Biomedical subjects

C Martínez del Rio

Publications and source records attributed to C Martínez del Rio.

10 recordsLinked to original sources

PubMed2003

Hummingbirds pay a high cost for a warm drink.

Endotherms must warm ingested food to body temperature. Food warming costs may be especially high for nectar-feeding birds, which can ingest prodigious volumes. We formulated a mathematical model to predict the cost of warming nectar as a function of nectar temperature and sugar concentration. This model predicts that the cost of warming nectar should: (1) decrease as a power function of nectar concentration, and (2) increase linearly with the difference between body temperature and nectar temperature. We tested our model on rufous hummingbirds (Selasphorus rufus). A typical experiment consisted of feeding birds nectar of a given concentration at 39 degrees C (equivalent to body temperature) and then at 4 degrees C, and vice versa. We used the percentage change in metabolic rate between the two food temperatures to estimate the cost of warming nectar. The model's predictions were accurately met. When birds had to hover rather than perch during feeding bouts, estimated food-warming costs were only slightly lower. The cost of warming nectar to body temperature appears to be an important yet overlooked aspect of the energy budgets of nectar-feeding birds. Hummingbirds feeding on 5% sucrose solutions at 4 degrees C have to increase their metabolic rate by an amount equivalent to that elicited by a 15 degrees C drop in ambient temperature.

Administration, Oral↗

PubMed2003

How important are columnar cacti as sources of water and nutrients for desert consumers? A review.

Succulent CAM plants, such as columnar cacti, are important physiognomic elements of many arid lands. Although, these plans are often ecologically important because they provide abundant resources in the form of nectar and fruit, their contribution to the energy, nutrient and water budgets of consumes has not been quantified. We describe an isotopic approach that allows quantifying the ecological importance of CAM succulents. We first briefly review our work on the interaction between saguaros, an archetypical CAM succulent, and the desert doves that feed on its fruit. We then describe the potential importance of saguaro fruit as a function of its abundance, macronutrient composition, and seasonal availability. We argue that the resources provided by saguaros do much to satisfy the energy and water requirements of the birds that reside in hot subtropical deserts during the summer. We then describe the carbon isotope composition of saguaros and of the plant community in which they are imbedded and use two species of desert doves to illustrate how stable isotopes can reveal the importance of a single plant as a source of carbon and water for consumers. The second section of this review presents new data on the importance of saguaros for the entire community of birds that inhabit the Sonoran Desert during the summer. We show how the resources of saguaro reach across dietary guilds and account for a large proportion of the diet of many insectivorous species as well as that of granivorous and frugivorous species. We demonstrate that many of these species probably obtain significant water as well as nutrients from saguaro fruit. Finally, we point out the current limitations of using deuterium as a water tracer in animal systems.

Animals↗

PubMed2001

Diet and the evolution of digestion and renal function in phyllostomid bats.

Bat species in the monophyletic family Phyllostomidae feed on blood, insects, small vertebrates, nectar, fruit and complex omnivorous mixtures. We used nitrogen stable isotope ratios to characterize bat diets and adopted a phylogenetically informed approach to investigate the physiological changes that accompany evolutionary diet changes in phyllostomids. We found that nitrogen stable isotopes separated plant-eating from animal-eating species. The blood of the latter was enriched in (15)N. A recent phylogenetic hypothesis suggests that with the possible exception of carnivory, which may have evolved twice, all diets evolved only once from insectivory. The shift from insectivory to nectarivory and frugivory was accompanied by increased intestinal sucrase and maltase activity, decreased trehalase activity, and reduced relative medullary thickness of kidneys. The shift from insectivory to sanguinivory and carnivory resulted in reduced trehalase activity. Vampire bats are the only known vertebrates that do not exhibit intestinal maltase activity. We argue that these physiological changes are adaptive responses to evolutionary diet shifts.

Journal Article↗

PubMed1998

Natural abundance variations in stable isotopes and their potential uses in animal physiological ecology.

