predation pressure by avian predators suggests summer limitation of small-mammal populations in the canadian arctic.predation has been suggested to be especially important in simple food webs and less productive ecosystems such as the arctic tundra, but very few data are available to evaluate this hypothesis. we examined the hypothesis that avian predators could drive the population dynamics of two cyclic lemming species in the canadian arctic. a dense and diverse suite of predatory birds, including the snowy owl (bubo scandiacus), the rough-legged hawk (buteo lagopus), and the long-tailed jaeger (stercorariu ...201424649646
highly overlapping winter diet in two sympatric lemming species revealed by dna metabarcoding.sympatric species are expected to minimize competition by partitioning resources, especially when these are limited. herbivores inhabiting the high arctic in winter are a prime example of a situation where food availability is anticipated to be low, and thus reduced diet overlap is expected. we present here the first assessment of diet overlap of high arctic lemmings during winter based on dna metabarcoding of feces. in contrast to previous analyses based on microhistology, we found that the die ...201525635852
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 r ...199528306997
a male-biased natal sex-ratio in inbred collared lemmings, dicrostonyx groenlandicus.a captive colony of collared lemmings (dicrostonyx groenlandicus) from northern alaska produced a male-biased sex ratio of 67% males for about three generations. these lemmings have a pair of autosomes fused to the sex chromosomes. thus, males have two copies of some (formerly autosomal) sex-linked genes: one set is x-linked; the other can be described as y-linked. given such a karyotype, deleterious recessive alleles on the autosomal portion of the x chromosome are more resistant to selection t ...19958598343
effect of photoperiod, testosterone, and estradiol on body mass, bifid claw size, and pelage color in collared lemmings (dicrostonyx groenlandicus).collared lemmings undergo several photoperiod-mediated seasonal physiological changes. when exposed to short photoperiod, lemmings increase in size, develop a bifid claw, and molt to a white pelage. previous data indicate that body mass, claw size, and pelage color are influenced by hormones of testicular origin, suggesting that, on a seasonal basis, changes in production of, or sensitivity to, testicular hormones may play a role in the development of the phenotype characteristic of the ambient ...19948194745
resource partitioning by mammalian herbivores in the high arctic.willow (salix arctica) and sedges (carex stans and eriophorum triste) were the dominant plants available as forage for herbivores in the high arctic of greenland. willow leaves were of high quality as forage in early stages, of phenology, but crude protein and digestibility declined markedly by late stages whereas sedges, remained high in forage quality throughout the growing season. densities of fecal pellets indicated that muskoxen (ovibos moschatus) made heaviest use of sedge-dominated vegeta ...199428313731
pre- and postnatal effects of photoperiod on collared lemmings (dicrostonyx groenlandicus).we investigated the hypothesis that photoperiod information received during the prenatal and/or early postnatal periods influences subsequent development in collared lemmings. pregnant lemmings were exposed to either a short [8:16-h light-dark cycle (8:16)] or long (22:2) photoperiod throughout gestation. on the day of birth, pups were cross-fostered to dams housed in either short or long photoperiod. after an 11-day experimental lactational period (lact), all animals were transferred to an inte ...19947943428
response of collared lemmings to melatonin: ii. infusions and photoperiod.collared lemmings (dicrostonyx groenlandicus) show much phenotypic plasticity when exposed to photoperiods of varying length. in addition to "long day" and "short day" morphologies, apparent when animals are exposed to 22l:2d and 8l:16d, respectively, animals with intermediate features appear when collared lemmings are placed on day lengths ranging from 18l:6d to 14l:10d. body mass, body composition, pelage color and length, the presence and size of a bifid claw, and reproductive condition are a ...19947722868
