction of Eurasian pine martens Mantes martes during cycles in microtine density

Winter diet, body condition, growth, reproduction, and age structure of pine martens Martes martes were studied during cycles in microtine density in south-central Sweden. I analysed 398 scats collected in winters 1988 89 to 1996-97. and 483 carcasses from martens trapped in winters 1989-90 to 1992-93. Microtines were the single most frequent prey category in the winter diet, and the consumption of microtines was correlated with microtine density. In the absence of microtines. pine martens increased the relative consumption of some alternative prey, most notably hares. Among adults, total food consumption, body condition, and reproductive success did not follow microtine density. Among juveniles, there were indications of lower total food consumption, smaller fat deposits, and higher trapping vulnerability, and among juvenile females also of lower body growth, when microtines were scarce. The data were, however, not consistent in this respect. I suggest that pine martens in the southern boreal region do not suffer from food shortage at microtine lows, and accordingly, that the demography of pine martens is independent of microtine cycles.     

The stepwise mutation model: an experimental evaluation utilizing hemoglobin variants

The stepwise mutation model of Ohta and Kimura (1973) was proposed to explain patterns of genetic variability revealed by means of electrophoresis. The assumption that electrophoretic mobility was principally determined by unit changes in net molecular charge has been criticized by Johnson (1974, 1977). This assumption has been tested directly using hemoglobin. Twenty-seven human hemoglobin variants with known amino acid substitutions, and 26 nonhuman hemoglobins with known sequences were studied by starch gel electrophoresis. Of these hemoglobins, 60 to 70% had electrophoretic mobilities that could be predicted solely on the basis of net charge calculated from the amino acid composition alone, ignoring tertiary structure. Only four hemoglobins showed a mobility that was clearly different from an expected mobility calculated using only the net charge of the molecule. For the remaining 30% of hemoglobins studied, mobility was determined by a combination of net charge and other unidentified components, probably reflecting changes in ionization of some amino acid residues as a result of small alterations in tertiary structure due to the amino acid substitution in the variant. For the nonhuman hemoglobins, the deviation of a sample from its expected mobility increased with increasing amino acid divergence from human hemoglobin A.-It is concluded that the net electrostatic charge of a molecule is the principal determinant of electrophoretic mobility under the conditions studied. However, because of the significant deviation from strict stepwise mobility detected for 30 to 40% of the variants studied, it is further concluded that the infinite-allele model of Kimura and Crow (1964) or a "mixed model" such as that proposed by Li (1976) may be more appropriate than the stepwise mutation model for the analysis of much of the available electrophoretic data from natural populations.     

On the interaction between stabilizing social factors and destabilizing trophic factors in small rodent populations

Mathematical models are developed in order to analyze whether or not social factors, such as, for example, the “social fence” (J. B. Hestbeck, 1982, Oikos 39, 157–163) will stabilize population density: the dynamic interaction between social factors and (dynamic) trophic factors is analyzed. It is concluded that social factors such as the “social fence” tend to stabilize population density; hence, if density cycles (as, e.g., seen in many microtine rodents) are observed in nature, it seems reasonable to conclude that density cycles are driven by, for example, trophic interactions and not by social factors. It is suggested that the “social fence” may explain why so many populations including several microtine populations have fairly stable densities despite the ever-existing destabilizing trophic interactions. Contrary to what is implied by J. B. Hestbeck (1983, “A Mathematical Model of Population Regulation in Cyclic Mammals,” Lecture notes in biomathematics, Vol. 52, Springer-Verlag, Berlin/New York), the analysis presented in this paper demonstrates that seasonal environmental changes are not essential for the generation of regular density cycles. Seasonal changes may, however, be necessary for generating a microtine-like density cycle. Empirical information on microtine rodents relating to the “social fence hypothesis” is discussed.     

Qualitative analysis of a predator-prey system with limit cycles

Fairly regular multiannual microtine rodent cycles are observed in boreal Fennoscandia. In the southern parts of Fennoscandia these multiannual cycles are not observed. It has been proposed that these cycles may be stabilized by generalist predation in the south.We show that if the half-saturation of the generalist predators is high compared to the number of small rodents the cycles are likely to be stabilized by generalist predation as observed. We give examples showing that if the half-saturation of the generalist predators is low compared to the number of small rodents, then multiple equilibria and multiple limit cycles may occur as the generalist predator density increases.     

Dynamics of voles and small mustelids in the taiga landscape of northern Fennoscandia in relation to habitat quality

In the forests of northern Fennoscandia during the I980's, the dynamics of microtine rodents changed from multiannual high amplitude fluctuations (cycles) to, depending on species, fluctuations with a strong seasonal component or fluctuations with smaller amplitude and lower frequency. Microtine and predator data from the Pallasjarvi area, Finnish Lapland, suggest that this transition took place at different rates in different parts of the taiga landscape. Generally, densities in forest habitats have been primarily seasonal since 198S-86. In mesic spruce taiga and in drier forest habitats microtines had a prolonged peak in 1981-83 and a crash in 1984-83. At the timberline, however, microtine populations dropped from peak to low densities already in 1982-83 but the final crash did not occur until spring 1985. The synchronous decrease in microtines densities in all habitat types in 1984-85 coincided with increase in weasel activity. Activity of other carnivores was consistently high in mesic lowland habitats. The data support following three conjectures. 1) Periodic abundance of least weasels is crucial for sustained vole cycles. 2) Predominance of stoats and other generalist predators lead to less regular fluctuations with a strong seasonal component where density declines occur in autumn and early winter. 3) In barren tundra areas, the vegetation cannot sustain high densities of microtines and. consequently, predation is not a necessary condition for population crashes.     

Small mammals cycles in northern Europe: patterns and evidence for a maternal effect hypothesis

1. Voles undergo pronounced oscillations over periods of 3–5 years in northern Europe. A latitudinal gradient of cycle periods and amplitudes has been reported for Fennoscandia, with periods and amplitudes increasing towards northern latitudes.
2. This study formulates a discrete time model based on maternal effects to explain the density fluctuation patterns of microtine rodents. The phenotypic transmission of quality from mothers to offspring generates delayed density dependence, which produces cyclic behaviour in the model.
3. The dynamic patterns predicted by the maternal effect model agree with data. We conclude that the maternal effect hypothesis is a plausible, parsimonious explanation for vole-density cycles in northern Europe.     

Factors in the evolution of hemoglobin function.

The packaging of vertebrate blood hemoglobins within cells places subtle constraints on hemoglobin evolution. Since the concentration of hemoglobin is near the solubility limit a selective advantage should exist for a noncomplementary external topology of amino acid residues. Further, any change in charge on the protein should alter ion distribution across the cell membrane and so modify ion-sensitive oxygen transport. An efficient hemoglobin must not only combine readily with oxygen at prevailing environmental oxygen pressures, but must also release it at metabolically appropriate pressures. These adaptations frequently employ different strategies to achieve the same objective in different animals. Some hemoglobins have evolved special properties unrelated to the transport of oxygen to metabolizing tissues. Thus many teleost fish have hemoglobins that discharge much of their oxygen at low pH even at high oxygen pressures. This property appears to aid in filling the swim bladder with oxygen. The hemoglobins of elasmobranchs have evoked a unique resistance to urea as a consequence of the high urea content of their blood. Sometimes the functional adaptations of hemoglobins are achieved by multiple hemoglobins in the same cells. Often, however, different red cell populations with functionally unique hemoglobins arise sequentially during ontogeny.