Chemical, biological, and physical processes lead to distinctive "isotopic signatures" in biological materials that allow tracing of the origins of organic substances. Isotopic variation has been extensively used by plant physiological ecologists and by paleontologists, and recently ecologists have adopted the use of stable isotopes to measure ecosystem patterns and processes. To date, animal physiological ecologists have made minimal use of naturally occurring stable isotopes as tracers. Here we provide a review of the current and potential uses of naturally occurring stable isotopes in animal physiological ecology. We outline the physical and biological processes that lead to variation in isotopic abundance in plants and animals. We summarize current uses in animal physiological ecology (diet reconstruction and animal movement patterns), and suggest areas of research where the use of stable isotopes can be fruitful (protein balance and turnover and the allocation of dietary nutrients). We argue that animal physiological ecologists can benefit from including the measurement of naturally occurring stable isotopes in their battery of techniques. We also argue that animal physiologists can make an important contribution to the emerging field of stable isotopes in biology by testing experimentally the plethora of assumptions upon which the techniques rely.

Animal Nutritional Physiological Phenomena↗

PubMed1993

Ontogenesis of intestine morphology and intestinal disaccharidases in chickens (Gallus gallus) fed contrasting purified diets.

Two groups of growing posthatching Cornish x Rock cross chickens were fed with either a carbohydrate-containing (52.5%) or a carbohydrate-free diet. At 36 days after hatching some of the chicks in each group were shifted to the opposite diet. Chickens fed on a carbohydrate-containing diet grew faster and achieved higher asymptotic masses than chickens fed on a carbohydrate-free diet. Chickens fed on a carbohydrate-free diet had longer intestines and larger intestinal areas than chickens of the same mass fed on a carbohydrate-containing diet. In both groups sucrase and maltase activity (standardized by either intestinal area or mass) increased from day 1 to approximately day 17. After day 17, chickens fed on a carbohydrate-containing diet exhibited 1.8 and 1.9 times higher sucrase and maltase activities per unit intestinal area, respectively, than chickens fed on a carbohydrate-free diet. Analysis of covariance was used to estimate the contribution of sucrase and the sucrase-independent maltases to maltase activity, and to estimate the effect of diet on the sucrase-independent maltases. Sucrase contributed 80% and 75% of the maltase activity in carbohydrate and carbohydrate-free fed chickens, respectively. Chickens shifted from a carbohydrate-free to a carbohydrate diet converged in gross intestinal morphology and intestinal sucrase and maltase levels with carbohydrate-fed chickens within 8 days. Chickens shifted from carbohydrate to carbohydrate-free diets, in contrast, did not show appreciable changes in intestinal length and after 8 days had not reduced levels of sucrase and maltase to those of chickens fed on the carbohydrate-free diet. A comparison of integrated maltase intestinal activity with published data on glucose uptake showed that the ratio of maltose hydrolysis to glucose uptake seemed to be about 7 and to remain relatively invariant during ontogeny. Because so little is known about the interaction between hydrolysis and uptake in vivo, it is difficult to determine if this relatively high ratio represents excess hydrolytic capacity or if it is needed to provide high lumenal glucose concentrations that maximize uptake.

Animals↗

PubMed1988

Intestinal brush border membrane-bound disaccharidases of the American alligator, Alligator mississippiensis.

1. The disaccharidase activities of the small intestines of American alligators (Alligator mississippiensis) were studied in epithelial scrapes and brush-border membrane preparations. 2. Maltase, isomaltase and trehalase activities were found. Activities of these enzymes were higher in the proximal small intestine and decreased distally. 3. Disaccharidase activities were enriched 12-15 times in brush-border membrane preparations, compared with mucosa/enterocyte crude homogenates and were co-enriched with the brush-border membrane marker alkaline phosphatase. 3. The pH optima were: maltase 6.5; isomaltase 5.6; and trehalase 5.8. The Q10 of maltase, the most active enzyme, was equal to 1.82. 4. In reptiles, as in mammals, disaccharidase activities may be correlated with feeding habits. The co-occurrence of sucrase and isomaltase may not be a common feature of vertebrates.