cytogenetics of collared lemmings (dicrostonyx groenlandicus). i. meiotic behavior and evolution of the neo-xy sex-chromosome system.electron-microscopic analysis of surface-spread synaptonemal complexes at pachynema and light-microscopic analysis of chromosomal configurations at diakinesis/metaphase i corroborate the hypothesized neo-xy derivation of the sex chromosomes of dicrostonyx groenlandicus. although an intact neo-xy pairing configuration was observed in a relatively small percentage of the pachytene cells in each individual, the high incidence of neo-xy bivalents at diakinesis/metaphase i suggests that the other obs ...19979605875
alteration of testicular response to long photoperiod by transient exposure to short photoperiod in collared lemmings (dicrostonyx groenlandicus).the reproductive response of collared lemmings (dicrostonyx groenlandicus) to photoperiod is unique for rodents. whereas most reproductively photoresponsive rodents show maximal gonadal growth when exposed to long photoperiod (long day), collared lemmings show delayed maturation when born and maintained under this condition. however, transfer of lemmings from short photoperiod (short day) to long day results in maximal gonadal growth, indicating that the response to long day depends upon photope ...19979155735
spontaneous testicular regression in collared lemmings (dicrostonyx groenlandicus) exposed to prolonged long photoperiod.reproductive maturation and attainment of maximal gonadal size in collared lemmings (dicrostonyx groenlandicus) is facilitated by transfer from a short photoperiod (8 h light: 16 h dark) to a long photoperiod (22 h light:2 h dark). however, reproductive maturation in lemmings born in 22 h light:2 h dark is impeded by exposure to the natal photoperiod of 22 h light:2 h dark. data from adult lemmings suggest that prolonged exposure to a long photoperiod of 20 h light:4 h dark results in gonadal re ...19989861171
cytogenetics of collared lemmings (dicrostonyx groenlandicus). ii. meiotic behavior of b chromosomes suggests a y-chromosome origin of supernumerary chromosomes.the patterns of synapsis and chiasma formation of the b chromosomes of male collared lemmings (dicrostonyx groenlandicus) were analyzed by light and electron microscopy and compared to expectations for various hypotheses for the intragenomic origin of supernumerary chromosomes. pachytene analysis revealed a variety of synaptic configurations including b-chromosome univalents, bivalents and trivalents. in approximately one-half of the pachytene nuclei examined, b chromosomes were in synaptic asso ...200111978976
infanticide and pregnancy failure: reproductive strategies in the female collared lemming (dicrostonyx groenlandicus). 19807378528
body composition in a seasonal model of obesity: longitudinal measures and validation of dxa.collared lemmings, dicrostonyx groenlandicus, show rapid changes in body mass on a seasonal basis. the objective of this study was to measure longitudinal changes in body composition in animals undergoing photoperiod-induced weight gain and loss using dxa.200212429883
photoperiod differentially affects immune function and reproduction in collared lemmings (dicrostonyx groenlandicus).many nontropical rodent species experience predictable annual variation in resource availability and environmental conditions. individuals of many animal species engage in energetically expensive processes such as breeding during the spring and summer but bias investment toward processes that promote survival such as immune function during the winter. generally, the suite of responses associated with the changing seasons can be induced by manipulating day length (photoperiod). collared lemmings ...200616998158
photoperiod alters affective responses in collared lemmings.this study examined photoperiodic regulation of affective behaviours in collared lemmings (dicrostonyx groenlandicus). male and female lemmings were housed in either long (ld 22:2), intermediate (ld 16:8), or short days (ld 8:16) for 9 weeks. exposure to short days induced moult to a winter pelage and gonadal regression in male, but not female, lemmings. lemmings housed in long days reduced anxiety-like responses in the elevated plus maze. depressive-like behaviours were decreased in the interme ...200717339057
