Living with voracious roommates: Factors that explain isotopic niche variation in a mixed colony of insectivorous bats.

Theory predicts that in resource-limited environments, coexisting species may overlap their niche dimensions but must differ in at least one to avoid competitive exclusion. Specifically, it has been suggested that the coexistence of competing species within a guild, could be sustained with mechanisms of resource partitioning, such as segregation along a trophic dimension. Among the most gregarious mammals are bats, which present diversification in their diet based on habitat choice and body size. Despite differences that could explain specialization in prey selection, there are insufficient studies that explore food overlap in mixed bat colonies and the factors that determine the selection of prey, both at intra- and inter-specific levels. To fill this gap, we analyzed the isotope signal (δ13C and δ15N) in feces collected in a mixed colony of Tadarida brasiliensis and Myotis chiloensis. To understand how several factors could influence these isotopic signals, intrinsic explanatory variables were analyzed, including body mass, body length, age, and sex. Also, extrinsic variables were analyzed, including monthly temporality and moonlight intensity. Our findings support age-dependent specialization in M. chiloensis, with a significant role of moonlight intensity and sex on δ15N. In T. brasiliensis, we identified a significant effect of size, sex, and ear length on δ15N. Our analysis indicates that both species of bats experience diverse degrees of overlap through austral summer months, affected by several factors that explain the variability in their fecal isotopic signals.

The effects of urban thermal heterogeneity and feather coloration on oxidative stress and metabolism of pigeons (Columba livia).

Urbanization stands out as a significant anthropogenic factor, exerting selective pressures on ecosystems and biotic components. A notable outcome of urbanization is thermal heterogeneity where the emergence of Urban Heat Islands is characterized by elevated air and surface temperatures compared to adjacent rural areas. Investigating the influence of thermal heterogeneity on urban animals could offer insights into how temperature variations can lead to phenotypic shifts. Urban pigeons (Columba livia) serve as an excellent model for studying urban thermal effects, given the melanism variations, which are associated with the pleiotropy of the melanocortin system. To examine the development of physiological plasticity in response to urban thermal variations, we conducted a study on pigeons in Santiago, Chile, during the rainy season. We assessed the influence of habitat on physiological traits related to metabolism and antioxidant capacities, which are theoretically affected by feather coloration. Our findings reveal that variations in melanism significantly impact pigeon physiology, affecting both antioxidant capacities and the mitochondrial activity of red blood cells. It was found that higher urban temperatures, from both the current sampling month and the prior sampling month (from CRU TS dataset), were negatively and strongly associated with lower antioxidant and metabolic activities. This suggests that elevated urban temperatures likely benefit the energetic budgets of pigeon populations and mitigate the negative effects of oxidative metabolism, with differential effects depending on feather colorations.

Seasonal changes in diet, immune function, and oxidative stress in three passerines inhabiting a Mediterranean climate.

Oxidative status and immune function are energy-demanding traits closely linked to diet composition, particularly resource availability and nutritional value. In seasonal environments, nutrient availability and diet quality fluctuate, potentially influencing these traits. However, limited evidence exists regarding these dietary effects on immune function in seasonal environments. In this study, we employed stable isotope analysis to assess the impact of seasonal changes in niche width and trophic level (i.e., δ15N) on two immune variables (hemolysis and hemagglutination scores) and two oxidative status parameters (lipid peroxidation and total antioxidant capacity) in three passerine species: Zonotrichia capensis (omnivorous), Troglodytes aedon (insectivorous), and Spinus barbatus (granivorous). We found that hemolysis scores varied seasonally in Z. capensis, with higher values in winter compared to summer. Total antioxidant capacity (TAC) also increased during the winter in Z. capensis and S. barbatus. The isotopic niche width for Z. capensis and S. barbatus was smaller in winter than in summer, with the omnivorous species exhibiting a decrease in δ15N. Despite the seasonal shifts in ecological and physiological traits in Z. capensis, we identified no correlation between immune response and TAC with trophic level. In contrast, in the granivorous S. barbatus, the lower trophic level resulted in an increase in TAC without affecting immunity. Our findings revealed that dietary shifts do not uniformly impact oxidative status and immune function across bird species, highlighting species-specific responses to seasonal changes. This underscores the importance of integrating ecological and evolutionary perspectives when examining how diet shapes avian immunity and oxidative balance.

