Associations between energetics and over-winter survival in the short-tailed field vole Microtus agrestis. (original) (raw)
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Summer acclimatization in the short-tailed field vole, Microtus agrestis.
Journal of comparative Physiology B, 1996
We investigated the changes that occurred in basal and noradrenaline-induced metabolic rate, body temperature and body mass in short-tailed field voles, Microtus aqrestis, during exposure to naturally increas ing photoperiod and ambient temperature. These param eters were first measured in winter-acclimatized voles (n = 8) and then in the same xoles which had been allowed to seasonally acclimatize to photoperiod and ambient temperature (6 months later). Noradrenaline induced metabolic rate, basal metabolic rate and non shi vering thermogenesis were significantly higher in winter-acclimatized compared to summer-acclimatized voles. There was a significant positive relationship be tween 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 be tween body mass and noradrenaline-induced metabolic rate in both winter-acclimatized and summer-acclima tized 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 temper ature 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 dur ing cold exposure, since basal metabolic rate increased
Winter is energetically challenging for small herbivores because of greater energy requirements for thermogenesis at a time when little energy is available. We formulated a model predicting optimal wintering body size, accounting for the scaling of both energy expenditure and assimilation to body size, and the trade-off between survival benefits of a large size and avoiding survival costs of foraging. The model predicts that if the energy cost of maintaining a given body mass differs between environments, animals should be smaller in the more demanding environments, and there should be a negative correlation between body mass and daily energy expenditure (DEE) across environments. In contrast, if animals adjust their energy intake according to variation in survival costs of foraging, there should be a positive correlation between body mass and DEE. Decreasing temperature always increases equilibrium DEE, but optimal body mass * $15.00. All rights reserved. may either increase or decrease in colder climates depending on the exact effects of temperature on mass-specific survival and energy demands. Measuring DEE with doubly labeled water on wintering Microtus agrestis at four field sites, we found that DEE was highest at the sites where voles were smallest despite a positive correlation between DEE and body mass within sites. This suggests that variation in wintering body mass between sites was due to variation in food quality/availability and not adjustments in foraging activity to varying risks of predation.
2009
Arvicoline rodents (voles and lemmings) inhabit high-latitude environments and undergo pronounced seasonal changes in their physiology and behavior. They are an important prey resource in circumpolar regions, and their population numbers can affect the survival and reproductive fitness o f many predator and secondary prey species. I studied the effects of seasonality and environmental factors on reproduction and energy allocation in the northern red-backed vole (.Myodes rutilus), an arvicoline rodent in Alaska known to have bred in winter. My overall aim was to measure the effects of season and environmental factors on the reproductive axis, body composition, and energy expenditure of this animal. I validated a dual-energy X-ray absorptiometry (DXA) apparatus for use in determining fat and lean tissue, body water, protein, and mineral content in M. rutilus (R2 = 0.65 to 0.98, p < 0.001 for all parameters). Absolute fat, but not percentage fat changed seasonally. Reproductive organ masses reached peak levels in spring (females) and early summer (males), and significant co-variates were photoperiod, temperature, snow cover, body mass, and percent fat (depending on breeding period and gender). I found one instance o f late-summer male non-responsiveness, but no winter breeding. However, 28.2% o f captive, lab-raised male voles were non-responsive to short days {ad lib. food and water at 20°C), which was within the 20-40% frequency range known for lower latitude species. Differences were found at the gonadal level and pituitary level (testosterone and luteinizing hormone (LH) either varied by group and/or were correlated with testis mass), while differences at the hypothalamic level (gonadotropin-releasing hormone immunoreactivity (GnRH-ir) and gonadotropininhibiting hormone (GnlH)-ir cell counts) were inconclusive. Body composition and relative visceral organ mass changed seasonally, and significant covariates were photoperiod (mass, %protein, %mineral), gender (intestines), and temperature (heart). Field metabolic rate did not differ by breeding period, but was significantly correlated with temperature. Bone mineral density (BMD) of voles was highest in early summer and lowest in winter, whereas the BMD o f two hibernating mammals did not change during winter torpor. These findings could help to identify the