the behavioral and somatic effects of ovariectomy and replacement therapy in female collared lemmings (dicrostonyx groenlandicus).the effects of ovariectomy with or without supplementary treatment with estradiol benzoate (eb) and progesterone on reproductive behavior and organ weights were studied in adult lemmings. the sex behavior of intact diestrous and untreated castrated females was similar, and both groups behaved differently from intact estrous females in terms of scores for lordosis and mounting behavior. as little as a daily .1 mcg dose of eb induced receptivity in some females within 3 days and in 83% of the fema ...1976945225
the influence of exteroceptive factors on the estrous cycle of the collared lemming (dicrostonyx groenlandicus). 19751240772
prolonging the arctic pulse: long-term exploitation of cached eggs by arctic foxes when lemmings are scarce.1. many ecosystems are characterized by pulses of dramatically higher than normal levels of foods (pulsed resources) to which animals often respond by caching foods for future use. however, the extent to which animals use cached foods and how this varies in relation to fluctuations in other foods is poorly understood in most animals. 2. arctic foxes alopex lagopus (l.) cache thousands of eggs annually at large goose colonies where eggs are often superabundant during the nesting period by geese. ...200717714265
landscapes of fear or competition? predation did not alter habitat choice by arctic systems where predation plays a key role in the dynamics of prey populations, such as in arctic rodents, it is reasonable to assume that differential patterns of habitat use by prey species represent adaptive responses to spatial variation in predation. however, habitat selection by collared (dicrostonyx groenlandicus) and brown (lemmus trimucronatus) lemmings depends on intra- and inter-specific densities, and there has been little agreement on the respective influences of food abundance, pr ...201424100757
morphological changes in the ovaries and other organs of the collared lemming (dicrostonyx groenlandicus) during pregnancy and pseudopregnancy. 19751116061
ovulation and related phenomena in the collared lemming (dicrostonyx groenlandicus).ovulation of the collared lemming occurred approximately 9 hours after copulation or injection of hcg. during long periods of estrus, ovulation did not occur spontaneously, but was induced by copulation during estrus. induction of ovulation was independent of the time of day at which copulation occurred. between the time of copulation and 8 hours later, preovulatory follicles increased in size. following copulation, meiotic changes in the ova of preovulatory follicles proceeded rapidly and 1 hou ...19744601603
mammary gland tumors in collared lemmings (dicrostonyx groenlandicus). 19724338716
behavioural biology of the collared lemming dicrostonyx groenlandicus (traill): i. agonistic behaviour. 20045691848
behavioural biology of the collared lemming dicrostonyx groenlandicus (traill): ii. sexual behaviour. 20065674231
spontaneous activity of the lemming dicrostonyx groenlandicus richardsoni merriam as indicated in 24-hour records of oxygen consumption. 195713513673
benefiting from a migratory prey: spatio-temporal patterns in allochthonous subsidization of an arctic predator.1. flows of nutrients and energy across ecosystem boundaries have the potential to subsidize consumer populations and modify the dynamics of food webs, but how spatio-temporal variations in autochthonous and allochthonous resources affect consumers' subsidization remains largely unexplored. 2. we studied spatio-temporal patterns in the allochthonous subsidization of a predator living in a relatively simple ecosystem. we worked on bylot island (nunavut, canada), where arctic foxes (vulpes lagopus ...201222268371
cycles and synchrony in the collared lemming (dicrostonyx groenlandicus) in arctic north america.lemming populations are generally characterised by their cyclic nature, yet empirical data to support this are lacking for most species, largely because of the time and expense necessary to collect long-term population data. in this study we use the relative frequency of yearly willow scarring by lemmings as an index of lemming abundance, allowing us to plot population changes over a 34-year period. scars were collected from 18 sites in arctic north america separated by 2-1,647 km to investigate ...200128547620