Modeling heterothermic fitness landscapes in a marsupial hibernator using changes in body composition.

Hibernation is an adaptive strategy that allows animals to enter a hypometabolic state, conserving energy and enhancing their fitness by surviving harsh environmental conditions. However, addressing the adaptive value of hibernation, at the individual level and in natural populations, has been challenging. Here, we applied a non-invasive technique, body composition analysis by quantitative magnetic resonance (qMR), to calculate energy savings by hibernation in a population of hibernating marsupials (Dromiciops gliroides). Using outdoor enclosures installed in a temperate rainforest, and measuring qMR periodically, we determined the amount of fat and lean mass consumed during a whole hibernation cycle. With this information, we estimated the daily energy expenditure of hibernation (DEEH) at the individual level and related to previous fat accumulation. Using model selection approaches and phenotypic selection analysis, we calculated linear (directional, ß), quadratic (stabilizing or disruptive, γ) and correlational (ρ) coefficients for DEEH and fat accumulation. We found significant, negative directional selection for DEEH (ßDEEH = - 0.58 ± 0.09), a positive value for fat accumulation (ßFAT = 0.34 ± 0.07), and positive correlational selection between both traits (ρDEEH × FAT = 0.24 ± 0.07). Then, individuals maximizing previous fat accumulation and minimizing DEEH were promoted by selection, which is visualized by a bi-variate selection surface estimated by generalized additive models. At the comparative level, results fall within the isometric allometry known for hibernation metabolic rate in mammals. Thus, by a combination of a non-invasive technique for body composition analysis and semi-natural enclosures, we were characterized the heterothermic fitness landscape in a semi-natural population of hibernators.

Prenatal caloric restriction adjusts the energy homeostasis and behavior in response to acute and chronic variations in food availability in adulthood.

Fetal metabolic programming produced by unfavorable prenatal nutritional conditions leads to the development of a disorder called "thrifty phenotype", which is associated with pathologies such as diabetes and obesity in adulthood. However, from an ecophysiological approach, few studies have addressed the development of thrifty phenotypes in terms of energy. This might represent an adaptive advantage against caloric deficiency conditions extending into adulthood. The objective of this study is to investigate the potential adaptive value of the thrifty phenotype expression through prenatal programming in a rodent model experiencing varying dietary conditions in different temporal contexts. To fill this gap, adult males of Mus musculus (BALB/C) from two maternal pregnancy groups were analyzed: control (ad libitum feeding) and caloric restriction from day 10 of gestation (70% restriction). Adult offspring of these groups were split further for two experiments: acute food deprivation and chronic caloric restriction at 60%. The acute food deprivation was performed for 24, 48 or 72 h while the caloric restriction regime was sustained for 20 days. For each experiment, morphological variables, such as body and organ mass, and gene expression related to lipid and carbohydrate metabolism from the liver and brain, were evaluated. In chronic caloric restriction, behavioral tests (open-field test and home-cage behavior) were performed. Our results indicate that under acute deprivation, the liver mass and triglyceride content remained unchanged in individuals subjected to prenatal restriction, in contrast to the reduction experienced by the control group. The latter is associated with the expression of the key genes involved in energy homeostasis (Pepck, Pparα/Pparγ), indicating a differential use of nutritional resources. In addition, thrifty animals, subjected to chronic caloric restriction, showed a severe reduction in locomotor and gluconeogenic activity, which is consistent with the regulatory role of Sirt1 and its downstream targets Mao and Pepck. Our results reveal that prenatal caloric restriction translates into a sparing metabolism in response to acute and chronic lack of food in adulthood.

