Bioenergetics and intestinal phenotypic flexibility in the microbiotherid marsupial (Dromiciops gliroides) from the temperate forest in South America

The microbiotherid marsupial Dromiciops gliroides inhabits the temperate forests of the Southern hemisphere, facing seasonal nutritional and energetic bottlenecks due to its apparently facultative insectivory/frugivory. In order to understand the physiological processes behind this ecological pattern, we studied the morpho-physiological changes that D. gliroides exhibits after dietary acclimation, in a sample of 21 wild-caught individuals fed over 1 month with ad libitum diet of: (1) fruit, (2) insects or (3) a mix of insects and fruit. In addition, we measured oxygen consumption (VO(2)) at resting conditions. We also performed enzyme assays (sucrase, maltase, trehalase and aminopeptidase N) and measurements of organ morphology. We found that D. gliroides cannot fulfil its nutrient requirements only from insects or fruit. It needs a mixed diet in order to maintain its body mass and energy balance. However, as a response of diet acclimation, individuals showed several-fold changes in the activities of aminopeptidase-N, maltase and sucrase (but not trehalase). This result, both the magnitude of change and the simultaneous effects on three enzymes suggests that D. gliroides could exhibit adaptive phenotypic plasticity in the activity of intestinal enzymes. This study suggests also that D. gliroides, the only living representative of the Microbiotheria order, exhibits physiological adaptations to a generalist diet.     

Multiple adaptive losses of alanine-glyoxylate aminotransferase mitochondrial targeting in fruit-eating bats

The enzyme alanine-glyoxylate aminotransferase 1 (AGT) functions to detoxify glyoxylate before it is converted into harmful oxalate. In mammals, mitochondrial targeting of AGT in carnivorous species versus peroxisomal targeting in herbivores is controlled by two signal peptides that correspond to these respective organelles. Differential expression of the mitochondrial targeting sequence (MTS) is considered an adaptation to diet-specific subcellular localization of glyoxylate precursors. Bats are an excellent group in which to study adaptive changes in dietary enzymes; they show unparalleled mammalian dietary diversification as well as independent origins of carnivory, frugivory, and nectarivory. We studied the AGT gene in bats and other mammals with diverse diets and found that the MTS has been lost in unrelated lineages of frugivorous bats. Conversely, species exhibiting piscivory, carnivory, insectivory, and sanguinivory possessed intact MTSs. Detected positive selection in the AGT of ancestral fruit bats further supports adaptations related to evolutionary changes in diet.     

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.     

Phenotypic flexibility in the intestinal enzymes of the African clawed frog Xenopus laevis

The intestinal plasticity of digestive enzymes of amphibian species is poorly known. The goal of this study was to characterize digestive enzyme profiles along the small intestine of adult frogs, Xenopus laevis, in response to an experimental diet. We acclimated adult X. laevis for 30 days either to carbohydrate-rich or protein-rich diets, and determined the morphology and digestive enzymes of the small intestine. We found a significant difference of aminopeptidase-N activity between carbohydrate-rich and protein-rich acclimated animals. We also found a little variation in the expression of maltase activity, which contrast with the proposed hypothesis about the existence of digestive tradeoff in vertebrates. This finding supports the adaptive modulation hypothesis and suggests that caution is called for when analyzing physiological data regarding assumed discrete trophic category of species.     

Origin of intestinal disaccharidases of Ascaris suum

Disaccharidases from the gut of Ascaris suum were investigated to determine whether they were synthesized by the worm or whether they were host enzymes adsorbed to the worms' intestinal cells. Alpha-d-glucoside glucohydrolase (maltase) (EC 3.2.1.20), Beta-d-fructofuranoside fructohydrolase (invertase) (EC 3.2.1.26) and 1-glucohydrolase (trehalase) (EC 3.2.1.28) from Ascaris were studied in both a membrane (brush border)-bound and solubilized form with regard to temperature stability and pH optima. Data collected were compared to similar data on hog intestinal enzymes. Worm maltase and trehalase were relatively heat labile, whereas the hog enzymes were more stable to heat inactivation. Worm invertase was heat stable in comparison to the hog enzyme. The pH optima for Ascaris maltase and invertase were different from those of hog disaccharidases, whereas the pH optimum for trehalase from both parasite and host were similar. Tissue homogenates of second-stage larvae contained measurable maltase, but not sucrase, or trehalase activity. Results suggested that Ascaris intestinal disaccharidases represent three distinct enzymes of parasite rather than host origin.     

