Browsing by Author "Rezende, EL"

Now showing 1 - 6 of 6
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    Activity and space use by degus: A trade-off between thermal conditions and food availability?
    (2003) Bacigalupe, LD; Rezende, EL; Kenagy, GJ; Bozinovic, F
    We analyzed the influence of environmental temperature (open versus shaded habitat) and experimental food availability on surface activity of the degu (Octodon degus), a day-active herbivorous rodent that inhabits central Chile. We manipulated food availability and compared open and shaded study plots to determine the influence of thermal conditions on aboveground activity. Degus displayed a bimodal pattern of daily activity during relatively warmer thermal conditions in the austral autumn, whereas activity was unimodal during colder conditions in winter. However, they had a unimodal activity pattern under warm conditions in the shade when food availability was artificially enhanced in autumn. We observed more animals active in the plots where food was supplemented under all conditions. Our results illustrate spatial and temporal shifts in activity of degus involving a trade-off based on avoidance of exposure to heat and the search for food.
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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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    Passerines versus nonpasserines
    (2002) Rezende, EL; Swanson, DL; Novoa, FF; Bozinovic, F
    We analyzed and compared the scaling of both basal and maximal thermogenic metabolic rates in passerine and nonpasserine birds using conventional and phylogenetic methods. In spite of the presumed adaptive importance of both metabolic traits, few studies concerning both their relationships and their ecological and evolutionary constraints have been conducted. We found no statistical differences in the scaling of maximal metabolic rate between passerines and nonpasserines; hence, we suggest the use of a single allometric regression for this trait in birds. In addition, basal and maximal metabolic rates were indeed correlated after removing the effects of body mass and phylogeny. The apparent generality of this correlation within both birds and mammals reinforces the need for general ecological and physiological explanations for the evolution of endothermy.
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    Patterns of daily activity in the leaf-eared mouse (Phyllotis darwini)
    (2001) Rezende, EL; Bozinovic, F
    The daily locomotor activity pattern of the nocturnal sigmodontine rodent Phyllotis darwini was analysed when faced with a differential offer of food. Animals with restricted food supply were less active during the day compared to animals who had access to food ad libitum, but no differences in activity were observed during the night. Minimization of energy expenditure may account for this behavioural plasticity, and such flexibility is extremely important in the unpredictable and low productive environments inhabited by P. darwini. (C) 2001 Academic Press.
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    Standard and comparative energetics of a small avian herbivore (Phytotoma rara)
    (2001) Rezende, EL; López-Calleja, MV; Bozinovic, F
    We studied the standard and comparative energetics of the Rufous-tailed Plancutter (Phytotoma rara), one of the smallest avian herbivores. The Rufous-tailed Plancutter had basal metabolic rate (BMR) values that so far are the highest mass-independent values observed in avian herbivores. Probably the BMR values attained by P.rara reflect its geographic distribution in temperate environments. Using a comparative analysis,we observed that herbivorous birds from temperate geographic areas tend to have higher BMR than tropical ones.
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    When nonshivering thermogenesis equals maximum metabolic rate
    (2001) Nespolo, RF; Bacigalupe, LD; Rezende, EL; Bozinovic, F
    Many small mammals inhabiting fluctuating and cold environments display enhanced capacity for seasonal changes in nonshivering thermogenesis (NST) and thermoregulatory maximum metabolic rate (MMR). However, it is not known how this plasticity remains in a mammal that rarely experiences extreme thermal fluctuations. In order to answer this question, we determined body mass (m(b)), basal metabolic rate (BMR), NST, MMR, and minimum thermal conductance (C) on a Chilean fossorial caviomorph (Spalacopus cyanus) from a coastal population, acclimated to cold (15 degreesC) and warm (30 degreesC) conditions. NST was measured as the maximum response of metabolic rate (NSTmax) after injection of norepinephrine (NE) in thermoneutrality minus BMR. Maximum metabolic rate was assessed in animals exposed to enhanced heat-loss atmosphere (He-O-2) connected with an open-flow respirometer. Body mass and metabolic variables increased significantly after cold acclimation with respect to warm acclimation but to a low extent (BMR, 26%; NST, 10%; and MMR, 12%). However, aerobic scope (MMR/BMR), calculated shivering thermogenesis (ST), and C did not change with acclimation regime. Our data suggest that physiological plasticity of S. cyanus is relatively low, which is in accordance with a fossorial mode of life. Although little is known about MMR and NST in fossorial mammals, S. cyanus has remarkably high NST; low MMR; and surprisingly, a nil capacity of ST when compared with other rodents.