Geographic variation in the altitudinal migration patterns, body size, oxidative status and exploratory behavior in a neotropical bird.

To cope with life in the mountains, populations of the same species can exhibit substantial variability in their altitudinal migration patterns and phenotypes in response to local weather conditions. Studying such variability can provide valuable insights into how local populations respond to environmental challenges, and this information can be useful for conservation efforts in mountain ecosystems. Here, we used δ2H values of feathers and blood to evaluate latitudinal variation in altitudinal migration patterns and its possible links with body size, oxidative status, and exploratory behavior in 72 individuals of rufous-collared sparrow (Zonotrichia capensis) that breed at low and high elevations in the center (~33°) and south (~38°) of Chile. Our results show that both altitudinal migration patterns and oxidative status were significantly influenced by the latitude of breeding sites, while exploratory behavior was associated with elevation. Notably, we found that fast-explorer birds inhabiting low elevations in central Chile displayed higher levels of oxidative damage than slow-explorer birds. These outcomes underscore the possibility of local adaptations in response to diverse local environmental conditions in the Andes. We discuss the implications of latitude, elevation, and environmental temperature in shaping the observed patterns and highlight the significance of identifying local adaptations in mountain birds for better predicting their response to climate change and other challenges stemming from anthropogenic activities.

Predicting the bioremediation potential of earthworms of different ecotypes through a multi-biomarker approach.

Earthworms are attracting the attention of bioremediation research because of their short-term impact on pollutant fate. However, earthworm-assisted bioremediation largely depends on the earthworm sensitivity to target pollutants and its metabolic capacity to break down contaminants. The most studied species in soil bioremediation has been Eisenia fetida, which inhabits the soil surface feeding on decomposing organic residues. Therefore, its bioremediation potential may be limited to organic matter-rich topsoil. We compared the detoxification potential against organophosphate (OP) pesticides of three earthworm species representative of the main ecotypes: epigeic, anecic, and endogeic. Selected biomarkers of pesticide detoxification (esterases, cytochrome P450-dependent monooxygenase, and glutathione S-transferase) and oxidative homeostasis (total antioxidant capacity, glutathione levels, and glutathione reductase [GR] and catalase activities) were measured in the muscle wall and gastrointestinal tract of E. fetida (epigeic), Lumbricus terrestris (anecic) and Aporrectodea caliginosa (endogeic). Our results show that L. terrestris was the most suitable species to bioremediate OP-contaminated soil for the following reasons: 1) Gut carboxylesterase (CbE) activity of L. terrestris was higher than that of E. fetida, whereas muscle CbE activity was more sensitivity to OP inhibition than that of E. fetida, which means a high capacity to inactivate the toxic oxon metabolites of OPs. 2) Muscle and gut phosphotriesterase activities were significantly higher in L. terrestris than in the other species. 3) Enzymatic (catalase and GR) and molecular mechanisms of free radical inactivation (glutathione) were 3- to 4-fold higher in L. terrestris concerning E. fetida and A. caliginosa, which reveals a higher potential to keep the cellular oxidative homeostasis against reactive metabolites formed during OP metabolism. Together with biological and ecological traits, these toxicological traits suggest L. terrestris a better candidate for soil bioremediation than epigeic earthworms.

Synergistic effects of pesticides and environmental variables on earthworm standard metabolic rate.

