Coping with Salt Water Habitats: Metabolic and Oxidative Responses to Salt Intake in the Rufous-Collared Sparrow.

Many physiological adjustments occur in response to salt intake in several marine taxa, which manifest at different scales from changes in the concentration of individual molecules to physical traits of whole organisms. Little is known about the influence of salinity on the distribution, physiological performance, and ecology of passerines; specifically, the impact of drinking water salinity on the oxidative status of birds has been largely ignored. In this study, we evaluated whether experimental variations in the salt intake of a widely-distributed passerine (Zontotrichia capensis) could generate differences in basal (BMR) and maximum metabolic rates (Msum), as well as affect metabolic enzyme activity and oxidative status. We measured rates of energy expenditure of birds after 30-d acclimation to drink salt (SW) or tap (fresh) water (TW) and assessed changes in the activity of mitochondrial enzymes (cytochrome c oxidase and citrate synthase) in skeletal muscle, heart, and kidney. Finally, we evaluated the oxidative status of bird tissues by means of total antioxidant capacity (TAC) and superoxide dismutase activities and lipid oxidative damage (Malondialdehyde, MDA). The results revealed a significant increase in BMR but not Msum, which resulted in a reduction in factorial aerobic scope in SW- vs. TW-acclimated birds. These changes were paralleled with increased kidney and intestine masses and catabolic activities in tissues, especially in pectoralis muscle. We also found that TAC and MDA concentrations were ~120 and ~400% higher, respectively in the liver of animals acclimated to the SW- vs. TW-treatment. Our study is the first to document changes in the oxidative status in birds that persistently drink saltwater, and shows that they undergo several physiological adjustments that range that range in scale from biochemical capacities (e.g., TAC and MDA) to whole organism traits (e.g., metabolic rates). We propose that the physiological changes observed in Z. capensis acclimated to saltwater could be common phenomena in birds and likely explain selection of prey containing little salt and habitats associated with low salinity.

Metabolic cost of osmoregulation in a hypertonic environment in the invasive African clawed frog Xenopus laevis.

Studies of aquatic invertebrates reveal that salinity affects feeding and growth rates, reproduction, survival, and diversity. Little is known, however, about how salinity impacts the energy budget of vertebrates and amphibians in particular. The few studies focused on this topic in vertebrates suggest that the ingestion of salts and the resulting osmoregulatory activity is energetically expensive. We analyzed the effect of saline acclimation on standard metabolic rates (SMR) and the activities of metabolic enzymes of internal organs and osmoregulatory variables (plasma osmolality and urea plasma level) in females of Xenopus laevis by means of acclimating individuals to an isosmotic (235 mOsm NaCl; ISO group) and hyper-osmotic (340 mOsm NaCl; HYP group) environment for 40 days. After acclimation, we found that total and mass-specific SMR was approximately 80% higher in the HYP group than those found in the ISO group. These changes were accompanied by higher citrate synthase activities in liver and heart in the HYP group than in the ISO group. Furthermore, we found a significant and positive correlation between metabolic rates and plasma urea, and citrate synthase activity in liver and heart. These results support the notion that the cost of osmoregulation is probably common in most animal species and suggest the existence of a functional association between metabolic rates and the adjustments in osmoregulatory physiology, such as blood distribution and urea synthesis.

Subchronic exposure to chlorpyrifos affects energy expenditure and detoxification capacity in juvenile Japanese quails.

Effects of pesticides on non-target organisms have been studied in several taxa at different levels of biological organization, from enzymatic to behavioral responses. Although the physiological responses may be associated with higher energy costs, little is known about metabolic costs of pesticide detoxification in birds. To fill this gap, we exposed orally (diet) 15-d old Coturnix coturnix japonica individuals to sublethal doses of chlorpyrifos (10 and 20 mg active ingredient/kg dry food) for four weeks. Carboxylesterase (CbE), butyrylcholinesterase (BChE) and acetylcholinesterase (AChE) activities were periodically measured in multiple tissues along with measurements of resting (RMR) and maximum metabolic rates (M(sum)). Furthermore, glucuronic acid in bird excreta was also assessed at the end of the trial. While CbE and BChE activities were inhibited by chlorpyrifos in all tissues during the third and fourth weeks following pesticide treatment, AChE activity was unaffected. At this sampling times, both M(sum) and RMR expansibility decreased. These results suggest that the exposure to chlorpyrifos caused a negative effect on aerobic performance. Additionally, excretion rate of glucuronic acid was up to 2-fold higher in the 20-mg/kg group than in the control and 10-mg/kg chlorpyrifos groups. The inhibition of CbE and BChE activities corroborated that these enzymes are fulfilling their role as bioscavengers for organophosphate pesticides, decreasing its concentration and thus protecting AChE activity against inhibition by chlorpyrifos.

