Browsing by Author "Bozinovic, F"

Now showing 1 - 20 of 58
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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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    Adaptive latitudinal shifts in the thermal physiology of a terrestrial isopod
    (2004) Castañeda, LE; Lardies, MA; Bozinovic, F
    Temperature is the most important abiotic factor affecting physiology, ecology and evolution in ectotherms. Do organisms broadly distributed along a latitudinal gradient adapt to local differences in temperature? In ectotherms this question has played a central role in evolutionary physiology. By means of an extensive field study and laboratory experiments, we tested the existence of local adaptations in thermal traits along 10degrees of latitude in northern-central Chile. We studied behavioural and thermal traits that have been directly connected with the thermal physiology of ectotherms, along the latitudinal gradient. Using three populations of the common woodlouse (terrestrial isopod), Porcellio laevis, we examined changes in thermal physiology traits (i.e. thermal tolerance, thermal performance) and behavioural traits (i.e. thermoregulation in the field and the laboratory). Performance (i.e. righting response speed) reached a maximum value at intermediate temperatures, and was highest for the northern population. Chill-coma temperature showed an increase towards high latitude, while heat-coma temperature did not vary between populations. On the other hand, optimum temperature was negatively correlated with latitude. Thus, southern woodlice appear to have evolved towards becoming low-temperature specialists, whereas woodlice from warm regions demonstrate low cold tolerance as well as a higher optimum temperature. Our results demonstrate that P. laevis woodlice from different parts of the distribution range show patterns in thermal physiology that covary with the thermal environment (i.e. latitude); thus, P laevis adapts to local environments to increase its performance.
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    An "enactive" approach to integrative and comparative biology: Thoughts on the table
    (2003) Palacios, AG; Bozinovic, F
    We discuss the concept of Enaction as originally proposed by Varela. We attempt to exemplify through two specific topics, sensory ecology and behavior, as well as physiological and behavioral ecology, on which the enactive approach is based. We argue that sensory physiology allows us to explore the biological and cognitive meaning of animal 'private' sensory channels, beyond the scope of our own sensory capacity. Furthermore, after analyzing the interplay between factors that may impose limits upon an animal's use of time and energy, we call for a program of research in integrative and comparative biology that simultaneously considers evolutionary ecology (including physiological and behavioral ecology) and neurobiology (including cognitive mechanisms as well structural design). We believe that this approach represents a shift in scientific attitude among biologists concerning the place of biological and ecological topics in studies of integrative and comparative biology and biological diversity and vice versa.
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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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    Behavioral and physiological thermoregulation of Atacama desert-dwelling Liolaemus lizards
    (2001) Labra, A; Soto-Gamboa, M; Bozinovic, F
    The behavioral and physiological thermoregulation of three Atacama desert-dwelling Liolaemus lizards was studied and compared with previous data on Liolaemus from other ecosystems. The thermoregulatory mechanisms of the desert-dwelling species differed from those of the others, a consequence of differences in the habitat structure of the species. Desert species have higher critical thermal minima and, contrary to expectations, lower selected body temperatures than Liolaemus from Mediterranean environments. Results of the rate,, of thermal time constants suggest mechanisms to cope with the fast decrease of environmental temperature that occurs in the desert during the mid-afternoons. Finally, the manner in which selection of low body temperatures may allow survival in desert conditions is discussed. Keywords: thermal time constants, operative temperature, physiological and behavioral thermoregulation.
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    Behavioral thermoregulation in the intertidal fish Girella laevifrons (Kyphosidae)
    (1999) Pulgar, J; Bozinovic, F; Ojeda, FP
    One of the key factors that determine an animal's distribution and abundance is environmental temperature. This factor affects all the components of an organism's energy budget and fitness. In this study, we tested the effect of water temperature and starvation on patterns of space use in the intertidal fish Girella laevifrons. We postulated that starved animals would select cold temperatures as a mechanism of energy conservation while fed animals would prefer higher temperatures as a mechanism to facilitate digestive processes. In a thermal gradient tank, fishes, irrespective of treatment (fed and starved), actively selected temperatures between 15 and 18 degrees C. Starvation did not affect temperature selection, although it did alter the time and number of visits to thermal gradient extremes. Starved fishes stayed longer in, and visited the warmer temperatures of the gradient more frequently. In contrast, fed fishes stayed longer in, and visited cold temperatures more frequently. We discuss the ecological consequences of temperature selection and the possible relationship between water temperature, food selection and digestive processes.
