Browsing by Author "Nespolo, RF"

Now showing 1 - 12 of 12
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    Arousal from torpor in the chilean mouse-opposum (Thylamys elegans)
    (1999) Opazo, JC; Nespolo, RF; Bozinovic, F
    We examined the effect of norepinephrine injections on non-shivering thermogenesis (NST), rewarming rate, and metabolic cost during torpor arousal in warm- and cool-acclimated Chilean mouse-opposums, Thylamys elegans. Warm- and cool-acclimated animals did not display NST in response to NE injections. Values of VO2 (resting, after saline and NE injections) were not significantly different within treatments. Rewarming rates of warm-acclimated animals did not differ significantly from those in cool-acclimated animals. In contrast, the metabolic cost of torpor arousal was significantly affected by acclimation temperature. Warm-acclimated animals required more energy for arousal than cool-acclimated animals. Our study suggests that the main thermoregulatory mechanism during torpor arousal in this Chilean marsupial is shivering thermogenesis, and that its amount can be changed by thermal acclimation. (C) 1999 Elsevier Science B.V. All rights reserved.
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    Effect of ambient temperature and energy demands on digestive functions in leaf-eared mice (Phyllotis darwini) from central Chile
    (1997) Bozinovic, F; Nespolo, RF
    The leaf-eared mouse, Phyllotis darwini, is a nocturnal rodent inhabiting the semiarid and Mediterranean habitats of northern and central Chile. Previous observations suggested that in the field, individuals may change food intake according to seasonal changes in ambient temperature. We therefore anticipated that P. darwini should increase food intake in response to lower ambient temperature. As predicted, results of food trials and digestive measurements demonstrated that P. darwini increases food intake and assimilation at lower ambient temperatures but does not increase food mean retention time. At lower ambient temperatures, individuals increase digestive tract size thus improving body mass maintenance and perhaps survival during winter.
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    Heritability of energetics in a wild mammal, the leaf-eared mouse (Phyllotis darwini)
    (2003) Nespolo, RF; Bacigalupe, LD; Bozinovic, F
    As a first examination of the additive genetic variance of thermoregulatory traits in a natural population of endotherms. we studied the quantitative genetics of key physiological ecology traits in the leaf-cared mouse, Phyllotis darwini. We measured basal metabolic rate (BMR), nonshivering thermogenesis (NST), maximum metabolic rate for thermoregulation (MMR), thermal conductance (C-T), body temperature (T-b), and factorial aerobic scope (FAS) in individuals acclimated to cold and warm conditions. For comparability with previous studies, we included the following morphological traits: foot length (F-L), total length (T-L), body mass (m(b), at birth, sexual maturity, 6 months, and 8 months). Variance components were obtained from two different procedures: the expected variance component in an ANOVA Type III sum of squares and an animal model approach using restricted maximum likelihood. Results suggest the presence of additive genetic variance in F-L (h(2) = 0.47, P = 0.045), C-T of cold-acclimated animals (h(2) = 0.66, P = 0.041). and night body temperature, measured in cold-acclimated animals (h(2) = 0.68, P = 0.080). Heritabilities of rub were near zero at all ages, but maternal effects and common environment effects were high and significant. We found no evidence of additive genetic variance in BMR, NST, MMR, or FAS (i.e., estimates were not significantly different from zero for all tests). Our results are in general agreement with previous studies of mammals that reported low heritability for: (1) BMR and MMR; (2) daytime body temperature; and (3) body mass for wild, but not laboratory or domestic, populations.
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    Heritability of progeny size in a terrestrial isopod: transgenerational environmental effects on a life history trait
    (2004) Carter, MJ; Lardies, MA; Nespolo, RF; Bozinovic, F
    Maternal effects, the environment that mothers provide to their offspring, their provision of nutrients and the environment that offspring of the same clutch share, have come to be recognized as an important influence on offspring fitness. In addition, in invertebrates, maternal effects and common environment may change according to a mother's diet. We tested for the changes in quantitative genetic parameters in a half-sib design where mothers were fed diets varying in nutrient content. Surprisingly, we found that not only maternal and common environmental variance changed with experimental diets but also there were significant changes in narrow-sense heritabilities, with corresponding h(2) values of 0.61 (high protein), 0.08 (high carbohydrate) and 0.001 ( equal carbohydrate: protein). Our results show how an environmentally driven evolutionary process could occur in nature, since the response to selection could change dramatically according to the composition of the diet that females are ingesting.
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    Interplay among energy metabolism, organ mass and digestive enzyme activity in the mouse-opossum Thylamys elegans
    (2002) Nespolo, RF; Bacigalupe, LD; Sabat, P; Bozinovic, F
    The potential for thermal acclimation in marsupials is controversial. Initial studies suggest that the thermoregulatory maximum metabolic rate (MMR) in metatherians; cannot be changed by thermal acclimation. Nevertheless, recent studies reported conspicuous seasonality in both MMR and in basal metabolic rate (BMR). We studied the role of thermal acclimation in the Chilean mouse-opossum, Thylamys elegans, by measuring MMR and BMR before and after acclimation to cold or warm conditions. Following acclimation we also measured the mass of metabolically active organs, and the activity of a key digestive enzyme, aminopeptidase-N. No significant effect of thermal acclimation (i.e. between cold- and warm-acclimated animals) was observed for body mass, MMR, body temperature or factorial aerobic scope. However, the BMR of cold-acclimated animals was 30% higher than for warm-acclimated individuals. For organ mass, acclimation had a significant effect on the dry mass of caecum, liver and kidneys only. Stepwise multiple regression using pooled data showed that 71% of the variation in BMR is explained by the digestive organs. Overall, these results suggest that MMR is a rather rigid variable, while BMR shows plasticity. It seems that T. elegans cannot respond to thermal acclimation by adjusting its processes of energy expenditure (i.e. thermogenic capacity and mass of metabolically active organs). The lack of any significant difference in aminopeptidase-N specific activity between warm- and cold-acclimated animals suggests that this response is mainly quantitative (i.e. cell proliferation) rather than qualitative (i.e. differential enzyme expression). Finally, as far as we know, this study is the first to report the effects of thermal acclimation on energy metabolism, organ mass and digestive enzyme activity in a marsupial.