Pancreatic and intestinal carbohydrases are matched to dietary starch level in wild passerine birds

Evolutionary shifts in diet composition are presumably accompanied by simultaneous changes in digestive physiology. The adaptive modulation hypothesis predicts that activities of digestive enzymes should match the relative levels of their substrates in an animal's diet so that available membrane space and synthetic energy are not wasted on enzymes in excess of need. However, previous studies on captive passerine birds showed high intraspecific phenotypic flexibility only in proteases but not in carbohydrases in response to varying diet composition. In this study, we measured the activities of pancreatic, intestinal, and hepatic enzymes in six wild-caught passerine species. We predicted that if the adaptive modulation hypothesis holds during evolutionary shifts in diet composition in birds, then mass-specific activities of digestive enzymes should be correlated positively with the content of their relevant substrates in species' diets. Whereas mass-specific activities of proteases (aminopeptidase-N, trypsin, chymotrypsin, alanine aminotransferase) were not correlated with estimated dietary protein content, mass-specific activities of all studied carbohydrases (amylase, maltase, sucrase) were positively correlated with estimated dietary starch content. We conclude that activities of carbohydrases but not proteases are evolutionarily matched to diet composition in passerine birds. We hypothesize that the need for nitrogen and essential amino acids can prevent the evolution of a low activity of proteases, even in species feeding on a low-protein diet.     

Carbohydrase activities in the bovine digestive tract

1. The carbohydrase activities of homogenates of mucosa from the abomasum, small intestine, caecum and colon, and of the pancreas of cattle were studied. 2. The disaccharidase activities were located mainly in the small intestine and showed a non-uniform pattern of distribution along the small intestine; trehalase activity was highest in the proximal part, lactase and cellobiase activities were highest in the proximal and middle parts and maltase activity was highest in the distal part. 3. The intestinal lactase and cellobiase activities were highest in the young calf and decreased with age, whereas the intestinal maltase and trehalase activities, which were very low compared with the lactase activity, did not change with age. 4. No intestinal sucrase or palatinase activity was detected in the calf or in the adult cow. 5. Homogenates of intestinal mucosa also exhibited amylase and dextranase activity. 6. Homogenates of the pancreas possessed a strong amylase activity and a weak maltase activity. The maltase activity did not change with age, whereas the amylase activity increased with age. 7. No marked differences were observed between the carbohydrase activities of calves fed solely on milk and those of calves given a concentrate-hay diet from 6 weeks of age.     

Dietary modulation of intestinal enzymes of the house sparrow (Passer domesticus): testing an adaptive hypothesis

Insectivorous/frugivorous passerine species studied so far lack the ability to modulate intestinal maltase activity, in contrast to galliformes. We tested for dietary modulation of small intestine (SI) enzymes including maltase in house sparrows to understand whether the difference between the galliformes on the one hand, and the passerines on the other, reflects a phylogenetic pattern (maltase modulated in galliformes but not passerines), a dietary pattern (maltase modulated in granivores but not insectivore/frugivores), some other pattern, or chance. We also tested the prediction that intestinal peptidase activity would be increased on a high protein (HP) diet. Birds were fed three diets high in starch, protein, or lipid for 10 days. For birds on the HP diet (60.3% protein) we observed the predicted upward modulation of aminopeptidase-N activity, as compared with the lower-protein, high starch (HS) (12.8% protein) diet. In contrast, birds eating the HS diet had similar maltase and sucrase activities, and only slightly higher isomaltase activity, compared with birds eating the high protein (HP), starch-free diet. Birds eating high lipid (HL) diet had low activities of both carbohydrases and peptidase. Considering that the statistical power of our tests was adequate, we conclude that house sparrows show little or no increase in carbohydrases in response to elevated dietary carbohydrate. We cannot reject the hypothesis that maltase lability among avian species has a phylogenetic component, or that high dietary fat has a depressing effect on both carbohydrase and peptidase activities.     