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    Behavioural thermoregulation in Acyrthosiphon pisum (Homoptera: Aphididae)
    (2001) Lagos, NA; Fuentes-Contreras, E; Bozinovic, F; Niemeyer, HM
    The effects of parasitisation by Aphidius ervi on the thermoregulatory behaviour of the pea aphid Acyrtosiphon pisum were studied in alfalfa fields and in an experimental thermal gradient. In the field, mummies were found exclusively on the adaxial surface of the upper leaves, and aphids in the mid canopy. The adaxial surface of the upper leaves was ca, 2 degreesC hotter that the mid-canopy, In the thermal gradient, the thermal effect (selected minus exposure temperature) was higher in magnitude in non-parasitised than in parasitised aphids; the thermal effects of both types of aphids were linearly and negatively correlated with exposure temperature (i.e. aphids showed negative thermal sensitivity), The thermal sensitivity of parasitised aphids was lower than that of non-parasitised aphids. The results are discussed in relation to hypotheses on factors governing the host-parasite relationship. (C) 2001 Elsevier Science Ltd. All rights reserved.
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    Communal burrowing in the hystricognath rodent, Octodon degus
    (2000) Ebensperger, LA; Bozinovic, F
    We examined the hypothesis that a main benefit of group-living in the semifossorial rodent, Octodon degus (Rodentia: Octodontidae), is to decrease individual cost of burrow construction. We contrasted the digging behavior of groups of three same-sex, adult-sized individuals with that of solitary degus. The behavior of singles and trios was recorded inside a large terrarium partially filled with natural soil and under controlled conditions of food, light, and temperature. The observation that degus in groups do not decrease their burrowing time or frequency of digging compared with solitary diggers does not support the hypothesis that communal burrowing is a primary cause of degu sociality. On the other hand, the observation that degus in groups removed significantly more soil per capita than solitary digging degus, and that grouped individuals coordinated their digging - group members burrowed mostly in the same sites and formed digging chains -, suggests that social burrowing may potentially reduce the cost of burrow construction in the long term. We suggest that such longterm benefits will be a consequence rather than a cause of degu group-living.
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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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    Diet selection in rodents: An experimental test of the effect of dietary fiber and tannins on feeding behavior
    (1997) Bozinovic, F
    The individual effects of chemical plant defenses on food preferences in small mammals have been explored in many studies. However, the combined effects of dietary fiber and tannins on feeding preference have received considerably less attention. Here I search for differences in feeding behavior of alternative experimental diets differing in fiber (cellulose = F) and a secondary metabolite (the hydrolyzable tannin, tannic acid = TA) in two sympatric rodent species that live in the Mediterranean environments of central Chile. I used the herbivorous burrowing caviomorph rodent Octodon degus (specialist), and the granivorous Sigmodontine Phyllotis darwini (generalist). These species differ in their trophic niche, and likely in behavioral and physiological features to cope with plant defenses. In preference trials with isocaloric diets, both species prefered dietary items with low F and TA. I conclude that non-energetic dietary features influence feeding strategies, and that generalist and specialist species behave in the same way. Future studies dealing with the ecology of foraging on chemical plant defenses should focus more explicitly on the interactive effect of different plant defensive compounds instead of on the isolated effect of single factors.
