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John R Speakman - One of the best experts on this subject based on the ideXlab platform.

  • the impact of experimentally elevated energy expenditure on oxidative stress and lifespan in the short tailed field vole Microtus Agrestis
    Proceedings of The Royal Society B: Biological Sciences, 2008
    Co-Authors: Colin Selman, Jane S Mclaren, Andrew Collins, Garry G Duthie, John R Speakman
    Abstract:

    Life-history theory assumes that animal life histories are a consequence of trade-offs between current activities and future reproductive performance or survival, because resource supply is limited. Empirical evidence for such trade-offs in the wild are common, yet investigations of the underlying mechanisms are rare. Life-history trade-offs may have both physiological and ecological mediated costs. One hypothesized physiological mechanism is that elevated energy metabolism may increase reactive oxygen species production, leading to somatic damage and thus compromising future survival. We investigated the impact of experimentally elevated energy expenditure on oxidative damage, protection and lifespan in short-tailed field voles (Microtus Agrestis) maintained in captivity to remove any confounding ecological factor effects. Energy expenditure was elevated via lifelong cold exposure (7±2°C), relative to siblings in the warm (22±2°C). No treatment effect on cumulative mortality risk was observed, with negligible effects on oxidative stress and antioxidant protection. These data suggest that in captive animals physiologically mediated costs on life history do not result from increased energy expenditure and consequent elevations in oxidative stress and reduced survival.

  • regulation of body mass and adiposity in the field vole Microtus Agrestis a model of leptin resistance
    Journal of Endocrinology, 2007
    Co-Authors: Elzbieta Krol, John R Speakman
    Abstract:

    Adult mammals are typically highly resistant to perturbations in their energy balance. In obese humans, however, this control appears to be lost. Apart from a few exceptional cases, this loss of control occurs despite appropriate levels of circulating leptin – suggesting that elevated adiposity may be a consequence of failure to respond to the leptin signal: leptin resistance. When cold-acclimated male field voles (Microtus Agrestis) are transferred from short (SD, 8 h light) to long (LD, 16 h light) photoperiods, they increase dramatically in body mass and fatness for about 4 weeks. After this period, their mass stabilizes at a new plateau about 25% higher than animals maintained in SD. The increase in adiposity is not caused by significant increases in food intake, but reflects an increase in digestive efficiency. Measures of circulating leptin reveal that the increased adiposity is matched by increased circulating leptin. By infusing voles with exogenous leptin, we have demonstrated that SD voles are leptin sensitive (reducing both body mass and food intake), whereas LD animals are leptin resistant. Voles may therefore be a useful model for understanding the process of leptin resistance. The change in leptin sensitivity in voles was not associated with changes in the levels of gene expression of the orexogenic or anorexogenic neuropeptides, such as neuropeptide Y, agouti-related peptide, POMC and cocaine- and amphetamine-regulated transcript, measured in the hypothalamic arcuate nucleus (ARC). During the phase that body mass was increasing, however, there was a transient increase in the ARC expression of suppressor of cytokine signalling-3 (SOCS3). These data suggest that the changes in the expression of SOCS3 in the ARC may be involved in leptin resistance. However, the mechanism by which these changes may be linked to alterations in digestive efficiency that underpin the changes in adiposity, or how the differences are signalled by changes in photoperiod, remains unclear.

  • photoperiod regulates leptin sensitivity in field voles Microtus Agrestis
    Journal of Comparative Physiology B-biochemical Systemic and Environmental Physiology, 2006
    Co-Authors: Ela Krol, J S Duncan, Paula Redman, Peter J Morgan, Julian G Mercer, John R Speakman
    Abstract:

    We have previously shown that cold-acclimated (8°C) male field voles (Microtus Agrestis) transferred from short (SD, 8:16 h L:D) to long photoperiod (LD, 16:8 h L:D) exhibit increases in body mass, adiposity and food intake. To assess whether these increases were associated with decreased leptin sensitivity, we infused LD and SD voles with physiological doses of murine leptin (or saline) delivered peripherally for 7 days via mini-osmotic pumps. Measurements were made of body mass (weight-reducing effect of leptin), food intake (anorectic effect of leptin) and gene expression of uncoupling protein 1 (UCP1) in brown adipose tissue (BAT) (thermogenic effect of leptin). The SD animals were sensitive to the weight-reducing effects of leptin (mean body mass decrease of 1.2 g over 7 days) and appetite-reducing effect of leptin (mean food intake decrease of 2.5 g over 7 days), whereas LD voles were resistant to the hormone treatment. The switch from a leptin-sensitive to leptin-resistant state appears to act as a desensitisation mechanism that allows voles transferred from SD to LD to ignore elevated leptin levels generated by increased body fat and accumulate adipose tissue without stimulating compensatory changes opposing the weight gain. Neither SD nor LD voles responded to infusion of leptin by changes in BAT UCP1 gene expression, suggesting dissociation of anorectic and thermogenic effects of leptin, possibly related to chronic cold exposure. Our results indicate that cold-acclimated voles show photoperiod-regulated changes in leptin sensitivity and may provide an attractive model for elucidating molecular mechanisms of leptin resistance.

  • effect of photoperiod on body mass food intake and body composition in the field vole Microtus Agrestis
    The Journal of Experimental Biology, 2005
    Co-Authors: Elzbieta Krol, Paula Redman, Julian G Mercer, John R Speakman, Clausdieter Mayer, P J Thomson, Rhiannan H Williams
    Abstract:

    Many small mammals respond to seasonal changes in photoperiod by altering body mass and adiposity. These animals may provide valuable models for understanding the regulation of energy balance. Here, we present data on the field vole (Microtus Agrestis) - a previously uncharacterised example of photoperiod-induced changes in body mass. We examined the effect of increased day length on body mass, food intake, apparent digestive efficiency, body composition, de novo lipogenesis and fatty acid composition of adipose tissue in cold-acclimated (8 degrees C) male field voles by transferring them from a short (SD, 8 h:16 h L:D) to long day photoperiod (LD, 16 h:8 h L:D). During the first 4 weeks of exposure to LD, voles underwent a substantial increase in body mass, after which the average difference between body masses of LD and SD voles stabilized at 7.5 g. This 24.8% increase in body mass reflected significant increases in absolute amounts of all body components, including dry fat mass, dry lean mass and body water mass. After correcting body composition and organ morphology data for the differences in body mass, only gonads (testes and seminal vesicles) were enlarged due to photoperiod treatment. To meet energetic demands of deposition and maintenance of extra tissue, voles adjusted their food intake to an increasing body mass and improved their apparent digestive efficiency. Consequently, although mass-corrected food intake did not differ between the photoperiod groups, the LD voles undergoing body mass increase assimilated on average 8.4 kJ day(-1) more than animals maintained in SD. The majority (73-77%) of the fat accumulated as adipose tissue had dietary origin. The rate of de novo lipogenesis and fatty acid composition of adipose tissue were not affected by photoperiod. The most important characteristics of the photoperiodic regulation of energy balance in the field vole are the clear delineation between phases where animals regulate body mass at two different levels and the rate at which animals are able to switch between different levels of energy homeostasis. Our data indicate that the field vole may provide an attractive novel animal model for investigation of the regulation of body mass and energy homeostasis at both organism and molecular levels.

  • the consequences of acute cold exposure on protein oxidation and proteasome activity in short tailed field voles Microtus Agrestis
    Free Radical Biology and Medicine, 2002
    Co-Authors: Colin Selman, John R Speakman, Jane S Mclaren, Tilman Grune, Alexandra Stolzing, Manuela Jakstadt
    Abstract:

    During cold exposure, animals upregulate their metabolism and food intake, potentially exposing them to elevated reactive oxygen species (ROS) production and oxidative damage. We investigated whether acute cold (7 ± 3°C) exposure (1, 10, or 100 h duration) affected protein oxidation and proteasome activity, when compared to warm controls (22 ± 3°C), in a small mammal model, the short-tailed field vole Microtus Agrestis. Protein carbonyls and the chymotrypsin-like proteasome activity were measured in plasma, heart, liver, kidney, small intestine (duodenum), skeletal muscle (gastrocnemius), and brown adipose tissue (BAT). Trypsin-like and peptidyl-glutamyl-like proteasome activities were determined in BAT, liver, and skeletal muscle. Resting metabolic rate increased significantly with duration of cold exposure. In skeletal muscle (SM) and liver, protein carbonyl levels also increased with duration of cold exposure, but this pattern was not repeated in BAT where protein carbonyls were not significantly elevated. Chymotrpsin-like proteasome activity did not differ significantly in any tissue. However, trypsin-like activity in SM and peptidyl-glutamyl-like activity in both skeletal muscle and liver, were reduced during the early phase of cold exposure (1–10 h), correlated with the increased carbonyl levels in these tissues. In contrast there was no reduction in proteasome activity in BAT during the early phase of cold exposure and peptidyl-glutamyl-like activity was significantly increased, correlated with the lack of accumulation of protein carbonyls in this tissue. The upregulation of proteasome activity in BAT may protect this tissue from accumulated oxidative damage to proteins. This protection may be a very important factor in sustaining uncoupled respiration, which underpins nonshivering thermogenesis at cold temperatures.