habitat selection, reproduction and predation of wintering lemmings in the arctic.snow cover has dramatic effects on the structure and functioning of arctic ecosystems in winter. in the tundra, the subnivean space is the primary habitat of wintering small mammals and may be critical for their survival and reproduction. we have investigated the effects of snow cover and habitat features on the distributions of collared lemming (dicrostonyx groenlandicus) and brown lemming (lemmus trimucronatus) winter nests, as well as on their probabilities of reproduction and predation by st ...201121701915
catechin content and consumption ratio of the collared lemming.chemical- plant defences as mechanisms affecting herbivore populations have been debated during the past decade. several authors have questioned the hypothesis, but the present study shows that collared lemmings ( dicrostonyx groenlandicus) in northeast greenland prefer food plants with a lower catechin content. dicrostonyx species are known to have specialised on shrubs, especially dryas spp. and salix spp., rather than graminoids like other related microtines. bioassays were conducted using fo ...200312698346
multiple glacial refugia in the north american arctic: inference from phylogeography of the collared lemming (dicrostonyx groenlandicus).cryptic northern refugia beyond the ice limit of the pleistocene glaciations may have had significant influence on the current pattern of biodiversity in arctic regions. in order to evaluate whether northern glacial refugia existed in the canadian arctic, we examined mitochondrial dna phylogeography in the northernmost species of rodents, the collared lemming (dicrostonyx groenlandicus) sampled across its range of distribution in the north american arctic and greenland. the division of the colla ...200212396480
metabolic rate and thermal conductance of lemmings from high-arctic canada and siberia.the arctic climate places high demands on the energy metabolism of its inhabitants. we measured resting (rmr) and basal metabolic rates (bmr), body temperatures, and dry and wet thermal conductances in summer morphs of the lemmings dicrostonyx groenlandicus and lemmus trimucronatus in arctic canada, and the bmr of d. torquatus, d. groenlandicus, l. sibiricus, l. bungei and l. trimucronatus in siberia. in contrast to previous studies the data were collected on animals that had spent only a limite ...200212122453
safety of lyophilized sag2 oral rabies vaccine in collared lemmings.fifteen collared lemmings (dicrostonyx groenlandicus) were exposed to a lyophilized oral rabies vaccine designed to immunize wild carnivore populations. no animals contracted rabies from the vaccine as determined by the absence of clinical signs after 37 days and lack of rabies virus in brain tissue determined by the fluorescent antibody (fa) test. these results suggest that collared lemmings would not contract rabies if they ingested this lyophilized vaccine in the wild during bait vaccination ...200211838220
spatial structure of lemming populations (dicrostonyx groenlandicus) fluctuating in density.the pattern and scale of the genetic structure of populations provides valuable information for the understanding of the spatial ecology of populations, including the spatial aspects of density fluctuations. in the present paper, the genetic structure of periodically fluctuating lemmings (dicrostonyx groenlandicus) in the canadian arctic was analysed using mitochondrial dna (mtdna) control region sequences and four nuclear microsatellite loci. low genetic variability was found in mtdna, while mi ...200111298962
phylogeography and mitochondrial dna (mtdna) diversity in north american collared lemmings (dicrostonyx groenlandicus).variation in the nucleotide sequence of the mitochondrial control region (250 bp) and the cytochrome b region (870 bp) was examined in collared lemmings (dicrostonyx groenlandicus) from 19 localities in northern alaska and the canadian arctic. the division of d. groenlandicus in two phylogeographical groups with limited divergence across the mackenzie river is consistent with the separation of this species in more than one refugial area located to the northwest of the laurentide ice sheet during ...200010736030
influence of photoperiod, time, and sex on hormone concentrations in collared lemmings (dicrostonyx groenlandicus).collared lemmings (dicrostonyx groenlandicus) of both sexes show seasonal changes in body mass and body composition. previous studies using single-point sampling indicated that, in young males, these photoperiod-mediated changes are associated with changes in circulating growth hormone (gh), corticosterone (b), and thyroid hormones. the present study was conducted to (1) examine daily fluctuations in serum levels of gh, b, and thyroxine (t4) in animals exposed to long (22l:2d, "ld"), intermediat ...19968713644