Endogeic earthworms such as Aporrectodea caliginosa play an essential role in the agroecosystems because of their continuous burrowing and feeding (geophagous) activity, which causes a profound impact on soil texture, organic matter decomposition, soil carbon storage, microbial activity, soil biodiversity, and nutrient cycling. Accordingly, endogeic earthworms are being proposed as suitable candidates for the ecotoxicity assessment of polluted soils. However, terrestrial ecotoxicology has little considered the interactive effects from pollutants and environmental variables (temperature, moisture). We acclimatized A. caliginosa for 90 days to two contrasting temperatures (10 °C and 20 °C) and moistures (25 % and 35 %, w/v) in soils contaminated with 20 mg kg-1 of chlorpyrifos to examine how these two climate change drivers may modulate the pesticide toxicity. We measured the inhibition of cholinesterase (ChE) activities as indicators of organophosphorus exposure, the standard metabolic rate as an integrative physiological biomarker, and the lipid peroxidation (TBARS) and the total antioxidant capacity (TAC) both as indicators of oxidative stress. The main results were: i) chlorpyrifos strongly inhibited ChE activity (>75 % of controls), demonstrating earthworm bioavailability and acute toxicity at the test concentration; 2) a 50 % mortality and loss of body weight (49 %) were found in the earthworms exposed to the most severe environmental conditions (20 °C, 25 %, and pesticide); 3) this latter experimental group displayed a high SMR, which was concomitant with an increase of the oxidative balance index (TBARS/TAC). We postulated that earthworms acclimatized to stressing environmental conditions experienced a higher pesticide-induced metabolic cost and physiological challenges imposed by adverse environmental conditions.

Biochemical and osmoregulatory responses of the African clawed frog experimentally exposed to salt and pesticide.

Salinization and pollution are two main environmental stressors leading deterioration to water quality and degradation of aquatic ecosystems. Amphibians are a highly sensitive group of vertebrates to environmental disturbance of aquatic ecosystems. However, studies on the combined effect of salinization and pollution on the physiology of amphibians are limited. In this study, we measured the standard metabolic rate (SMR) and biochemical parameters of adult males of the invasive frog Xenopus laevis after 45 days of exposure to contrasting salinity environments (400 and 150 mOsm NaCl) with either 1.0 µg/L of the organophosphate pesticide chlorpyrifos (CPF) or pesticide-free medium. Our results revealed a decrease in SMR of animals exposed to the pesticide and in the ability to concentrate the plasma in animals exposed simultaneously to both stressors. The lack of ability to increase plasma concentration in animals exposed to both salt water and CPF, suggests that osmoregulatory response is decreased by pesticide exposure. In addition, we found an increase of liver citrate synthase activity in response to salt stress. Likewise, the liver acetylcholinesterase (AChE) activity decreased by 50% in frogs exposed to salt water and CPF and 40% in those exposed only to CPF, which suggest an additive effect of salinity on inhibition of AChE. Finally, oxidative stress increased as shown by the higher lipid peroxidation and concentration of aqueous peroxides found in the group exposed to salt water and pesticide. Thus, our results revealed that X. laevis physiology is compromised by salinization and pesticide exposure to both environmental stressors join.

Body Composition and Energy Savings by Hibernation: Lessons from the South American Marsupial Dromiciops gliroides.

AbstractHibernation (i.e., seasonal or multiday torpor) has been described in mammals from five continents and represents an important adaptation for energy economy. However, direct quantifications of energy savings by hibernation are challenging because of the complexities of estimating energy expenditure in the field. Here, we applied quantitative magnetic resonance to determine body fat and body composition in hibernating Dromiciops gliroides (monito del monte). During an experimental period of 31 d in winter, fat was significantly reduced by 5.72±0.45 g, and lean mass was significantly reduced by 2.05±0.14 g. This fat and lean mass consumption is equivalent to a daily energy expenditure of hibernation (DEEH) of 8.89±0.6 kJ d-1, representing 13.4% of basal metabolic rate, with a proportional contribution of fat and lean mass consumption to DEEH of 81% and 18%, respectively. During the deep heterothermic bouts of monitos, body temperature remained 0.41°C ± 0.2°C above ambient temperature, typical of hibernators. Animals shut down metabolism and passively cool down to a critical defended temperature of 5.0°C ± 0.1°C, where they begin thermoregulation in torpor. Using temperature data loggers, we obtained an empirical estimation of minimum thermal conductance of 3.37±0.19 J g-1 h-1 °C-1, which is 107% of the expectation by allometric equations. With this, we parameterized body temperature/ambient temperature time series to calculate torpor parameters and metabolic rates in euthermia and torpor. Whereas the acute metabolic fall in each torpor episode is about 96%, the energy saved by hibernation is 88% (compared with the DEE of active animals), which coincides with values from the literature at similar body mass. Thus, estimating body composition provides a simple method to measure the energy saved by hibernation in mammals.