Maarit Jaarola - One of the best experts on this subject based on the ideXlab platform.

  • genetic variation in field voles Microtus Agrestis from the british isles selective sweeps or population bottlenecks
    Biological Journal of The Linnean Society, 2019
    Co-Authors: Jeremy S Herman, Maarit Jaarola, Joanna Stojak, Joana Pauperio, Jan M Wojcik, Jeremy B Searle
    Abstract:

    The Eurasian field vole (Microtus Agrestis) comprises three evolutionarily significant units (ESUs). The northern ESU is found at higher latitudes across the western Palaearctic region and includes six, largely allopatric, mitochondrial DNA lineages that were derived from population bottlenecks. One of these lineages is found in southern Britain and nearby areas of continental Europe. A prominent sub-lineage is nested within, and therefore derived from, the part of this lineage occupying southern Britain. The sub-lineage consists of an abundant central haplotype together with a series of closely related haplotypes, a distribution that would result from either a recent population bottleneck or a selective sweep. To distinguish between these, we sequenced a Y-chromosome marker in 167 field voles from Britain and Europe, and analysed a panel of 13 autosomal microsatellite loci in 144 field voles from eight populations in Britain. The Y-chromosome marker showed a continental-scale pattern of variation that was not aligned with that of the mitochondrial marker, while microsatellite variation did not show any evidence for a bottleneck, tentatively favouring selection instead. This implies a role for both stochastic and selective processes in generating phylogeographical patterns at different scales in the field vole.

  • Microtus Agrestis (Rodentia: Cricetidae)
    Mammalian Species, 2017
    Co-Authors: Maria Da Luz Mathias, E. Blake Hart, Maria Da Graça Ramalhinho, Maarit Jaarola
    Abstract:

    Microtus Agrestis (Linnaeus, 1761) is a relatively small microtine rodent commonly called the field vole. It has a compact body, blunt oval head, short round ears that barely protrude from the fur, and a short, bicolored, rather stiff tail. It is easily confused with sympatric or parapatric Microtus arvalis, M. oeconomus, and M. levis (M. rossiaermeridonalis) with indistinguishable juveniles. There is geographical variation of size and coloration ranging across Europe south from the Pyrenees to the Arctic coast and Alps eastward to the River Yenisei and Lake Baikal in Asia up to elevations of 2,100 m. It prefers wet meadow areas, riverside habitats, and forests with dense herbaceous cover. M. Agrestis is considered to represent a trace of a 1st radiation of the genus Microtus in Europe.

  • land bridge calibration of molecular clocks and the post glacial colonization of scandinavia by the eurasian field vole Microtus Agrestis
    PLOS ONE, 2014
    Co-Authors: Jeremy S Herman, Maarit Jaarola, Jan M Wojcik, Allan D Mcdevitt, Agata Kawalko, Jeremy B Searle
    Abstract:

    Phylogeography interprets molecular genetic variation in a spatial and temporal context. Molecular clocks are frequently used to calibrate phylogeographic analyses, however there is mounting evidence that molecular rates decay over the relevant timescales. It is therefore essential that an appropriate rate is determined, consistent with the temporal scale of the specific analysis. This can be achieved by using temporally spaced data such as ancient DNA or by relating the divergence of lineages directly to contemporaneous external events of known time. Here we calibrate a Eurasian field vole (Microtus Agrestis) mitochondrial genealogy from the well-established series of post-glacial geophysical changes that led to the formation of the Baltic Sea and the separation of the Scandinavian peninsula from the central European mainland. The field vole exhibits the common phylogeographic pattern of Scandinavian colonization from both the north and the south, however the southernmost of the two relevant lineages appears to have originated in situ on the Scandinavian peninsula, or possibly in the adjacent island of Zealand, around the close of the Younger Dryas. The mitochondrial substitution rate and the timescale for the genealogy are closely consistent with those obtained with a previous calibration, based on the separation of the British Isles from mainland Europe. However the result here is arguably more certain, given the level of confidence that can be placed in one of the central assumptions of the calibration, that field voles could not survive the last glaciation of the southern part of the Scandinavian peninsula. Furthermore, the similarity between the molecular clock rate estimated here and those obtained by sampling heterochronous (ancient) DNA (including that of a congeneric species) suggest that there is little disparity between the measured genetic divergence and the population divergence that is implicit in our land-bridge calibration.