development of pelodera strongyloides (schneider, 1860) schneider, 1866 (nematoda: rhabditidae) in culture.dauerlarvae of pelodera strongyloides, recovered from two species of lemmings, dicrostonyx groenlandicus (traill) and lemmus trimucronatus (richardson) trapped at eskimo point, n.w.t, were cultured on agar medium with e. coli. development from egg to adult stage was followed. eggs hatched between 22 and 26 hours at 22 degrees c. the first moult occurred 24 to 28 hours after the eggs hatched, the second at 40 to 48 hours, the third at 60 to 64 hours and the fourth at 84 to 88 hours at 22 degrees ...19807190984
spontaneous gastric squamous cell carcinomas and other neoplasms in greenland collared lemmings (dicrostonyx groenlandicus).malignant neoplasms were present in 39/66 dicrostonyx groenlandicus of varying ages, examined from a laboratory colony. the presence of multiple neoplasms in some resulted in an overall average of 1.15 tumors/affected animal. gastric squamous papillomas were present in nine, and locally invasive or metastatic gastric squamous cell carcinomas in a further 36 animals. three mammary adenocarcinomas, one pancreatic islet cell tumor, one probable pancreatic adenocarcinoma and one adrenal cortical ade ...19826751508
social olfaction in male brown lemmings (lemmus sibiricus = trimucronatus) and collared lemmings (dicrostonyx groenlandicus): i. discrimination of species, sex, and estrous condition.when tested in a y-maze olfactometer, sexually experienced and sexually naive brown and collared lemmings (lemmus sibiricus = trimucronatus and dicrostonyx groenlandicus) preferred the odor of conspecific females to the odor of females of another species. both experienced and naive males also preferred the odor of conspecific females to that of conspecific males. only sexually experienced males showed a significant preference for estrous over nonestrous conspecific females. sexually experienced ...19846368118
development of collared lemmings, dicrostonyx groenlandicus, is influenced by pre- and postweaning photoperiods.we examined the role of pre- and postweaning photoperiod on postweaning development of collared lemmings. lemmings were gestated and reared to weaning (19 days of age) in one of three photoperiods: 22l:2d (22 hr of light:2 hr of dark), 16l:8d, and 8l:16d. at weaning, lemmings were either maintained in their natal photoperiod or transferred to one of the other two photoperiods. at the termination of the experiment (10 weeks postweaning) data were collected on somatic characters (body weight, bifi ...19938263467
threshold photoperiods for the induction of short day traits in collared lemmings (dicrostonyx groenlandicus).when exposed to short photoperiod collared lemmings undergo a number of physiological and morphological changes including an increase in body weight, a change in body composition, development and enlargement of the bifid "digging" claw, and a molt to a white winter pelage. we investigated the threshold photoperiods for the induction of these traits in male and female lemmings born and raised under a 22l:2d photoperiod and transferred at weaning (19 days of age) to various other photoperiods. mal ...19938376952
role of prolactin and the gonads in seasonal physiological changes in the collared lemming (dicrostonyx groenlandicus).on a seasonal basis, collared lemmings undergo a number of physiological and morphological changes. short photoperiod exposure results in a molt to a white pelage, an increase in body weight, a reduction in relative body fat content, an increase in relative water content, and the development of a bifid claw. treatment with the dopamine agonist, cb-154, resulted in a reduction in serum prolactin and the development of the white pelage in lemmings housed under 16l:8d, while treatment with the dopa ...19938501441
role of photoperiod in reproductive maturation and peripubertal hormone concentrations in male collared lemmings (dicrostonyx groenlandicus).onset of sexual maturation was determined in weanling male collared lemmings exposed to one of three experimental regimens of different photoperiods before and after weaning. animals gestated in photoperiods of either 16 h light:8 h dark or 8 h light:16 h dark. those from 16 h light:8 h dark were transferred at 19 days of age to either 20 h light:4 h dark or 8 h light:16 h dark; those gestated under 8 h light: 16 h dark remained in that photoperiod throughout the experiment. after exposure for 1 ...19921432946
