Browsing by Author "Rosenmann, M"

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    Does thermal history affect metabolic plasticity?
    (2001) Rezende, EL; Silva-Durán, I; Novoa, FF; Rosenmann, M
    (1) The aim of this study was to understand the effects of thermal history in metabolic features such as maximum (MMR) and basal (BMR) metabolic rates, as well as in metabolic plasticity, considered as the total variation of MMR and BMR during the acclimation period, (2) We studied three species of the genus Phyllotis, from different thermal environments, in an altitudinal gradient from sea level to 3800 m.a.s.l. Animals were acclimated to contrasting temperatures of 5 and 30 degreesC. To determine the metabolic flexibility, MMR was measured at intervals of 6 days during the acclimation period, while BMR values were obtained at the end of acclimations. Aerobic scope and the rates of change of MMR were estimated in all populations. (3) High- and low-altitude rodents did not show differences in BMR. However, both upper and lower limits of MMR, as well as aerobic scope, were significantly different between high- and low-altitude species, indicating similar ranges of metabolic plasticity. On the other hand, the rates of change of MMR were similar in all populations. (4) Our results indicate that thermal history has a profound effect on the individuals' thermogenic capacity, probably in both phylogenetic and ontogenetic levels. Low-altitude species could not increase MMR to the same levels as high-altitude species, while the later were unable to decrease MMR to achieve the values of the low-altitude species. (C) 2001 Elsevier Science Ltd. All rights reserved.
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    Energetics and torpor of a South American "living fossil", the microbiotheriid Dromiciops gliroides
    (2004) Bozinovic, F; Ruiz, G; Rosenmann, M
    We examined the energetics of the living fossil microbiotheriid Dromiciops gliroides, a nocturnal and rare small marsupial, endemic to the northern portion of the temperate forest of southern South America. We investigated the effects of changes at ambient temperature and food restriction on the energetics and patterns of torpor. We determined whether they exhibit shallow daily torpor or deep prolonged torpor like some Australian marsupials. Thermal conductance was 92.5% of the expected value for a similarly sized eutherian and basal metabolic rate was 82.9 and 58.6% of the predicted value for standard metatherians and eutherians, respectively. Euthermic D. gliroides showed daily fluctuations in body temperature, being significantly higher during the night. Dromiciops gliroides entered torpor and aroused spontaneously. The duration of torpor bouts increased in response to decreasing ambient temperature; torpor bout duration ranged from 10 h at 20degreesC to 120 h at 12.5degreesC. This study is the first record of deep torpor or hibernation for a South American mammal. Torpor in this species as well as in marsupials in general appears to be an opportunistic response to unpredictable biotic and abiotic conditions.
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    Energetics thermoreoulation and torpor in the Chilean mouse-opossum Thylamys elegans (Didelphidae)
    (2005) Bozinovic, F; Ruiz, G; Cortés, A; Rosenmann, M
    In this paper we Studied the energetics and thermoregulation of the Chilean mouse-opossum Thylamys elegans (Dielphidae) a nocturnal small marsupial, endemic Of Southern South America. We Studied their standard energetic and determined whether they exhibit shallow daily torpor or deep prolonged torpor as a function of ambient temperature and food availability. Thylamys elegans partially supports the hypothesis that Neotropical marsupials have somewhat a higher basal metabolic rate (BMR) and thermal conductance (C-m) than Australian Ones. In fact, BMR was higher but C-m was lower than expected for their body mass, The higher mass-independent BMR of the Chilean mouse-opossum may be explained by its insectivorous food habits and its low C-m by its temperate habitats. Euthermic Chilean mouse-opossum showed daily fluctuations in body temperature being significantly hi-her during night time. In addition T. elegans entered in daily torpor and aroused spontaneously only was food was absent. That is, this species display a facultative type of daily torpor because propensity to enter in torpor was dependent of the combination of food absence and low ambient temperature. No torpor was observed when food was available. During torpor ambient temperature was slightly above ambient temperature between 0.3 to 0.5 degrees C. Torpor in this species as well as in marsupials in general. appears to be a flexible and an opportunistic response to unpredictable environmental conditions.