  • asymmetric and differential gene introgression at a contact zone between two highly divergent lineages of field voles Microtus Agrestis
    Journal of Evolutionary Biology, 2012
    Co-Authors: Mathias Beysard, Maarit Jaarola, Gerald Heckel, Peter Vogel
    Abstract:

    Secondary contact zones have the potential to shed light on the mode and rate at which reproductive isolation accumulates during allopatric speciation. We investigated the population genetics of a contact zone between two highly divergent lineages of field voles (Microtus Agrestis) in the Swiss Jura mountains. To shed light on the processes underlying introgression, we used maternally, paternally, and bi-parentally inherited markers. Though the two lineages maintained a strong genetic structure, we found some hybrids and evidence of gene flow. The extent of introgression varied with the mode of inheritance, being highest for mtDNA and absent for the Y chromosome. In addition, introgression was asymmetric, occurring only from the Northern to the Southern lineage. Both patterns seem parsimoniously explained by neutral processes linked to differences in effective sizes and sex-biased dispersal rates. The lineage with lower effective population size was also the more introgressed, and the mode-of-inheritance effect correlated with the male-biased dispersal rate of microtine rodents. We cannot exclude, however, that Haldane’s effect contributed to the latter, as we found a marginally significant deficit in males (the heterogametic sex) among hybrids. We propose a possible demographic scenario to account for the patterns documented, and empirical extensions to further investigate this contact zone.

  • the behavior during pachynema of a normal and an inverted y chromosome in Microtus Agrestis
    Hereditas, 2008
    Co-Authors: Terry Ashley, Maarit Jaarola, Karl Fredga
    Abstract:

    The pachytene behavior of the chromosomes of Microtus Agrestis (L.) (Rodentia, Arvicolidae) males carrying either the standard, or the pericentrically inverted Lund Y chromosome have been examined by electron microscopy of microspread spermatocytes. There is no synapsis between the X and either the standard or the Lund Y chromosomes during any substage of pachynema. Since synapsis is generally considered a prerequisite for crossing over, there appears to be no opportunity for crossover or chiasma formation between the X and Y in this species. The G-, C- and NOR-banded mitotic karyotypes of animals carrying the standard and Lund Y are also presented.

Michael T. Rogan - One of the best experts on this subject based on the ideXlab platform.

  • identification of a new species of digenean notocotylus malhamensis n sp digenea notocotylidae from the bank vole myodes glareolus and the field vole Microtus Agrestis
    Parasitology, 2012
    Co-Authors: K Boyce, Philip D Harris, C Reynolds, Geoff Hide, Philip S Craig, Andrew Pickles, Michael T. Rogan
    Abstract:

    Notocotylus malhamensis n. sp. is described from the caecum of the bank vole (Myodes glareolus) and the field vole (Microtus Agrestis) from Malham Tarn Nature Reserve in North Yorkshire, UK. In total, 581 specimens were collected from rodents trapped at a wetland site (Tarn Fen) between July 2010 and October 2011 with a prevalence of 66·7% and mean intensity of 94·6 in the bank vole and 50% prevalence and a mean intensity of 4·3 in the field vole. This species appears to be most closely related to other previously described Notocotylus species infecting rodents in Europe but differs principally by the metraterm to cirrus sac ratio (1:1·5–1:1·2) in combination with a densely spinulated cirrus, simple caeca and a greater number of ventral glands in the lateral rows (14–17). The use of molecular differentiationwas of limited use in this study due to a paucity of relevant information in the DNA sequence databases. However, the complete ITS1-5.8S rDNA-ITS2 and partial 28S gene sequences have been generated to provide a definitive tool for identification of this species in future studies. As far as we know this is the first report of a notocotylid infection in M. glareolus in the UK.