Quantifying carnivory by grizzly bears in a multi-ungulate system

Grizzly bears (Ursus arctos) cohabit landscapes with a diversity of ungulates, but the degree to which grizzly bears are carnivorous is unclear and likely varies across landscapes. We used stable isotopes of carbon and nitrogen to infer seasonal diets of grizzly bears in northern British Columbia while studying predator–prey dynamics in a largely undisturbed system. We found high seasonal variation in diets among individuals; males consumed more ungulate prey than did females throughout the year. In fall, both sexes increased their consumption of prey; large ungulates constituted 51% and 32% of the fall diets of males and females, respectively. This increase in carnivory appeared to be primarily associated with consumption of elk (Cervus elaphus). Estimates of prey proportions in the diets of grizzly bears were highly sensitive to the range of tissue to diet discrimination values that were incorporated in isotope models. Small changes in discrimination values resulted in estimated prey intakes that varied more than threefold as a percentage of the diet depending on sex and season. We caution against using standard discrimination values, and we recommend that diet reconstructions using stable isotopes be based on tissue-specific values that would be appropriate for the species of interest. © 2012 The Wildlife Society.     

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.Abbreviations m body mass - K _m Michaelis constant - K _m ^* apparent Michaelis constant - GI gastro-intestinal     

Storage and absorption in the digestive system of carnivorous and herbivorous prickleback fishes (Teleostei: Stichaeidae): ontogenetic, dietary, and phylogenetic effects

The effects of ontogeny, diet, and phylogeny on glycogen storage levels and esterase and alkaline phosphatase activities in four related prickleback fishes were determined in situ using quantitative histochemistry. Of these species, Cebidichthys violaceus and Xiphister mucosus shift from carnivory to herbivory at approximately 45 mm standard length (SL), whereas Xiphister atropurpureus and Anoplarchus purpurescens remain carnivores. Comparisons between small (30-40 mm SL) and larger (60-75 mm SL) wild-caught juveniles showed that glycogen storage levels and alkaline phosphatase activity were unchanged with ontogeny. Comparisons between the larger wild-caught juveniles and juveniles of the same size that had been raised on a high-protein animal diet revealed that glycogen storage level and alkaline phosphatase activity increased in all species in response to this diet. Esterase activity also increased in response to the high-protein animal diet in all four species but increased with ontogeny only in C. violaceus, X. mucosus, and X. atropurpureus, in the xiphisterine clade, and not in A. purpurescens, in the adjacent alectriine clade. Xiphister mucosus and X. atropurpureus showed indistinguishable responses in esterase activity to ontogeny and diet despite their divergent natural diets. Overall, glycogen storage level and alkaline phosphatase activity responded primarily to diet, whereas esterase activity was also influenced by ontogeny and phylogeny and differed between intestinal regions among the species.     

Ontogenetic changes in the diet of early post-settlement Scarus species (Pisces: Scaridae)

Ontogenetic changes in the diet of early post-settlement Scarus species are described, based on analyses of intestinal contents. There is a marked change-over from carnivory to herbivory. Newly settled individuals feed on Crustacea, primarily harpacticoid nauplii and adults, whilst larger juveniles almost exclusively ingest algae and sand. In comparison, the diets of recentlysettled Acanthuridae, Siganidae and Pomacanthidae were found to be almost exclusively herbivorous.     