Alligators and Crocodiles↗

PubMedDate not supplied

Test, rejection, and reformulation of a chemical reactor-based model of gut function in a fruit-eating bird.

We explored modulation of retention time in cedar waxwings (Bombycilla cedrorum) by feeding them diets varying in hexose concentration. Our goals were to (1) test three predictions of a chemical reactor-based model of how guts might respond optimally to diet shifts; (2) determine whether modulation of retention time can occur quickly, thereby facilitating rapid changes in diet; (3) tease apart the relative influence of ingestion rate and nutrient concentration on retention time; and (4) examine the degree of axial mixing in the intestine and its relationship with retention time. The model's predictions were rejected: mean retention time did not decrease, ingestion rate did not increase, and glucose assimilation efficiency did not decrease with increased hexose concentration of the diet. Instead, birds displayed maximal intake rate at intermediate sugar concentration, and mouth to cloaca mean retention times increased with hexose concentration. Significant modulation of retention time occurred quickly, within 3 h of exposure to a different diet. Birds did equally well in terms of total energy assimilated on diets differing 3.3-fold in hexose concentration (from 500 mmol/L to 1660 mmol/L) but showed reduced intake when fed food with low hexose concentration (110 mmol/L). Far more variation in retention time was explained by direct effects of ingestion rate than by direct effects of hexose concentration. Finally, a gut dispersion index that measured degree of axial mixing was positively correlated with mean retention time, indicating that higher retention times are accompanied by increased axial mixing. We propose a modification of the assumptions of the original model. The resulting "osmotic constraint" model better captures the interaction between feeding rate and digestive function in fruit-eating birds.

Animals↗

PubMedDate not supplied

Does gut function limit hummingbird food intake?

Many nectar-feeding bird species decrease food intake when sugar concentration in food is increased. This feeding response can be explained by two alternative hypotheses: compensatory feeding and physiological constraint. The compensatory feeding hypothesis predicts that if birds vary intake to maintain a constant energy intake to match energy expenditures, then they should increase intake when expenditures are increased. Broad-tailed hummingbirds were presented with sucrose solutions at four concentrations (292, 584, 876, and 1,168 mmol L(-1)) and exposed to two environmental temperatures (10 degrees and 22 degrees C). Birds decreased volumetric food intake in response to sugar concentration. However, when they were exposed to a relatively sudden drop in environmental temperature and, hence, to an acute increase in thermoregulatory energy expenditures, they did not increase their rate of energy consumption and lost mass. These results support the existence of a physiological constraint on feeding intake. A simple chemical reactor model based on intestinal morphology and in vitro measurements of sucrose hydrolysis predicted observed intake rates closely. This model suggests that intestinal sucrose hydrolysis rates were near maximal and, thus, may have imposed limits to sugar assimilation. Although sugar assimilation was high (95%), the proportions of excreted sucrose, glucose, and fructose found in excreta differed significantly. The monosaccharides glucose and fructose were about eight and three times more abundant than sucrose, respectively. Broad-tailed hummingbirds are small high-altitude endotherms that face unpredictable weather and the energetic expense of premigratory fattening. Digestive processes have the potential to impose severe challenges to their energy budgets.

Adaptation, Physiological↗

PubMedDate not supplied

The membrane-bound intestinal enzymes of waxwings and thrushes: adaptive and functional implications of patterns of enzyme activity.

