Browsing by Author "Bacigalupe, LD"

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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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    Cost of living in free-ranging degus (Octodon degus)
    (2004) Bozinovic, F; Bacigalupe, LD; Vásquez, RA; Visser, GH; Veloso, C; Kenagy, GJ
    Animals process and allocate energy at different seasons at variable rates, depending on their breeding season and changes in environmental conditions and resulting physiological demands. Overall total energy expenditure, in turn, should either increase in some seasons due to special added demands (e.g. reproduction) or it could simply remain at about the same level, in which case the animals must show compensatory rebalancing of other expenditures that can be reduced. To test for the alternative hypotheses of seasonal variability or compensation, we measured total daily energy expenditure (DEE) in free-living degus (Octodon degus) at four seasons and followed this with determinations of basal metabolic rate (BMR) in the laboratory in the same individuals. DEE varied seasonally but was only significantly different (lower) in summer (non-breeding season), with a DEE:BMR ratio of only 1.6, whereas autumn, winter and spring DEE values were statistically indistinguishable from one another and showed DEE:BMR ratios ranging from 1.9 to 2.2. Our values of DEE in the field fall within the broad range of allometric expectation for herbivorous mammals in general, but the ratios of DEE:BMR are lower than expected. This, together with the lack of strong major shifts in total levels of DEE, suggests that degus are showing compensatory shifts among various categories of energy expenditure that allow them to manage their overall energy balance by minimizing total expenditure. (C) 2003 Elsevier Inc. All rights reserved.
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    Dynamic digestive responses to increased energy demands in the leaf-eared mouse (Phyllotis darwini)
    (2005) Naya, DE; Bacigalupe, LD; Bustamante, DM; Bozinovic, F
    A major area of interest in comparative physiology has been to understand how animals cope with changing environmental demands in time and space. The digestive system has been identified as one of the more sensitive systems to changes in environmental conditions. However, most research on this topic has evaluated these effects during peak energetic demands, which do not allow for evaluation of the dynamics of the digestive response along a more natural continuous gradient of environmental conditions. We examined phenotypic flexibility in digestive responses of the leaf-eared mouse Phyllotis darwini to increments in total energy demands ( via sequential exposure to 26, 12 and 0 degreesC). Additionally, we evaluated the effect of a moderate energy demand ( 12 degreesC) over three different time periods ( 7, 17 and 27 days) on digestive traits. Moderate increases in energy demand were associated with changes in the distribution of digesta in the gut, whereas higher increases in energy demand involved increases in the tissue mass of digestive organs. Time-course analysis showed that at 12 degreesC practically all digestive variables reached stable values within 7 days, which is in agreement with empirical data and theoretical deductions from cellular turnover rates. We conclude that although the input of energy and nutrients into the digestive tract is typically periodic, many aspects of digestive physiology are likely to be flexible in response to environmental variability over both short-term ( daily) and long-term ( seasonal) time scales.
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    Functional morphology and geographic variation in the digging apparatus of cururos (Octodontidae: Spalacopus cyanus)
    (2002) Bacigalupe, LD; Iriarte-Díaz, J; Bozinovic, F
    We studied morphological and functional variations in jaws of coastal and mountain populations of subterranean Spalacopus cyanus inhabiting soils with contrasting hardness. We found almost no morphological differentiation between populations in the variables we measured. However, there were clear differences in incisor resistance between them. Apparently, soil hardness did not represent a selective pressure on cururos' digging apparatus. An Andean origin of this genus could explain our results.
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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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    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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    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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    Testing the metabolic cold adaptation hypothesis: an intraspecific latitudinal comparison in the common woodlouse
    (2004) Lardies, MA; Bacigalupe, LD; Bozinovic, F
    The metabolic cold adaptation (MCA) hypothesis predicts an increase in the metabolic rate of ectotherms from cold environments compared with their more temperate counterparts. This adaptive hypothesis is one of the most controversial in physiological ecology, for which the evidence comes principally from the meta-analysis of data sets of arthropods. Important for the study of metabolic cold adaptation are comparisons at a geographic level, especially on a latitudinal scale, because mean annual temperature decreases towards high latitudes. Furthermore, few studies have conducted intraspecific comparisons of metabolic rates along a latitudinal gradient. We tested the MCA hypothesis in the common woodlouse, Porcellio laevis, using different populations along a distributional range with a wide range of mean ambient temperatures (5degrees, 12degrees, 18degrees and 25degreesC) in Chile. Our results demonstrated that metabolic rate increased towards low latitudes - that is, woodlice from the warmer (i.e. northern) part of the distribution range had markedly higher metabolic rates than those from the cooler (i.e. southern) region, for almost all experimental temperatures. Thus, our results provide direct evidence of intraspecific latitudinal differences in metabolism, rejecting the MCA hypothesis, which is more difficult to resolve with interspecific level comparisons.
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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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    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.