The ecology and evolution of the monito del monte, a relict species from the southern South America temperate forests.

The arboreal marsupial monito del monte (genus Dromiciops, with two recognized species) is a paradigmatic mammal. It is the sole living representative of the order Microbiotheria, the ancestor lineage of Australian marsupials. Also, this marsupial is the unique frugivorous mammal in the temperate rainforest, being the main seed disperser of several endemic plants of this ecosystem, thus acting as keystone species. Dromiciops is also one of the few hibernating mammals in South America, spending half of the year in a physiological dormancy where metabolism is reduced to 10% of normal levels. This capacity to reduce energy expenditure in winter contrasts with the enormous energy turnover rate they experience in spring and summer. The unique life history strategies of this living Microbiotheria, characterized by an alternation of life in the slow and fast lanes, putatively represent ancestral traits that permitted these cold-adapted mammals to survive in this environment. Here, we describe the ecological role of this emblematic marsupial, summarizing the ecophysiology of hibernation and sociality, updated phylogeographic relationships, reproductive cycle, trophic relationships, mutualisms, conservation, and threats. This marsupial shows high densities, despite presenting slow reproductive rates, a paradox explained by the unique characteristics of its three-dimensional habitat. We finally suggest immediate actions to protect these species that may be threatened in the near future due to habitat destruction and climate change.

A Mesocosm Experiment in Ecological Physiology: The Modulation of Energy Budget in a Hibernating Marsupial under Chronic Caloric Restriction.

AbstractDuring the past 60 years, mammalian hibernation (i.e., seasonal torpor) has been interpreted as a physiological adaptation for energy economy. However, direct field comparisons of energy expenditure and torpor use in hibernating and active free-ranging animals are scarce. Here, we followed the complete hibernation cycle of a fat-storing hibernator, the marsupial Dromiciops gliroides, in its natural habitat. Using replicated mesocosms, we experimentally manipulated energy availability and measured torpor use, hibernacula use, and social clustering throughout the entire hibernation season. Also, we measured energy flow using daily food intake, daily energy expenditure (DEE), and basal metabolic rate (BMR) in winter. We hypothesized that when facing chronic caloric restriction (CCR), a hibernator should maximize torpor frequency to compensate for the energetic deficit, compared with individuals fed ad lib. (controls). However, being torpid at low temperatures could increase other burdens (e.g., cost of rewarming, freezing risks). Our results revealed that CCR animals, compared with control animals, did not promote heat conservation strategies (i.e., clustering and hibernacula use). Instead, they gradually increased torpor frequency and reduced DEE and, as a consequence, recovered weight at the end of the season. Also, CCR animals consumed food at a rate of 50.8 kJ d-1, whereas control animals consumed food at a rate of 98.4 kJ d-1. Similarly, the DEE of CCR animals in winter was 47.3±5.64 kJ d-1, which was significantly lower than control animals (DEE=88.0±5.84 kJ d-1). However, BMR and lean mass of CCR and control animals did not vary significantly, suggesting that animals maintained full metabolic capacities. This study shows that the use of torpor can be modulated depending on energy supply, thus optimizing energy budgeting. This plasticity in the use of heterothermy as an energy-saving strategy would explain the occurrence of this marsupial in a broad latitudinal and altitudinal range. Overall, this study suggests that hibernation is a powerful strategy to modulate energy expenditure in mammals from temperate regions.