Cedar waxwings (Bombycilla cedrorum) feed predominantly on fruits that are rich in simple sugars and low in nitrogen, supplementing this diet with arthropod prey during the summer months as well as flowers and tree sap in springtime. In contrast, thrushes feed extensively on fatty, protein-rich invertebrate prey, supplemented with sugary and lipid-rich fruits. Simple sugars and fats are digested and/or absorbed by distinctly different physiological mechanisms, which suggests the possibility of contrasting digestive strategies in animals specialized to diets containing one of these two energy sources. In this study, we quantified enzymatic activity of three membrane-bound intestinal enzymes of cedar waxwings and five species of thrushes to explore this aspect of their digestive physiology. These enzymes catalyze the final steps in the digestion of carbohydrates (sucrase-isomaltase and maltase-glucoamylase) and protein (aminopeptidase-N). The two carbohydrases are homologous enzymes with overlapping functions; both enzymes catalyze the hydrolysis of maltase and isomaltase. The membrane-bound digestive enzyme systems that we described for cedar waxwings and thrushes can be explained by the particular nutrients contained within their respective natural diets. Consistent with previous work, cedar waxwings displayed intestinal sucrase activity, whereas thrushes did not. Correspondingly, cedar waxwings eat some foods containing sucrose, whereas thrushes do not. Sucrase-isomaltase conferred all maltase and isomaltase activity in cedar waxwings. In contrast, all maltase and isomaltase activity in thrushes was necessarily sucrase independent, which indicated the presence of maltase-glucoamylase. The absence of sucrase-independent maltase activity in cedar waxwings suggests that sucrase-isomaltase obviates the need for maltase-glucoamylase. Indeed, total maltase and isomaltase activities were much higher in cedar waxwings than in thrushes. Neither waxwings nor thrushes eat starchy foods; sucrase-isomaltase in waxwings and maltaseglucoamylase in thrushes probably function in digesting glycogen in animal foods. We suggest that digestive traits associated with specialization to monosaccharide-rich fruits (lack of a grinding gizzard) by frugivorous waxwings and thrushes may prevent utilization of starchy seeds. Total aminopeptidase-N activity in cedar waxwings was indistinguishable from the allometric pattern among thrush species, but the distribution of this enzyme along the intestines of waxwings and thrushes was distinctly different, which demonstrates that total enzyme activity can be insufficient as a descriptor of the functional activity of brush border enzymes. Aminopeptidase-N activity peaked in the anterior part of the intestines of thrushes and in the terminal portion of the intestines of waxwings, which suggests contrasting strategies for protein digestion from fatty versus sugary diets, respectively.

Animals↗

PubMedDate not supplied

Dietary flexibility and intestinal plasticity in birds: a field and laboratory study.

The adaptive modulation hypothesis posits that the expression of digestive proteins should be modulated in response to intake of their respective substrates. A corollary of this hypothesis suggests that dietary flexibility and digestive plasticity should be correlated. We examined these two hypotheses in two granivorous Chilean birds (Zonotrichia capensis and Diuca diuca) that differ in dietary breadth. D. diuca is a strict granivore, whereas Z. capensis also eats insects. In field-caught birds, the activity of the intestinal dipeptidase aminopeptidase-N was positively correlated with intake of insects in Z. capensis but not in D. diuca. This is the first field documentation of modulation of intestinal enzymes by diet in birds. Intestinal maltase and sucrase activities were not correlated with seed (vs. insect) intake in either species. In the laboratory, captive birds of both species exhibited similar modulation of membrane-bound intestinal hydrolases when fed on synthetic diets of contrasting carbohydrate and protein composition. Maltase, sucrase, and aminopeptidase-N activities were significantly higher in birds fed on the carbohydrate-free than those on the carbohydrate-containing diet. Activities of the three enzymes were positively correlated. Therefore, this increase probably resulted from nonspecific increases of all enzymes resulting from intake of the carbohydrate-free diet. Principal components analysis separating the effect of diet on specific and on nonspecific modulation revealed that diet had a strong effect on nonspecific activity of intestinal enzymes in both Z. capensis and D. diuca. Diet also significantly affected aminopeptidase-N activities when the effect of diet on nonspecific modulation was removed. Birds fed on the carbohydrate-free, high-protein diet had significantly higher specific aminopeptidase-N activities than those fed on the carbohydrate-containing diet. Our results cast doubts on the notion that dietary flexibility and the plasticity of the gut's enzymes are necessarily correlated and on the general validity of the adaptive modulation hypothesis.

Adaptation, Biological↗