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    Intraspecific allometry of haematological parameters in Basilichthys australis
    (2002) Nespolo, RF; Rosenmann, M
    Allometry of haematological parameters (haematocrit, erythrocyte number, mean cell volume and haemoglobin concentration) of Basilichthys australis, suggested that small individuals and juveniles had larger red blood cells, less haemoglobin per volume of blood, and more diluted plasma than large and mature animals. (C) 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved.
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    Intraspecific differences in metabolic rate of Chroeomys olivaceus (Rodentia: Muridae)
    (2005) Novoa, FF; Rivera-Hutinel, A; Rosenmann, M; Sabat, P
    Studies of metabolic capacities in rodents have been largely Studied at an inter-specific levels, but physiological capacities of populations belonging to the same species have received lesser attention. Here we studied the maximum and basal metabolic rates Of two Populations of the rodent Chroeomys olivaceus dwelling in habitats with contrasting temperature and rainfall regimes, and to test if differences ill metabolic capacities are due to local adaptation or acclimatization effect. After four weeks of acclimation to 25 and 10 degrees C, the BMR arid MMR were determined in individuals from the northern population of Caleta Loa, and the southern population of La Picada. Individuals front 'La Picada' Population were heavier than those from Caleta Loa. MMR and BMR exhibited higher values in cold acclimated animals compared with warm-acclimated animals. Besides, BMR, but not MMR, was lower in Caleta Loa individuals, in spite of the acclimation treatment. Hence, the differences in the metabolic capacities and the response to acclimation of C. olivaceus populations appear to be an evolutionary response to the environmental cues.
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    Modulating factors of the energetic effectiveness of huddling in small mammals
    (1998) Canals, M; Rosenmann, M; Novoa, FF; Bozinovic, F
    Huddling is effective in decreasing metabolic rate permitting energy saving. However, this decrease varies among different species depending on physical, physiological and behavioral characteristics of the huddled individuals. Following a general model we analyzed the effects of ambient temperature, thermal conductance and ontogeny on the huddling effectiveness (energy saving level from huddling behaviour) in white mice Mas musculus. Also, we studied the effects of thermal conductance by using the Sigmodontine Abrothrix andinus as a model organism. To put our results in a general context we analyzed literature data of huddling of several species of rodents at different temperatures. No effects of temperature and thermal conductance was detected. However, based on literature data, we found that at temperatures lower or near thermoneutrality the huddling effectiveness decrease. Also, the huddling effectiveness depends on the stage of development. Temperature probably affects the intensity of huddling, while changes in huddling effectiveness at early stages of development are likely consequences of structural (morphological) changes during the ontogeny. In this sense, it appears that the capacity to change the body form is and individual structural constraint which is extended to the huddling group.
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    Thermal acclimation, maximum metabolic rate, and nonshivering thermogenesis of Phyllotis xanthopygus (rodentia) in the Andes mountains
    (1999) Nespolo, RF; Opazo, JC; Rosenmann, M; Bozinovic, F
    We determined non-shivering thermogensis (NST) and maximum metabolic rate (MMR) as functions of thermal acclimation in a small mammal species in a seasonal environment. We studied the rodent Phyllotis xanthopygus (Muridae) living in the cool to cold climate of the high Andean Plateau of northern Chile. As expected, NST and MMR were constantly higher in cool-acclimated individuals. Nevertheless, the observed differences in shivering thermogenesis (ST) as a result of temperature acclimation (>200%) exceeded our expectations. The large contributions of ST was due to a 94% increase in MMR while a 49% of increased in NST Thus, changes in ST in P. xanthopygus account for most of the metabolic plasticity and thermogenic capability that enables this species to cope with thermal variations in the Andean environment.