Approaching the Ecological Role of the Squat Lobster (Munida gregaria) and the Fuegian Sprat (Sprattus fuegensis) in the Francisco Coloane Marine Area (Magellan Strait, Chile) Using a Pelagic Food Web Model.

The structure and functioning of the food web of the Francisco Coloane Marine Area in the Magellan Strait, Chile, was quantified, with an emphasis on identifying the ecological role of the squat lobster (Munida gregaria) and the Fuegian sprat (Sprattus fuegensis). Food web indicators, the trophic level, and centrality indices were estimated using Ecopath with Ecosim. Dynamic simulations were carried out to evaluate the ecosystem impacts of biomass changes in squat lobster and Fuegian sprat. The model calculated a total ecosystem biomass of 71.7 t km-2 and a total primary production of 2450.9 t km-2 year-1. Squat lobster and Fuegian sprat were located in specific trophic levels of 2.3 and 2.7, respectively. Squat lobster reduction produced a decrease in the biomass of red cod (42-56%) and humpback whales (25-28%) and Fuegian sprat reduction a decrease in penguins (15-37%) and seabirds (11-34%). The Francisco Coloane Area is an immature ecosystem with productivity and energy flows values within those reported for productive ecosystems; the role of the squat lobster seems to be related to the structure of the food web, and the role of the Fuegian sprat seems to be related to the functioning of the ecosystem and to the energy transfer to top predators.

Perinatal Food Deprivation Modifies the Caloric Restriction Response in Adult Mice Through Sirt1.

Variations in the availability of nutritional resources in animals can trigger reversible adjustments, which in the short term are manifested as behavioral and physiological changes. Several of these responses are mediated by Sirt1, which acts as an energy status sensor governing a global genetic program to cope with changes in nutritional status. Growing evidence suggests a key role of the response of the perinatal environment to caloric restriction in the setup of physiological responses in adulthood. The existence of adaptive predictive responses has been proposed, which suggests that early nutrition could establish metabolic capacities suitable for future food-scarce environments. We evaluated how perinatal food deprivation and maternal gestational weight gain impact the transcriptional, physiological, and behavioral responses in mice, when acclimated to caloric restriction in adulthood. Our results show a strong predictive capacity of maternal weight and gestational weight gain, in the expression of Sirt1 and its downstream targets in the brain and liver, mitochondrial enzymatic activity in skeletal muscle, and exploratory behavior in offspring. We also observed differential responses of both lactation and gestational food restriction on gene expression, thermogenesis, organ masses, and behavior, in response to adult caloric restriction. We conclude that the early nutritional state could determine the magnitude of responses to food scarcity later in adulthood, mediated by the pivotal metabolic sensor Sirt1. Our results suggest that maternal gestational weight gain could be an important life history trait and could be used to predict features that improve the invasive capacity or adjustment to seasonal food scarcity of the offspring.

Triple Oxygen Isotope Measurements (Δ'17O) of Body Water Reflect Water Intake, Metabolism, and δ18O of Ingested Water in Passerines.

Understanding physiological traits and ecological conditions that influence a species reliance on metabolic water is critical to creating accurate physiological models that can assess their ability to adapt to environmental perturbations (e.g., drought) that impact water availability. However, relatively few studies have examined variation in the sources of water animals use to maintain water balance, and even fewer have focused on the role of metabolic water. A key reason is methodological limitations. Here, we applied a new method that measures the triple oxygen isotopic composition of a single blood sample to estimate the contribution of metabolic water to the body water pool of three passerine species. This approach relies on Δ'17O, defined as the residual from the tight linear correlation that naturally exists between δ17O and δ18O values. Importantly, Δ'17O is relatively insensitive to key fractionation processes, such as Rayleigh distillation in the water cycle that have hindered previous isotope-based assessments of animal water balance. We evaluated the effects of changes in metabolic rate and water intake on Δ'17O values of captive rufous-collared sparrows (Zonotrichia capensis) and two invertivorous passerine species in the genus Cinclodes from the field. As predicted, colder acclimation temperatures induced increases in metabolic rate, decreases in water intake, and increases in the contribution of metabolic water to the body water pool of Z. capensis, causing a consistent change in Δ'17O. Measurement of Δ'17O also provides an estimate of the δ18O composition of ingested pre-formed (drinking/food) water. Estimated δ18O values of drinking/food water for captive Z. capensis were ~ -11‰, which is consistent with that of tap water in Santiago, Chile. In contrast, δ18O values of drinking/food water ingested by wild-caught Cinclodes were similar to that of seawater, which is consistent with their reliance on marine resources. Our results confirm the utility of this method for quantifying the relative contribution of metabolic versus pre-formed drinking/food water to the body water pool in birds.