The ecology of a continental evolutionary radiation: Is the radiation of sigmodontine rodents adaptive?

Evolutionary radiations on continents are less well‐understood and appreciated than those occurring on islands. The extent of ecological influence on species divergence can be evaluated to determine whether a radiation was ultimately the outcome of divergent natural selection or else arose mainly by nonecological divergence. Here, we used phylogenetic comparative methods to test distinct hypotheses corresponding to adaptive and nonadaptive evolutionary scenarios for the morphological evolution of sigmodontine rodents. Results showed that ecological variables (diet and life‐mode) explain little of the shape and size variation of sigmodontine skulls and mandibles. A Brownian model with varying rates for insectivory versus all other diets was the most likely evolutionary model. The insectivorous sigmodontines have a faster rate of morphological evolution than mice feeding on other diets, possibly due to stronger selection for features that aid insectivory. We also demonstrate that rapid early‐lineage diversification is not accompanied by high morphological divergence among subclades, contrasting with island results. The geographic size of continents permits spatial segregation to a greater extent than on islands, allowing for allopatric distributions and escape from interspecific competition. We suggest that continental radiations of rodents are likely to produce a pattern of high species diversification coupled with a low degree of phenotypic specialization.     

The fetal and postnatal development of small intestinal disaccharidases in the rabbit

The development of small intestinal enzymes (lactase, acid- and hetero beta-galactosidases, cellobiase, maltase, trehalase, and sucrase) was studied from 18 days after conception until birth in 24 rabbit fetuses, and during the postnatal period in 15 newborn, juvenile, and adult rabbits. Lactase, acid- and hetero beta-galactosidases, cellobiase, and trehalase activities increased significantly during the fetal stage, while changes in sucrase and maltase activities were not substantial. In the postnatal period, lactase and cellobiase activities decreased significantly whereas maltase, sucrase, and trehalase activities increased significantly to reach adult values by 30 days of age. The acid- and hetero beta-galactosidases remained unchanged.     

Maltase-glucoamylase and trehalase in the rabbit small intestine and kidney brush border membranes during postnatal development, the effects of hydrocortisone

Kidney and intestinal brush border membranes were isolated from 14-day-old rabbits and papa?n solubilized maltase-glucoamylase was purified to almost homogeneity from both membranes. Maltase-glucoamylase from kidney and intestine have the same molecular weight (669,000 daltons by AcA 22 gel filtration) and the same Km (4 mM, for maltose). Tris (Ki = 12.5 mM, for maltose) is a non-competitive inhibitor for both enzymes. In intestine, maltase and glucoamylase have low activity during the first two postnatal weeks and then undergo a sharp increase during the next 2 weeks. In contrast, for trehalase, adult levels are reached about 6 days after birth. Hydrocortisone injection to 10 days rabbits causes precocious increases in the specific activities of trehalase (3.6 x), maltase (5.2 x) and glucoamylase (7.4 x). Conversely, kidney maltase, glucoamylase and trehalase activities rise gradually from birth, reaching adult levels by the end of the third week. Administration of hydrocortisone to suckling rabbit does not affect either trehalase or maltase and glucoamylase in kidney brush border membrane.     

Test of the adaptive modulation hypothesis in rodents: dietary flexibility and enzyme plasticity.

The phenotypic response of digestive enzymes was assessed in two species of rodents with different foods habits. Species were Phyllotis darwini (omnivorous) and Octodon degus (herbivorous). The activity of sucrase, maltase and aminopeptidase-N were determined in vitro in animals feeding two contrasting diets. No effect of dietary chemistry on sucrase and maltase activities was observed. Nevertheless, aminopeptidase-N showed a reversible response to diet in P. darwini but not in O. degus. Through Principal Component Analysis we separated the specific and non-specific modulation of the enzymes. The analysis showed that aminopeptidase-N activity is up-regulated by dietary protein in P. darwini. Differences in the phenotypic response of this species apparently reflect the historic levels of specific substrates of the natural diets for this enzyme, linking dietary flexibility and digestive plasticity in an evolutionary context.     