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    Digestive morphology and enzyme activity in the Andean toad, Bufo spinulosus
    (2005) Naya, DE; Farfán, G; Sabat, P; Méndez, MA; Bozinovic, F
    Gut plasticity is a trait with implications on animal performance. However, and despite their importance as study models in physiology, research on gut flexibility in amphibians is scarce. In the present work, we analyse digestive adjustments of Bufo spinulosus adult individuals to cope with changes in diet quality and quantity at two organizational levels (i.e., digestive morphology and enzymes). We found that changes in gut:size are related to the amount of food ingested, but not to diet composition. This is in agreement with "the gut seasonal change" hypothesis and offers a proximal explanation for this change. Digestive enzymatic activity (maltase and aminopeptidase-N) did not change with diet quality or quantity, which agrees with the hypothesis of "bard-wired physiology in adult amphibians". Both hypotheses are in agreement with the general theoretical framework of gut phenotypic flexibility when interpreted in light of amphibian natural history. In addition, our results indicate that the correlation between feeding frequency and the level of gut up-regulation proposed for interspecific comparisons may also be found at the intraspecific level. (c) 2004 Elsevier Inc. All rights reserved.
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    Digestive plasticity and the cost of acclimation to dietary chemistry in the omnivorous leaf-eared mouse Phyllotis darwini
    (2000) Sabat, P; Bozinovic, F
    We examined the costs associated with acclimation in an omnivorous mouse (Phyllotis darwini) fed two contrasting diets (carbohydrate-rich and protein-rich). We studied the response of gut morphology and digestive performance in animals shifted to a novel diet at different developmental stages. When acclimated adult animals were shifted to the alternative diet, energy digestibility decreased. We also found long-term consequences to diet acclimation. Animals reacclimated for 15 days to an alternative diet did not increase digestive performance. Although no effects of diet on gut morphology were noted, a significant positive correlation between energy digestibility and small intestinal length was found, explaining most of the variability observed in energy digestibility. These results suggest that caution should be used when defining adaptive changes if the possible cost of acclimation is neglected.
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    Does digestion rate affect diet selection? A study in Octodon degus, a generalist herbivorous rodent
    (1998) Bozinovic, F; Torres-Contreras, H
    Dietary chemistry and an animal digestive physiology should be considered in any explanation of behavioral patterns of food use, as both influence dietary preference. In the degu Octodon degus (Molina, 1782), a generalist herbivorous rodent inhabiting central Chile, we determine the profitablity of natural food-plant items by measuring digestive characteristics, such as retention time and assimilation rate while also considering the effects of food chemistry. Under our experimental conditions, degus seem to select food based on at least two complementary factors, plant nutritional value (water content and the nitrogen:fiber ratio) and digestive function. We found that dry-matter intake was negatively and significantly correlated with mean retention time, that is O. degus ate more food when mean retention time was shorter and vice versa. A higher food intake concomitant with a shorter mean retention time, allow degus to process more food per unit time resulting in a higher assimilation rate than alternative food sources. We conclude that both food quality and the digestive physiology of animals should be considered in explaining the underlying processes of foraging ecology.
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    Does food quality influence thermoregulatory behavior in the intertidal fish Girella laevifrons?