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    Intrapopulational variation in the standard metabolic rate of insects
    (2003) Nespolo, RF; Lardies, MA; Bozinovic, F
    Studies focusing on physiological variation among individuals, and its possible evolutionary consequences, are scarce. A trait can only be a target of natural selection if it is consistent over time, that is, a trait must be repeatable. In ectotherms it has been suggested that standard metabolic rate (MR) is related to Darwinian fitness, since it reflects energy usage and expenditure. The metabolic rate of the cricket Hophlosphyrum griseus was determined at three ambient temperatures. Repeatability of MR was estimated by product-moment correlation on residuals of body mass, as well as the thermal sensitivity of MR on an individual basis (individual Q(10)). The MR of H. griseus was significantly repeatable (r=0.53) and highly dependent on ambient temperature, and its sensitivity (Q(10)) was dependent on the temperature range. Our estimation of MR repeatability was high in comparison to published studies in vertebrates. Ours is the second report of repeatability (i.e. consistency over time of an individual's performance ranking within a population) of any aspect of energy metabolism in an insect, and also the first study to report significant repeatability of MR. Individual Q(10) values revealed important interindividual variation, which reflects the existence of intrapopulational variability in the thermal sensitivity of MR. In addition, individual Q(10) values were negatively correlated between temperature ranges. This means that crickets having low Q(10) at low temperatures, presented high Q(10) at high temperatures, and vice versa. Our results suggest that MR could be of selective value in insects, showing consistency over time and intrapopulational variability in its thermal dependence. Nevertheless, its heritability remains to be determined.
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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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    Quantitative genetics of bioenergetics and growth-related traits in the wild mammal, Phyllotis darwini
    (2005) Nespolo, RF; Bustamante, DM; Bacigalupe, LD; Bozinovic, F
    We studied the potential for response to selection in typical physiological-thermoregulatory traits of mammals such as maximum metabolic rate (MMR), nonshivering thermogenesis (NST) and basal metabolic rate (BMR) on cold-acclimated animals. We used an animal model approach to estimate both narrow-sense heritabilities (h(2)) and genetic correlations between physiological and growth-related traits. Univariate analyses showed that MMR presented high, significant heritability (h(2) = 0.69 - 0.35, asymptotic standard error), suggesting the potential for microevolution in this variable. However, NST and BMR presented low, nonsignificant h2, and NST showed large maternal/common environmental/nonadditive effects (c(2) = 0.34 +/- 0.17). Heritabilities were large and significant (h(2) > 0.5) for all growth-related traits (birth mass, growth rate, weaning mass). The only significant genetic correlations we found between a physiological trait and a growth-related trait was between NST and birth mass (r = -0.74; P < 0.05). Overall, these results suggest that additive genetic variance is present in several bioenergetic traits, and that genetic correlations could be present between those different kinds of traits.
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    The influence of heat increment of feeding on basal metabolic rate in Phyllotis darwini (Muridae)
    (2003) Nespolo, RF; Bacigalupe, LD; Bozinovic, F
    One of the most important prerequisites for obtaining a reliable measure of basal metabolic rate (BMR) in endotherms is that the animal must be in a post-absorptive condition. However, because of the diversity of nutrition and digestion modes in vertebrates, it is not simple to generalize a standard procedure for BMR measurement. Thus, information in this regard must be experimentally obtained by measuring the heat increment of feeding (HIF). We used a repeated-measures design to test for the effects of HIF on BMR in Phyllotis darwini, a granivorous rodent. Our results suggest that, in this species, feeding induces an elevation in O-2 consumption that can persist up to 4 h after the last meal. In addition, and irrespective of the fasting period, measures made with less than 2 h of fasting yield BMR values that are significantly higher than measurements after longer fasting periods (i.e. 3 and 4 h). (C) 2002 Elsevier Science Inc. All rights reserved.
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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.
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    Water economy of three Cinclodes (Furnariidae) species inhabiting marine and freshwater ecosystems
    (2004) Sabat, P; Nespolo, RF; Bozinovic, F
    Birds living in desert environments have been the preferred models for the study of physiological adaptations to water scarcity. Passerine birds living in marine coastal habitats face similar problems, yet physiological adaptations to water conservation in such species have been poorly documented. We measured total evaporative water loss (TEWL) and rates of oxygen consumption (VO2) in three species of passerine birds dwelling in marine and fresh water habitats. Mass specific total evaporative water loss was significantly lower in the marine species, Cinclodes nigrofumosus, than in species inhabiting areas near freshwater sources. We found a positive relationship between TEWL and VO2. The ratio of TEWL to VO2 (relative evaporative water loss, RTEWL) showed significant variation among Cinclodes species, and was highest for the fresh-water living species, C. oustaleti and C. fuscus. The variation in TEWL found in Cinclodes is likely a consequence of differential exploitation of marine prey with high osmotic loads, which, in turn, may impose the need for water conservation.
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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.