Relationships between renal morphology and diet in 26 species of new world bats (suborder microchiroptera)

The renal morphology of 24 species of mormoopid and phyllostomid bats feeding on six different diets was examined to test evolutionary changes in several structural traits presumably led by dietary shifts from ancestral insectivorous diets. The kidneys of a fish-eating vespertilionid and an insect-eating emballonurid were also examined but not included in the phylogenetic comparison. The length, width, and breadth of the kidneys were used to calculate relative medullary thickness (RMT). Tissues were processed for stereological analysis, and the volumes of the kidney, nephron components, and vasculature were determined. RMT did not correlate with body mass in either animal-eating or plant-eating phyllostomid and mormoopid bats. The shift from insectivory to frugivory and nectarivory was accompanied by a reduction in RMT, a reduction in the percent of renal medulla, and an increase in the percent of renal cortex. No changes in these traits were observed in bats that shifted to carnivorous, omnivorous or sanguinivorous habits. No changes were observed in renal vasculature, in the percentage of cortical and medullary nephron components or of capillaries surrounding the nephrons in any feeding group. Vespertilionid and emballonurid species had similar values in all traits examined as compared to insectivorous phyllostomids and mormoopids. Our data suggest that diet does not influence a single area of the nephron, but rather the entire nephron such that the relative amounts of renal cortex and medulla are affected.     

Are levels of digestive enzyme activity related to the natural diet in passerine birds?

Digestive capabilities, such as the rates nutrient hydrolysis and absorption, may affect energy intake and ultimately feeding behavior. In birds, a high diversity in gut biochemical capabilities seems to support the existence of a correlation between the morphology and physiology of the intestinal tract and chemical features of the natural diet. However, studies correlating the activity of digestive enzymes and the feeding habits at an evolutionary scale are scarce. We investigated the effect of dietary habits on the digestive physiological characteristics of eight species of passerine birds from Central Chile. The Order Passeriformes is a speciose group with a broad dietary spectrum that includes omnivorous, granivorous and insectivorous species. We measured the activity of three enzymes: maltase, sucrase and aminopeptidase-N. Using an autocorrelation analysis to remove the phylogenetic effect, we found that dietary habits had no effect on enzymatic activity. However, we found that granivorous and omnivorous species had higher levels of disaccharidase activities and insectivores had the lowest. The major difference in enzymatic activity found at the inter-specific level, compared to the reported lower magnitude of enzyme modulation owing to dietary acclimation, suggests that these differences to some extent have a genetic basis. However, the lack of a clear association between diet categories and gut physiology suggested us that dietary categorizations do not always reflect the chemical composition of the ingested food.     

Diet and hormonal manipulation reveal cryptic genetic variation: implications for the evolution of novel feeding strategies

When experiencing resource competition or abrupt environmental change, animals often must transition rapidly from an ancestral diet to a novel, derived diet. Yet, little is known about the proximate mechanisms that mediate such rapid evolutionary transitions. Here, we investigated the role of diet-induced, cryptic genetic variation in facilitating the evolution of novel resource-use traits that are associated with a new feeding strategy—carnivory—in tadpoles of spadefoot toads (genus Spea). We specifically asked whether such variation in trophic morphology and fitness is present in Scaphiopus couchii, a species that serves as a proxy for ancestral Spea. We also asked whether corticosterone, a vertebrate hormone produced in response to environmental signals, mediates the expression of this variation. Specifically, we compared broad-sense heritabilities of tadpoles fed different diets or treated with exogenous corticosterone, and found that novel diets can expose cryptic genetic variation to selection, and that diet-induced hormones may play a role in revealing this variation. Our results therefore suggest that cryptic genetic variation may have enabled the evolutionary transition to carnivory in Spea tadpoles, and that such variation might generally facilitate rapid evolutionary transitions to novel diets.