Nutritional ecology and ecological immunology in degus: Does early nutrition affect the postnatal development of the immune function?

Environmental conditions experienced by developing animals have an impact on the development and maturity of the immune system. Specifically, the diet experienced during early development influences the maintenance and function of the immune system in young and adult animals. It is well known that exposure to low-protein diets during early development are related to an attenuation of immunocompetence in adulthood. While this functional linkage has been widely studied in altricial models' mammals, it has been little explored how the nutritional history modulates the immune function in precocial animals. We evaluated the effect of dietary protein consumed during early development on the immune function and the oxidative costs in the precocial Caviomorph rodent Octodon degus, or degu. We evaluated components of the acute phase response (APR) and oxidative parameters before and after immune challenge. We found that after the immune challenge, the juveniles on the low-protein dietary treatment exhibited an attenuation of body temperature but showed higher levels of lipid peroxidation than juvenile degus on the high-protein diet. We did not find a significant effect of the interaction between diet and immune challenge on body mass, levels of inflammatory proteins, nor in the total antioxidant capacity. Our results suggest that some components of the immune function and the oxidative status in the degu can be modulated by diet during development. However, the modulation would depend on the immune variables analyzed, and the characteristics of the immune system of precocial rodents.

Latitudinal patterns in the diet of Andean condor (Vultur gryphus) in Chile: Contrasting environments influencing feeding behavior.

Human-dominated environments alter the availability and quality of resources for many species, especially for scavengers that have large home ranges and plastic foraging behaviors that enable them to exploit novel resources. Along the western slope of the Andes, the modification of natural landscapes have resulted in significant declines in native prey, the introduction of non-native species, and an increase in the availability of anthropogenic resources. These factors have likely influenced the resources available to Andean condors (Vultur gryphus), however, data are lacking as to how condor's diet vary along their large latitudinal range. We evaluated differences in Andean condor diet along a ~2500 km latitudinal gradient in Chile from the heavily modified Central zone (32-34°S) to the more pristine Austral zone (44-56°S). We assessed diet composition through the identification of prey remains in condor pellets, and carbon and nitrogen isotope analysis of condor feathers and their primary prey identified from pellet analysis. Our results identified medium- and large-bodied domesticated mammals (ungulates) and introduced exotic species (lagomorphs) as common prey across the study area. Condors from the Central zone had the largest isotopic niche width, probably related to consumption of anthropogenic resources with distinctly high carbon isotope values indicative of C4-based foods likely acquired from landfills or corn-fed livestock. Isotopic niches for condors from the Southern and Austral zones almost completely overlapped. Andean condor diet is strongly influenced by local conditions determining differential access to prey sources. The high dependence of Andean condors on livestock across a large geographical area, and landfills in more (sub)urban areas, may help stabilize their populations via anthropogenic resources subsidies. Long-term dependence on such resources, however, may have health costs including contaminant exposure and greater mortality risk. These data will help identify potential threats related to resource availability and use, and better inform management and conservation decisions.

New Pharmacological Strategies for the Treatment of Non-Infectious Uveitis. A Minireview.