thermoregulation, growth, and reproduction in alaskan collared lemmings: role of short day and assess factors controlling seasonal thermoregulatory and reproductive changes, collared lemmings (dicrostonyx groenlandicus) were exposed for 16 wk to long day (ld, 22 h light: 2 h dark) and warm (15 +/- 3 degrees c), ld and cold (1 +/- 0.5 degrees c), short day (sd, 4 h light: 20 h dark) and warm, sd and cold or acclimatized to outdoor winter conditions (out). hair length and color, body mass, and food intake were monitored weekly. resting metabolic rates (rmr) and nonshivering thermogenesis ...19911887941
failure of strange females to cause pregnancy block in collared lemmings, dicrostonyx groenlandicus.the effects of exposure to unfamiliar females on pregnancy success of recently mated females were examined in collared lemmings (dicrostonyx groenlandicus). four days after mating, females in their home cage were exposed to strange, female intruders that were either nonpregnant or 16 days pregnant. other recently mated females were introduced to the home cage of 16-day-pregnant females. pregnancy success of the recently mated females was not reduced in any of these treatments. in the paired enco ...19853910021
social olfaction in male brown lemmings (lemmus sibiricus = trimucronatus) and collared lemmings (dicrostonyx groenlandicus): ii. discrimination of mated and unmated females.when tested in a y-maze olfactometer, male brown and collared lemmings (lemmus sibiricus = trimucronatus and dicrostonyx groenlandicus) preferred the odor of unmated receptive females to the odor of females with which they had just copulated. similarly, sexually satiated males preferred the odor of an unmated receptive female to that of a strange female that had recently copulated with another male. sexually experienced males without recent copulatory experience also demonstrated this preference ...19846368119
quantitative morphology and environmental responses of the pineal gland in the collared lemming (dicrostonyx groenlandicus).collared lemmings from churchill, manitoba, and their descendants were studied in captivity to define neuroendocrine and related histophsiological characteristics and responses, particularly in relation to photic and temperature conditions. relatively great pineal size (0.1755 +/- 0.0167 mm3, or 3.08 +/- 0.30 = pineal volume in mm3 x 10(3)/body weight in gm; n = 16) shown in this arctic rodent is consistent with the suggestion that pineal size and significance may tend to be greater in more nort ...1978727154
the effects of social rank on reproductive indices in groups of male collared lemmings (dicrostonyx groenlandicus). 1978630030
the influence of photoperiod on growth and sexual function in male and female collared lemmings (dicrostonyx groenlandicus).the effect of photoperiod on sexual function and growth in weanling male and female collared lemmings (dicrostonyx groenlandicus) was studied. males and females maintained in 6 hr light:18 hr dark after weaning were larger at the end of 70 days than their siblings kept in 20l:4d. males in 6l:18d were longer and overall body growth was greater. males in 6l:18d had heavier adrenals but there were no differences in the weights of testes, preputial glands or seminal vesicles or in the mean testoster ...19761255561
reproductive performance and growth in captive collared lemmings (dicrostonyx groenlandicus). 19751139465
the influence of mature males on sexual maturation in female collared lemmings (dicrostonyx groenlandicus). 19751123824
complete mitochondrial genomes of the north american collared lemmings dicrostonyx groenlandicus traill, 1823 and dicrostonyx hudsonius pallas, 1778 (rodentia: arvicolinae).the complete mitochondrial genomes of two species of the north american collared lemmings were obtained by using pcr amplification and capillary sequencing (genbank accession nos. kx712239 and kx683880). the collared lemming mitochondrial genomes are 16,341 and 16,338 base pairs long and show the gene order, contents and gene strand asymmetry typical for mammals. the mitogenome sequences provide an important genomic resource for the collared lemmings, which are model study species in arctic gene ...201628642935
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