  • identification of a new species of digenean notocotylus malhamensis n sp digenea notocotylidae from the bank vole myodes glareolus and the field vole Microtus Agrestis
    Parasitology, 2012
    Co-Authors: K Boyce, Philip D Harris, C Reynolds, Geoff Hide, Philip S Craig, Andrew Pickles, Michael T. Rogan
    Abstract:

    Notocotylus malhamensis n. sp. is described from the caecum of the bank vole (Myodes glareolus) and the field vole (Microtus Agrestis) from Malham Tarn Nature Reserve in North Yorkshire, UK. In total, 581 specimens were collected from rodents trapped at a wetland site (Tarn Fen) between July 2010 and October 2011 with a prevalence of 66·7% and mean intensity of 94·6 in the bank vole and 50% prevalence and a mean intensity of 4·3 in the field vole. This species appears to be most closely related to other previously described Notocotylus species infecting rodents in Europe but differs principally by the metraterm to cirrus sac ratio (1:1·5–1:1·2) in combination with a densely spinulated cirrus, simple caeca and a greater number of ventral glands in the lateral rows (14–17). The use of molecular differentiationwas of limited use in this study due to a paucity of relevant information in the DNA sequence databases. However, the complete ITS1-5.8S rDNA-ITS2 and partial 28S gene sequences have been generated to provide a definitive tool for identification of this species in future studies. As far as we know this is the first report of a notocotylid infection in M. glareolus in the UK.

K Boyce - One of the best experts on this subject based on the ideXlab platform.

  • identification of a new species of digenean notocotylus malhamensis n sp digenea notocotylidae from the bank vole myodes glareolus and the field vole Microtus Agrestis
    Parasitology, 2012
    Co-Authors: K Boyce, Philip D Harris, C Reynolds, Geoff Hide, Philip S Craig, Andrew Pickles, Michael T. Rogan
    Abstract:

    Notocotylus malhamensis n. sp. is described from the caecum of the bank vole (Myodes glareolus) and the field vole (Microtus Agrestis) from Malham Tarn Nature Reserve in North Yorkshire, UK. In total, 581 specimens were collected from rodents trapped at a wetland site (Tarn Fen) between July 2010 and October 2011 with a prevalence of 66·7% and mean intensity of 94·6 in the bank vole and 50% prevalence and a mean intensity of 4·3 in the field vole. This species appears to be most closely related to other previously described Notocotylus species infecting rodents in Europe but differs principally by the metraterm to cirrus sac ratio (1:1·5–1:1·2) in combination with a densely spinulated cirrus, simple caeca and a greater number of ventral glands in the lateral rows (14–17). The use of molecular differentiationwas of limited use in this study due to a paucity of relevant information in the DNA sequence databases. However, the complete ITS1-5.8S rDNA-ITS2 and partial 28S gene sequences have been generated to provide a definitive tool for identification of this species in future studies. As far as we know this is the first report of a notocotylid infection in M. glareolus in the UK.

  • identification of a new species of digenean notocotylus malhamensis n sp digenea notocotylidae from the bank vole myodes glareolus and the field vole Microtus Agrestis
    Parasitology, 2012
    Co-Authors: K Boyce, Philip D Harris, C Reynolds, Geoff Hide, Philip S Craig, Andrew Pickles, Michael T. Rogan
    Abstract:

    Notocotylus malhamensis n. sp. is described from the caecum of the bank vole (Myodes glareolus) and the field vole (Microtus Agrestis) from Malham Tarn Nature Reserve in North Yorkshire, UK. In total, 581 specimens were collected from rodents trapped at a wetland site (Tarn Fen) between July 2010 and October 2011 with a prevalence of 66·7% and mean intensity of 94·6 in the bank vole and 50% prevalence and a mean intensity of 4·3 in the field vole. This species appears to be most closely related to other previously described Notocotylus species infecting rodents in Europe but differs principally by the metraterm to cirrus sac ratio (1:1·5–1:1·2) in combination with a densely spinulated cirrus, simple caeca and a greater number of ventral glands in the lateral rows (14–17). The use of molecular differentiationwas of limited use in this study due to a paucity of relevant information in the DNA sequence databases. However, the complete ITS1-5.8S rDNA-ITS2 and partial 28S gene sequences have been generated to provide a definitive tool for identification of this species in future studies. As far as we know this is the first report of a notocotylid infection in M. glareolus in the UK.

Heikki Henttonen - One of the best experts on this subject based on the ideXlab platform.