Non-infectious uveitis (NIU) is a group of disorders characterized by intraocular inflammation at different levels of the eye. NIU is a leading cause of irreversible blindness in working-age population in the developed world. The goal of uveitis treatment is to control inflammation, prevent recurrences, and preserve vision, as well as minimize the adverse effects of medications. Currently, the standard of care for NIU includes the administration of corticosteroids (CS) as first-line agents, but in some cases a more aggressive therapy is required. This includes synthetic immunosuppressants, such as antimetabolites (methotrexate, mycophenolate mofetil, and azathioprine), calcineurinic inhibitors (cyclosporine, tacrolimus), and alkylating agents (cyclophosphamide, chlorambucil). In those patients who become intolerant or refractory to CS and conventional immunosuppressive treatment, biologic agents have arisen as an effective therapy. Among the most evaluated treatments, TNF-α inhibitors, IL blockers, and anti-CD20 therapy have emerged. In this regard, anti-TNF agents (infliximab and adalimumab) have shown the strongest results in terms of favorable outcomes. In this review, we discuss latest evidence concerning to the effectiveness of biologic therapy, and present new therapeutic approaches directed against immune components as potential novel therapies for NIU.

Effect of salinity acclimation on osmoregulation, oxidative stress, and metabolic enzymes in the invasive Xenopus laevis.

Aquatic animals often display physiological adjustments to improve their biological performance and hydrosaline balance in saline environments. In addition to energetic costs associated with osmoregulation, oxidative stress, and the activation of the antioxidant system are common cellular responses to salt stress in many species, but the knowledge of osmoregulation-linked oxidative homeostasis in amphibians is scarce. Here we studied the biochemical responses and oxidative responses of Xenopus laevis females exposed for 40 days to two contrasting salinities: hypo-osmotic (150 mOsm·kg-1 ·H2 O NaCl, HYPO group) and hyper-osmotic environments (340 mOsm·kg-1 ·H2 O NaCl, HYPER group). We found an increase of plasma osmolality and plasma urea concentration in the animals incubated in the HYPER treatment. Increases in electrolyte concentration were paralleled with an increase of both citrate synthase and cytochrome c oxidase activities in liver and heart. Interestingly, HYPO group had higher catabolic activity of the skin and liver total antioxidant capacity (TAC), compared with animals from the HYPER group. Moreover, there was an inverse relationship between liver TAC and plasma osmolality; and with the metabolic enzymes from liver. These findings suggest that salinity induces changes in urea metabolism and specific activity of metabolic enzymes, which appears to be tissue-dependent in X. laevis. Contrary to our expectations, we also found a moderate change in the oxidative status as revealed by the increase in TAC activity in the animals acclimated to low salinity medium, but constancy in the lipid peroxidation of membranes.

Costs of exploratory behavior: the energy trade-off hypothesis and the allocation model tested under caloric restriction.

In order to maintain the energy balance, animals often exhibit several physiological adjustments when subjected to a decrease in resource availability. Specifically, some rodents show increases in behavioral activity in response to food restriction; a response regarded as a paradox because it would imply an investment in locomotor activity, despite the lack of trophic resources. Here, we aim to explore the possible existence of trade-offs between metabolic variables and behavioral responses when rodents are faced to stochastic deprivation of food and caloric restriction. Adult BALB/c mice were acclimatized for four weeks to four food treatments: two caloric regimens (ad libitum and 60% restriction) and two periodicities (continuous and stochastic). In these mice, we analyzed: exploratory behavior and home-cage behavior, basal metabolic rate, citrate synthase and cytochrome oxidase c enzyme activity (in liver and skeletal muscle), body temperature and non-shivering thermogenesis. Our results support the model of allocation, which indicates commitments between metabolic rates and exploratory behavior, in a caloric restricted environment. Specifically, we identify the role of thermogenesis as a pivotal budget item, modulating the reallocation of energy between behavior and basal metabolic rate. We conclude that brown adipose tissue and liver play a key role in the development of paradoxical responses when facing decreased dietary availability.