    (2003) Pulgar, JM; Aldana, M; Bozinovic, F; Ojeda, FP
    Algal and invertebrate species are less abundant towards higher zones of the intertidal, where the greatest variations in physical environmental conditions occur. Mobile predators such as fishes that inhabit high intertidal rockpools are thus exposed to wide variations in physical conditions and to a low abundance and quality of food. We used an aquarium with a temperature gradient in the laboratory to assesed whether dietary quality differences modify temperature preferences of Girella laevifrons, one of the most abundant transitory fishes inhabiting rocky shores along the coast of Chile. Our results indicate that food quality clearly modifies temperature preferences in this species. Animals fed on high quality bivalves selected intermediate temperatures (16-18degreesC) while those fed on lower quality algae selected lower temperatures (10-12degreesC). Control fish not subjected to the temperature gradient did not select portions of the aquarium differentially. The thermal selectivity of G. laevifons in relation to the optimization of digestive processes and mechanisms of energy conservation are discussed. (C) 2003 Elsevier Ltd. 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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    Dynamic energy and time budgets in hummingbirds
    (2003) López-Calleja, MV; Bozinovic, F
    Temperature and diet quality are two of the most important factors affecting the dynamic regulation of animal energy budgets. Because hummingbirds are very sensitive to energy stress, we used Green-backed Firecrowns (Sephanoides sephaniodes) to test the dynamics of their energy budget under different energetic challenges in chronic conditions (20 days). Experimental groups were: HQ-TNZ (high quality diet and thermoneutrality), HQ-LT (high quality diet and low temperature), LQ-TNZ (low quality diet and thermoneutrality), and LQ-LT (low quality diet and low temperature). Analysis of behavioral, morphological, and physiological variables revealed that thermal and dietary factors affect time and energy budgets independently. Hummingbirds increased energy intake during the first day of acclimation at LT, but after second day, the LQ-LT group did not maintain their energy intake and began to loose body mass. Moreover, diet quality affected digestive organs. The intestine, gizzard, liver and kidneys all increased in size when food quality was lowest, probably to obtain more food per feeding event and to more efficiently process the ingested food. Exposure to low ambient temperatures affected the most metabolically productive organs such as the heart, lungs, and muscular mass. Lower temperature increased basal and daily energy expenditure, and changed the time budget. Sephanoides sephaniodes spent more time perching when their energy balance was close to be negative. We suggest that energy budget regulation in hummingbirds does not reside exclusively in the energy output nor in the energy-input but in both pathways. (C) 2002 Elsevier Science Inc. 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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    Effect of food quality on the energetics of reproduction in a precocial rodent, Octodon degus
    (2000) Veloso, C; Bozinovic, F
    We examined the effect of food quality on ingestion, digestion, and metabolic rate during pregnancy and lactation in Octodon degus, a precocial rodent, under laboratory conditions. We also examined standard energetics during reproduction in relation to litter size and litter mass. Resting metabolic rate increased significantly during lactation, and that increase resulted from variations in food quality. The highest increase (39%) in resting metabolic rate was found in lactating females maintained on high-quality food when compared with nonreproductive females. Although food intake was always higher during lactation, the maximum intake was observed among lactating females that were given high-quality food. A significant positive correlation also was found between resting metabolic rate and food intake during early lactation, which revealed an increase in energy processing during that demanding period. Significant positive relationships also were found between resting metabolic and ingestion rate relative to litter mass and size. Allocation of energy in O, degus during lactation did not follow the mode typical of precocial rodents. En contrast, conversion efficiency of metabolizable energy into tissue growth appears to be linked to environmental quality of food.
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    Energetics and burrowing behaviour in the semifossorial degu Octodon degus (Rodentia: Octodontidae)
    (2000) Ebensperger, LA; Bozinovic, F
    The energetics and burrowing behaviour of the semifossorial Octodon degus (Rodentia: Octodontidae) were investigated and compared with that of more specialized fossorial rodents. An open-flow respirometry system was used to record energy expenditure of single degus inside respirometers partially filled with soft (moist) or hard (dry) soil. In addition, digging behaviour was recorded in groups of three animals inside a large terrarium under controlled conditions of food, photoperiod and temperature. In the field, the digging activity of degus was monitored, along with seasonal variations in rainfall, content of soil moisture and soil hardness. Mass-specific metabolic rate during digging was found to be higher in animals burrowing in soft soils compared to hard soil. However, animals burrowing in soft soil removed more soil per min than animals in hard soil. Thus, gram per gram, excavating in hard soil was energetically more expensive. The digging cost of semifossorial degus tends to be either similar to or above those of similarly sized, but more fossorial, rodents. In the field, heightened digging activity coincided with the occurrence of rainfall, greater content of soil moisture and relatively soft soil conditions. Degus generally use their front feet and teeth to sheer the soil; disposal of accumulated debris being carried out by moving their front and hind feet backwards. We also observed the establishment of digging chains when two or three individuals burrowed at the same site. As far as digging is concerned, the behaviour of degus is similar to that of other fossorial rodents, such as African bathyergids and the more closely related South American ctenomyids.
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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.