mechanisms underpinning arvicoline rodent population cycling and to predict physiological and ecological responses of small mammals to different climate change scenarios. invaluable in my education and training. I would especially like to thank Dr. van Tets for funding this research from his grants and for the hours he invested into advising me and revising my manuscripts. Thank you to all of my professors, including Drs. Sasha Kitaysky and Jerry Kudenov. I would like to thank the post docs, graduate and undergraduate students, NIH-NIDDK high school students, and UAA/UAF staff that contributed to the success of this research. Special thanks are due to Fredha Olson, April Brennan, UAF Animal Quarters for the time they invested. I would also like to thank my lab mates and other graduate students that provided laughter and conversation over the years. On a personal note, I would like to thank my wife, Devon, who has supported me, served me, loved me, and endured with me throughout the years of graduate school with unwavering encouragement and limitless grace. Completion of my degrees could not have been possible without your help and patience. I am forever grateful. To my daughter, Moriah, you have been a never-ending source of love and happiness. Thank you for your smiles and hugs that I could count on every day when I returned home. To my parents, James and Janice, and other family members who helped to spur me on to completion, thank you for your encouragement, love, and the opportunities you gave me to succeed. To my church family and friends, thank you for your counsel, prayers, and friendship. You have been precious to me. Finally, to Jesus Christ, my gracious Lord and Savior, you have walked with me every step of the way through this process. I have infinite joy in You. Thank you for loving and dying for this wretched sinner. XV 1 Chapter 1: 'S tevenson K T, van T ets 1G. 2008. D ual-E nergy X-R ay A bsorptiom etry (D X A) can accurately and n o n destructively m easure the body condition o f sm all, free-living rodents. P hysioI B iochem Z ool 81 (3):3 7 1-382.
journal of comparative physiology, 2019
Rodents colonising subterranean environments have developed several morphological, physiological and behaviour traits that promote the success of individuals in such demanding conditions. Resting metabolic rate, thermoregulation capacity and daily energy expenditure were analysed in two semi-fossorial pine-vole species Microtus lusitanicus and Microtus duodecimcostatus inhabiting distinct areas of the Iberian Peninsula. Individuals capture location varied in habitat and soil features, allowing the comparison of energetic parameters with ecological characteristics, that can help explain the use of the subterranean environment and dependence of the burrow system. Results showed that M. duodecimcostatus has lower mass independent resting metabolic rate when compared with M. lusitanicus, which may be a response to environmental features of their habitat, such as dryer soils and lower water availability. Thermal conductance increased with body mass and was dependent on the ambient temperature. No significant differences were observed in the daily energy expenditure, but water economy data demonstrated the influence of the water available in the habitat on the energetics of voles. These species may rely on behavioural adaptations and seasonal use of burrows to cope with thermal challenges of subterranean activity and soil constraints. We found strong evidence that M. lusitanicus is able to use torpor as a response to low ambient temperatures which is a new observation among Arvicolines.
Metabolism and thermoregulation in the Levant vole Microtus guentheri: The role of photoperiodicity
Journal of Thermal Biology, 1994
l. The populations of the Levant vole, Micro&s guentheri, inhabiting the Mediterranean ecosystem of Israel, are marginal populations which seem to be well adapted to its long dry and warm season. The thermoregulatory and metabolic responses of the Levant voles of Israel to manipulation of photoperiod were studied to assess the role of photoperiodicity in seasonal acclimatization.
Metabolism and thermoregulation in the Cabrera vole (Rodentia: Microtus cabrerae)
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2003
Metabolism and thermoregulation were studied for the first time in the Cabrera vole (Microtus cabrerae), an endemic and threatened rodent of the Iberian Peninsula. Low values of resting metabolic rate (RMR) were registered (1.13 mlO g h ) at the lower limit of the thermoneutral zone (TNZ) (around 33.5 8C). Body temperature increased near y1 y1 2 the TNZ up to 37.3 8C but remained stable, around 36 8C, at ambient temperatures below 25 8C. Values of thermal conductance remained quite stable at ambient temperatures of 10-25 8C (0.144-0.160 mlO g h 8C) and increased y1 y1 2 to 0.301 mlO g h 8C at 33.5 8C. Data revealed that M. cabrerae developed a highly adaptive ability of conserving y1 y1 2 energy and lowering the metabolic cost of thermoregulation at high ambient temperatures, allowing the body temperature to approximate that of the environment and exhibiting low resting metabolic rate and high conductance. ᮊ