Comparative intestinal esterases amongst passerine species: Assessing vulnerability to toxic chemicals in a phylogenetically explicit context.

Inhibition of blood esterase activities by organophosphate (OP) pesticides has been used as a sensitive biomarker in birds. Furthermore, compared to mammalian vertebrates, less is known about the role of these enzyme activities in the digestive tracts of non-mammalian vertebrates, as well as the environmental and biological stressors that contribute to their natural variation. To fill this gap, we examined butyrylcholinesterase (BChE) and carboxylesterases (CbE) in the digestive tracts of sixteen passerine species from central Chile. Whole intestine enzyme activities were positively and significantly correlated with body mass. After correcting for body mass and phylogenetic effect, we found only a marginal effect of dietary category on BChE activity, but a positive and significant association between the percentage of dietary nitrogen and the mass-corrected lipase activity. Our results suggest that observed differences may be due to the dietary composition in the case of lipases and BChE, and also we predict that all model species belonging to the same order will probably respond differently to pesticide exposure, in light of differences in the activity levels of esterase activities.

Feeding and digestive responses to fatty acid intake in two South American passerines with different food habits.

Specific fatty acids (FA) such as unsaturated (UFA) and saturated (SFA) fatty acids contained in foods are key factors in the nutritional ecology of birds. By means of a field and experimental approach, we evaluated the effect of diet on the activity of three esterases involved in FA hydrolysis; carboxylesterase (CE: 4-NPA-CE and a-NA-CE) and butyrylcholinesterase, in two South American passerines: the omnivorous rufous-collared sparrow (Zonotrichia capensis) and the granivorous common diuca-finch (Diuca diuca). The activity of the three esterases was measured in the intestines of freshly caught individuals over two distinct seasons and also after a chronic intake of a UFA-rich or SFA-rich diet in the laboratory. In turn, we assessed the feeding responses of the birds choosing amongst diets contrasting in the kind of specific FA (UFA- vs. SFA-treated diets). During summer, field CE activities (4-NPA-CE and a-NA-CE) in the small intestine were higher in the rufous-collared sparrow (25.3 ± 3.3 and 81.4 ± 10.8 µmol min(-1) g tissue(-1), respectively) than in the common diuca-finch (10.0 ± 3.0 and 33.9 ± 13.1 µmol min(-1) g tissue(-1), respectively). Two hour feeding trial test indicated that both species exhibited a clear preference for UFA-treated diets. On average, the rufous-collared sparrow consumed 0.46 g 2 h(-1) of UFA-rich diets and 0.12 g 2 h(-1) of SFA-rich diets. In turn, the consumption pattern of the common diuca-finch averaged 0.73 and 0.16 g 2 h(-1) for UFA-rich and SFA-rich diets, respectively. After a month of dietary acclimation to UFA-rich and SFA-rich diets, both species maintained body mass irrespective of the dietary regime. Additionally, the intestinal 4-NPA-CE activity exhibited by birds fed on a UFA-rich or SFA-rich diet was higher in the rufous-collared sparrow (39.0 ± 5.3 and 44.2 ± 7.3 µmol min(-1) g tissue(-1), respectively) than in the common diuca-finch (13.3 ± 1.9 and 11.2 ± 1.4 µmol min(-1) g tissue(-1), respectively). Finally, the intestinal a-NA-CE activity exhibited by the rufous-collared sparrow was about two times higher when consuming an UFA-rich diet. Our results suggest that the rufus-collared sparrow exhibits a greater capacity for intestinal FA hydrolysis, which would allow it to better deal with fats from different sources.

Membrane-bound intestinal enzymes of passerine birds: dietary and phylogenetic correlates.

Bird species exhibit great diversity in digestive tract morphology and enzymatic activity that is partly correlated with the chemical composition of their natural diets. However, no studies have assessed whether the activities of digestive enzymes of the enterocytes correlate with dietary chemical composition data analyzed as a continuous variable at an evolutionary scale. We used a phylogenetically explicit approach to examine the effect of diet on the hydrolytic activity of three digestive enzymes (maltase, sucrase, and aminopeptidase-N) in 16 species of songbirds (Order Passeriformes) from Central Chile. The total activities (µmol/min) of these enzymes were positively associated with body mass using both conventional least squares regressions and phylogenetically independent contrasts. After removing mass effects, we found a significant negative correlation between the ratio of aminopeptidase-N and maltase to the proportion of seeds found in the gizzard, but this relationship was no longer significant after controlling for phylogeny. When we analyzed the specific nutritional content of the diet, we found that the percentage of nitrogen in diet was negatively correlated with residual maltase activity and positively correlated with the ratio aminopeptidase-N/maltase. Given the large interspecific differences in biochemical capacity, we conclude that these differences reflect genetically determined evolutionary changes associated with the nutrient contents of each species' natural diet.